* combine.c (subst): Use CLASS_CANNOT_CHANGE_MODE and

        CLASS_CANNOT_CHANGE_MODE_P instead of CLASS_CANNOT_CHANGE_SIZE
        and hard-coded tests.
        (simplify_set): Likewise.
        (gen_lowpart_for_combine): Likewise.
        * emit-rtl.c (gen_lowpart_common): Likewise.
        * global.c (find_reg): Likewise.
        * local-alloc.c (find_free_reg): Likewise.
        * recog.c (register_operand): Likewise.
        * regclass.c (init_reg_sets_1): Likewise.
        (record_operand_costs, regclass): Likewise.
        * reload.c (push_reload): Likewise.
        * reload1.c (choose_reload_regs): Likewise.
        * flow.c (mark_used_regs): Conditionally set REG_CHANGES_MODE.
        * local-alloc.c (struct qty): Rename changes_size to changes_mode.
        Update all references.
        * regs.h (struct reg_info_def): Likewise.
        (REG_CHANGES_MODE): Rename from REG_CHANGES_SIZE.
        * tm.texi (CLASS_CANNOT_CHANGE_MODE): Document.
        (CLASS_CANNOT_CHANGE_MODE_P): Likewise.

        * config/alpha/alpha.h (CLASS_CANNOT_CHANGE_MODE): Rename.
        (CLASS_CANNOT_CHANGE_MODE_P): New.
        * config/mips/mips.h: Likewise.
        * config/pa/pa32-regs.h: Likewise.
        * config/pa/pa64-regs.h: Likewise.
        * config/rs6000/rs6000.h: Likewise.
        * config/sh/sh.h: Likewise.
        * config/ia64/ia64.h (CLASS_CANNOT_CHANGE_MODE): New.
        (CLASS_CANNOT_CHANGE_MODE_P): New.
        * config/avr/avr.h (CLASS_CANNOT_CHANGE_SIZE): Remove dead code.
        * config/d30v/d30v.h: Likewise.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@34526 138bc75d-0d04-0410-961f-82ee72b054a4

21 files changed, 201 insertions, 131 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 6d1decfffa8..d91bbe864a2 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,38 @@
+2000-06-13  Richard Henderson  <rth@cygnus.com>
+
+	* combine.c (subst): Use CLASS_CANNOT_CHANGE_MODE and
+	CLASS_CANNOT_CHANGE_MODE_P instead of CLASS_CANNOT_CHANGE_SIZE
+	and hard-coded tests.
+	(simplify_set): Likewise.
+	(gen_lowpart_for_combine): Likewise.
+	* emit-rtl.c (gen_lowpart_common): Likewise.
+	* global.c (find_reg): Likewise.
+	* local-alloc.c (find_free_reg): Likewise.
+	* recog.c (register_operand): Likewise.
+	* regclass.c (init_reg_sets_1): Likewise.
+	(record_operand_costs, regclass): Likewise.
+	* reload.c (push_reload): Likewise.
+	* reload1.c (choose_reload_regs): Likewise.
+	* flow.c (mark_used_regs): Conditionally set REG_CHANGES_MODE.
+	* local-alloc.c (struct qty): Rename changes_size to changes_mode.
+	Update all references.
+	* regs.h (struct reg_info_def): Likewise.
+	(REG_CHANGES_MODE): Rename from REG_CHANGES_SIZE.
+	* tm.texi (CLASS_CANNOT_CHANGE_MODE): Document.
+	(CLASS_CANNOT_CHANGE_MODE_P): Likewise.
+
+	* config/alpha/alpha.h (CLASS_CANNOT_CHANGE_MODE): Rename.
+	(CLASS_CANNOT_CHANGE_MODE_P): New.
+	* config/mips/mips.h: Likewise.
+	* config/pa/pa32-regs.h: Likewise.
+	* config/pa/pa64-regs.h: Likewise.
+	* config/rs6000/rs6000.h: Likewise.
+	* config/sh/sh.h: Likewise.
+	* config/ia64/ia64.h (CLASS_CANNOT_CHANGE_MODE): New.
+	(CLASS_CANNOT_CHANGE_MODE_P): New.
+	* config/avr/avr.h (CLASS_CANNOT_CHANGE_SIZE): Remove dead code.
+	* config/d30v/d30v.h: Likewise.
+
 2000-06-13  J. David Anglin  <dave@hiauly1.hia.nrc.ca>
 
 	* configure.in: Add AC_TYPE_GETGROUPS test.
diff --git a/gcc/combine.c b/gcc/combine.c
index 8d7cadccbb7..6010cb7905c 100644
--- a/gcc/combine.c
+++ b/gcc/combine.c
@@ -3400,15 +3400,15 @@ subst (x, from, to, in_dest, unique_copy)
 		      )
 		    return gen_rtx_CLOBBER (VOIDmode, const0_rtx);
 
-#ifdef CLASS_CANNOT_CHANGE_SIZE
+#ifdef CLASS_CANNOT_CHANGE_MODE
 		  if (code == SUBREG
 		      && GET_CODE (to) == REG
 		      && REGNO (to) < FIRST_PSEUDO_REGISTER
 		      && (TEST_HARD_REG_BIT
-			  (reg_class_contents[(int) CLASS_CANNOT_CHANGE_SIZE],
+			  (reg_class_contents[(int) CLASS_CANNOT_CHANGE_MODE],
 			   REGNO (to)))
-		      && (GET_MODE_BITSIZE (GET_MODE (to)) 
-			  != GET_MODE_BITSIZE (GET_MODE (x))))
+		      && CLASS_CANNOT_CHANGE_MODE_P (GET_MODE (to),
+						     GET_MODE (x)))
 		    return gen_rtx_CLOBBER (VOIDmode, const0_rtx);
 #endif
 
@@ -5036,13 +5036,13 @@ simplify_set (x)
       && (GET_MODE_SIZE (GET_MODE (src))
 	  < GET_MODE_SIZE (GET_MODE (SUBREG_REG (src))))
 #endif
-#ifdef CLASS_CANNOT_CHANGE_SIZE
+#ifdef CLASS_CANNOT_CHANGE_MODE
       && ! (GET_CODE (dest) == REG && REGNO (dest) < FIRST_PSEUDO_REGISTER
 	    && (TEST_HARD_REG_BIT
-		(reg_class_contents[(int) CLASS_CANNOT_CHANGE_SIZE],
+		(reg_class_contents[(int) CLASS_CANNOT_CHANGE_MODE],
 		 REGNO (dest)))
-	    && (GET_MODE_SIZE (GET_MODE (src))
-		!= GET_MODE_SIZE (GET_MODE (SUBREG_REG (src)))))
+	    && CLASS_CANNOT_CHANGE_MODE_P (GET_MODE (src),
+					   GET_MODE (SUBREG_REG (src))))
 #endif				  
       && (GET_CODE (dest) == REG
 	  || (GET_CODE (dest) == SUBREG
@@ -9680,13 +9680,15 @@ gen_lowpart_for_combine (mode, x)
     }
 
   result = gen_lowpart_common (mode, x);
+#ifdef CLASS_CANNOT_CHANGE_MODE
   if (result != 0
       && GET_CODE (result) == SUBREG
       && GET_CODE (SUBREG_REG (result)) == REG
       && REGNO (SUBREG_REG (result)) >= FIRST_PSEUDO_REGISTER
-      && (GET_MODE_SIZE (GET_MODE (result))
-	  != GET_MODE_SIZE (GET_MODE (SUBREG_REG (result)))))
-    REG_CHANGES_SIZE (REGNO (SUBREG_REG (result))) = 1;
+      && CLASS_CANNOT_CHANGE_MODE_P (GET_MODE (result),
+				     GET_MODE (SUBREG_REG (result))))
+    REG_CHANGES_MODE (REGNO (SUBREG_REG (result))) = 1;
+#endif
 
   if (result)
     return result;
diff --git a/gcc/config/alpha/alpha.h b/gcc/config/alpha/alpha.h
index 45ebbd83f3f..0721392fcea 100644
--- a/gcc/config/alpha/alpha.h
+++ b/gcc/config/alpha/alpha.h
@@ -860,9 +860,14 @@ enum reg_class { NO_REGS, GENERAL_REGS, FLOAT_REGS, ALL_REGS,
  ((GET_MODE_SIZE (MODE) + UNITS_PER_WORD - 1) / UNITS_PER_WORD)
 
 /* If defined, gives a class of registers that cannot be used as the
-   operand of a SUBREG that changes the size of the object.  */
+   operand of a SUBREG that changes the mode of the object illegally.  */
 
-#define CLASS_CANNOT_CHANGE_SIZE	FLOAT_REGS
+#define CLASS_CANNOT_CHANGE_MODE	FLOAT_REGS
+
+/* Defines illegal mode changes for CLASS_CANNOT_CHANGE_MODE.  */
+
+#define CLASS_CANNOT_CHANGE_MODE_P(FROM,TO) \
+  (GET_MODE_SIZE (FROM) != GET_MODE_SIZE (TO))
 
 /* Define the cost of moving between registers of various classes.  Moving
    between FLOAT_REGS and anything else except float regs is expensive. 
diff --git a/gcc/config/avr/avr.h b/gcc/config/avr/avr.h
index f459bc038da..b357af5372b 100644
--- a/gcc/config/avr/avr.h
+++ b/gcc/config/avr/avr.h
@@ -848,22 +848,6 @@ enum reg_class {
    This macro helps control the handling of multiple-word values in
    the reload pass.  */
 
-#undef CLASS_CANNOT_CHANGE_SIZE
-/* `CLASS_CANNOT_CHANGE_SIZE'
-   If defined, a C expression for a class that contains registers
-   which the compiler must always access in a mode that is the same
-   size as the mode in which it loaded the register.
-
-   For the example, loading 32-bit integer or floating-point objects
-   into floating-point registers on the Alpha extends them to 64-bits.
-   Therefore loading a 64-bit object and then storing it as a 32-bit
-   object does not store the low-order 32-bits, as would be the case
-   for a normal register.  Therefore, `alpha.h' defines this macro as
-   `FLOAT_REGS'.
-
-   Three other special macros describe which operands fit which
-   constraint letters.  */
-
 #define CONST_OK_FOR_LETTER_P(VALUE, C)				\
   ((C) == 'I' ? (VALUE) >= 0 && (VALUE) <= 63 :			\
    (C) == 'J' ? (VALUE) <= 0 && (VALUE) >= -63:			\
diff --git a/gcc/config/d30v/d30v.h b/gcc/config/d30v/d30v.h
index c97ff98032b..d4556293499 100644
--- a/gcc/config/d30v/d30v.h
+++ b/gcc/config/d30v/d30v.h
@@ -1759,17 +1759,6 @@ extern enum reg_class reg_class_from_letter[];
  ? ((GET_MODE_SIZE (MODE) + 8 - 1) / 8)					\
  : ((GET_MODE_SIZE (MODE) + 4 - 1) / 4))
 
-/* If defined, a C expression for a class that contains registers which the
-   compiler must always access in a mode that is the same size as the mode in
-   which it loaded the register.
-
-   For the example, loading 32-bit integer or floating-point objects into
-   floating-point registers on the Alpha extends them to 64-bits.  Therefore
-   loading a 64-bit object and then storing it as a 32-bit object does not
-   store the low-order 32-bits, as would be the case for a normal register.
-   Therefore, `alpha.h' defines this macro as `FLOAT_REGS'.  */
-/* #define CLASS_CANNOT_CHANGE_SIZE */
-
 /* A C expression that defines the machine-dependent operand constraint letters
    (`I', `J', `K', .. 'P') that specify particular ranges of integer values.
    If C is one of those letters, the expression should check that VALUE, an
diff --git a/gcc/config/ia64/ia64.h b/gcc/config/ia64/ia64.h
index cc5ba5b214d..522c9c7ba80 100644
--- a/gcc/config/ia64/ia64.h
+++ b/gcc/config/ia64/ia64.h
@@ -1046,6 +1046,15 @@ enum reg_class
        || (CLASS) == FR_INT_REGS) && (MODE) == XFmode) ? 1		\
    : (GET_MODE_SIZE (MODE) + UNITS_PER_WORD - 1) / UNITS_PER_WORD)
 
+/* If defined, gives a class of registers that cannot be used as the
+   operand of a SUBREG that changes the mode of the object illegally.  */
+
+#define CLASS_CANNOT_CHANGE_MODE        FR_REGS
+
+/* Defines illegal mode changes for CLASS_CANNOT_CHANGE_MODE.  */
+
+#define CLASS_CANNOT_CHANGE_MODE_P(FROM,TO) 1
+
 /* A C expression that defines the machine-dependent operand constraint letters
    (`I', `J', `K', .. 'P') that specify particular ranges of integer values.  */
 
diff --git a/gcc/config/mips/mips.h b/gcc/config/mips/mips.h
index 1ff81cbb2cd..e723dfc2a70 100644
--- a/gcc/config/mips/mips.h
+++ b/gcc/config/mips/mips.h
@@ -2043,10 +2043,15 @@ extern enum reg_class mips_char_to_class[];
    : CLASS_UNITS (MODE, UNITS_PER_WORD))
 
 /* If defined, gives a class of registers that cannot be used as the
-   operand of a SUBREG that changes the size of the object.  */
+   operand of a SUBREG that changes the mode of the object illegally.  */
 
-#define CLASS_CANNOT_CHANGE_SIZE					\
+#define CLASS_CANNOT_CHANGE_MODE \
   (TARGET_FLOAT64 && ! TARGET_64BIT ? FP_REGS : NO_REGS)
+
+/* Defines illegal mode changes for CLASS_CANNOT_CHANGE_MODE.  */
+
+#define CLASS_CANNOT_CHANGE_MODE_P(FROM,TO) \
+  (GET_MODE_SIZE (FROM) != GET_MODE_SIZE (TO))
 
 /* Stack layout; function entry, exit and calling.  */
 
diff --git a/gcc/config/pa/pa32-regs.h b/gcc/config/pa/pa32-regs.h
index d201f0e009a..21442dbc234 100644
--- a/gcc/config/pa/pa32-regs.h
+++ b/gcc/config/pa/pa32-regs.h
@@ -243,7 +243,11 @@ enum reg_class { NO_REGS, R1_REGS, GENERAL_REGS, FPUPPER_REGS, FP_REGS,
 
 /* This may not actually be necessary anymore.  But until I can prove
    otherwise it will stay.  */
-#define CLASS_CANNOT_CHANGE_SIZE NO_REGS
+#define CLASS_CANNOT_CHANGE_MODE	NO_REGS
+
+/* Defines illegal mode changes for CLASS_CANNOT_CHANGE_MODE.  */
+#define CLASS_CANNOT_CHANGE_MODE_P(FROM,TO) \
+  (GET_MODE_SIZE (FROM) != GET_MODE_SIZE (TO))
 
 /* The same information, inverted:
    Return the class number of the smallest class containing
diff --git a/gcc/config/pa/pa64-regs.h b/gcc/config/pa/pa64-regs.h
index 9d53adce920..a061d2f045c 100644
--- a/gcc/config/pa/pa64-regs.h
+++ b/gcc/config/pa/pa64-regs.h
@@ -229,9 +229,15 @@ enum reg_class { NO_REGS, R1_REGS, GENERAL_REGS, FPUPPER_REGS, FP_REGS,
   {0x00000000, 0x10000000},	/* SHIFT_REGS */		\
   {0xfffffffe, 0x1fffffff}}	/* ALL_REGS */
 
-/* This may not actually be necessary anymore.  But until I can prove
+/* If defined, gives a class of registers that cannot be used as the
+   operand of a SUBREG that changes the mode of the object illegally.  */
+/* ??? This may not actually be necessary anymore.  But until I can prove
    otherwise it will stay.  */
-#define CLASS_CANNOT_CHANGE_SIZE (FP_REGS)
+#define CLASS_CANNOT_CHANGE_MODE	(FP_REGS)
+
+/* Defines illegal mode changes for CLASS_CANNOT_CHANGE_MODE.  */
+#define CLASS_CANNOT_CHANGE_MODE_P(FROM,TO) \
+  (GET_MODE_SIZE (FROM) != GET_MODE_SIZE (TO))
 
 /* The same information, inverted:
    Return the class number of the smallest class containing
diff --git a/gcc/config/rs6000/rs6000.h b/gcc/config/rs6000/rs6000.h
index 94f6c10fa68..fdbcb977dc9 100644
--- a/gcc/config/rs6000/rs6000.h
+++ b/gcc/config/rs6000/rs6000.h
@@ -1134,9 +1134,14 @@ enum reg_class
   : ((GET_MODE_SIZE (MODE) + UNITS_PER_WORD - 1) / UNITS_PER_WORD))
 
 /* If defined, gives a class of registers that cannot be used as the
-   operand of a SUBREG that changes the size of the object.  */
+   operand of a SUBREG that changes the mode of the object illegally.  */
 
-#define CLASS_CANNOT_CHANGE_SIZE      FLOAT_REGS
+#define CLASS_CANNOT_CHANGE_MODE        FLOAT_REGS
+
+/* Defines illegal mode changes for CLASS_CANNOT_CHANGE_MODE.  */
+
+#define CLASS_CANNOT_CHANGE_MODE_P(FROM,TO) \
+  (GET_MODE_SIZE (FROM) != GET_MODE_SIZE (TO))
 
 /* Stack layout; function entry, exit and calling.  */
 
diff --git a/gcc/config/sh/sh.h b/gcc/config/sh/sh.h
index 6f14d3c5bed..981a802baa7 100644
--- a/gcc/config/sh/sh.h
+++ b/gcc/config/sh/sh.h
@@ -825,9 +825,14 @@ extern enum reg_class reg_class_from_letter[];
      ((GET_MODE_SIZE (MODE) + UNITS_PER_WORD - 1) / UNITS_PER_WORD)
 
 /* If defined, gives a class of registers that cannot be used as the
-   operand of a SUBREG that changes the size of the object.  */
+   operand of a SUBREG that changes the mode of the object illegally.  */
 
-#define CLASS_CANNOT_CHANGE_SIZE	DF_REGS
+#define CLASS_CANNOT_CHANGE_MODE        DF_REGS
+
+/* Defines illegal mode changes for CLASS_CANNOT_CHANGE_MODE.  */
+
+#define CLASS_CANNOT_CHANGE_MODE_P(FROM,TO) \
+  (GET_MODE_SIZE (FROM) != GET_MODE_SIZE (TO))
 
 /* Stack layout; function entry, exit and calling.  */
 
diff --git a/gcc/emit-rtl.c b/gcc/emit-rtl.c
index fcabed2e528..18a016ae041 100644
--- a/gcc/emit-rtl.c
+++ b/gcc/emit-rtl.c
@@ -737,12 +737,12 @@ gen_lowpart_common (mode, x)
 	       /* integrate.c can't handle parts of a return value register. */
 	       && (! REG_FUNCTION_VALUE_P (x)
 		   || ! rtx_equal_function_value_matters)
-#ifdef CLASS_CANNOT_CHANGE_SIZE
-	       && ! (GET_MODE_SIZE (mode) != GET_MODE_SIZE (GET_MODE (x))
+#ifdef CLASS_CANNOT_CHANGE_MODE
+	       && ! (CLASS_CANNOT_CHANGE_MODE_P (mode, GET_MODE (x))
 		     && GET_MODE_CLASS (GET_MODE (x)) != MODE_COMPLEX_INT
 		     && GET_MODE_CLASS (GET_MODE (x)) != MODE_COMPLEX_FLOAT
 		     && (TEST_HARD_REG_BIT
-			 (reg_class_contents[(int) CLASS_CANNOT_CHANGE_SIZE],
+			 (reg_class_contents[(int) CLASS_CANNOT_CHANGE_MODE],
 			  REGNO (x))))
 #endif
 	       /* We want to keep the stack, frame, and arg pointers
diff --git a/gcc/flow.c b/gcc/flow.c
index 0b6e78fecbf..2e2a79d42e8 100644
--- a/gcc/flow.c
+++ b/gcc/flow.c
@@ -5263,11 +5263,13 @@ mark_used_regs (pbi, x, cond, insn)
       break;
 
     case SUBREG:
+#ifdef CLASS_CANNOT_CHANGE_MODE
       if (GET_CODE (SUBREG_REG (x)) == REG
 	  && REGNO (SUBREG_REG (x)) >= FIRST_PSEUDO_REGISTER
-	  && (GET_MODE_SIZE (GET_MODE (x))
-	      != GET_MODE_SIZE (GET_MODE (SUBREG_REG (x)))))
-	REG_CHANGES_SIZE (REGNO (SUBREG_REG (x))) = 1;
+	  && CLASS_CANNOT_CHANGE_MODE_P (GET_MODE (x),
+					 GET_MODE (SUBREG_REG (x))))
+	REG_CHANGES_MODE (REGNO (SUBREG_REG (x))) = 1;
+#endif
 
       /* While we're here, optimize this case.  */
       x = SUBREG_REG (x);
@@ -5310,12 +5312,14 @@ mark_used_regs (pbi, x, cond, insn)
 	       || GET_CODE (testreg) == SIGN_EXTRACT
 	       || GET_CODE (testreg) == SUBREG)
 	  {
+#ifdef CLASS_CANNOT_CHANGE_MODE
 	    if (GET_CODE (testreg) == SUBREG
 		&& GET_CODE (SUBREG_REG (testreg)) == REG
 		&& REGNO (SUBREG_REG (testreg)) >= FIRST_PSEUDO_REGISTER
-		&& (GET_MODE_SIZE (GET_MODE (testreg))
-		    != GET_MODE_SIZE (GET_MODE (SUBREG_REG (testreg)))))
-	      REG_CHANGES_SIZE (REGNO (SUBREG_REG (testreg))) = 1;
+		&& CLASS_CANNOT_CHANGE_MODE_P (GET_MODE (SUBREG_REG (testreg)),
+					       GET_MODE (testreg)))
+	      REG_CHANGES_MODE (REGNO (SUBREG_REG (testreg))) = 1;
+#endif
 
 	    /* Modifying a single register in an alternate mode
 	       does not use any of the old value.  But these other
diff --git a/gcc/global.c b/gcc/global.c
index 3c615538643..4ad1e1967fb 100644
--- a/gcc/global.c
+++ b/gcc/global.c
@@ -999,10 +999,10 @@ find_reg (num, losers, alt_regs_p, accept_call_clobbered, retrying)
 
   IOR_HARD_REG_SET (used1, allocno[num].hard_reg_conflicts);
 
-#ifdef CLASS_CANNOT_CHANGE_SIZE
-  if (REG_CHANGES_SIZE (allocno[num].reg))
+#ifdef CLASS_CANNOT_CHANGE_MODE
+  if (REG_CHANGES_MODE (allocno[num].reg))
     IOR_HARD_REG_SET (used1,
-		      reg_class_contents[(int) CLASS_CANNOT_CHANGE_SIZE]);
+		      reg_class_contents[(int) CLASS_CANNOT_CHANGE_MODE]);
 #endif
 
   /* Try each hard reg to see if it fits.  Do this in two passes.
@@ -1189,10 +1189,10 @@ find_reg (num, losers, alt_regs_p, accept_call_clobbered, retrying)
 	      /* Don't use a reg no good for this pseudo.  */
 	      && ! TEST_HARD_REG_BIT (used2, regno)
 	      && HARD_REGNO_MODE_OK (regno, mode)
-#ifdef CLASS_CANNOT_CHANGE_SIZE
-	      && ! (REG_CHANGES_SIZE (allocno[num].reg)
+#ifdef CLASS_CANNOT_CHANGE_MODE
+	      && ! (REG_CHANGES_MODE (allocno[num].reg)
 		    && (TEST_HARD_REG_BIT
-			(reg_class_contents[(int) CLASS_CANNOT_CHANGE_SIZE],
+			(reg_class_contents[(int) CLASS_CANNOT_CHANGE_MODE],
 			 regno)))
 #endif
 	      )
diff --git a/gcc/local-alloc.c b/gcc/local-alloc.c
index bd6492980ea..e2c00bf8dec 100644
--- a/gcc/local-alloc.c
+++ b/gcc/local-alloc.c
@@ -140,10 +140,10 @@ struct qty
 
   short phys_reg;
 
-  /* Nonzero if this quantity has been used in a SUBREG that changes
-     its size.  */
+  /* Nonzero if this quantity has been used in a SUBREG in some
+     way that is illegal.  */
 
-  char changes_size;
+  char changes_mode;
 
 };
 
@@ -301,7 +301,7 @@ alloc_qty (regno, mode, size, birth)
   qty[qtyno].min_class = reg_preferred_class (regno);
   qty[qtyno].alternate_class = reg_alternate_class (regno);
   qty[qtyno].n_refs = REG_N_REFS (regno);
-  qty[qtyno].changes_size = REG_CHANGES_SIZE (regno);
+  qty[qtyno].changes_mode = REG_CHANGES_MODE (regno);
 }
 
 /* Main entry point of this file.  */
@@ -1795,8 +1795,8 @@ update_qty_class (qtyno, reg)
   if (reg_class_subset_p (rclass, qty[qtyno].alternate_class))
     qty[qtyno].alternate_class = rclass;
 
-  if (REG_CHANGES_SIZE (reg))
-    qty[qtyno].changes_size = 1;
+  if (REG_CHANGES_MODE (reg))
+    qty[qtyno].changes_mode = 1;
 }
 
 /* Handle something which alters the value of an rtx REG.
@@ -1997,10 +1997,10 @@ find_free_reg (class, mode, qtyno, accept_call_clobbered, just_try_suggested,
   SET_HARD_REG_BIT (used, FRAME_POINTER_REGNUM);
 #endif
 
-#ifdef CLASS_CANNOT_CHANGE_SIZE
-  if (qty[qtyno].changes_size)
+#ifdef CLASS_CANNOT_CHANGE_MODE
+  if (qty[qtyno].changes_mode)
     IOR_HARD_REG_SET (used,
-		      reg_class_contents[(int) CLASS_CANNOT_CHANGE_SIZE]);
+		      reg_class_contents[(int) CLASS_CANNOT_CHANGE_MODE]);
 #endif
 
   /* Normally, the registers that can be used for the first register in
diff --git a/gcc/recog.c b/gcc/recog.c
index 556f9f98b29..3b7dab35ff2 100644
--- a/gcc/recog.c
+++ b/gcc/recog.c
@@ -1003,13 +1003,13 @@ register_operand (op, mode)
       if (! reload_completed && GET_CODE (SUBREG_REG (op)) == MEM)
 	return general_operand (op, mode);
 
-#ifdef CLASS_CANNOT_CHANGE_SIZE
+#ifdef CLASS_CANNOT_CHANGE_MODE
       if (GET_CODE (SUBREG_REG (op)) == REG
 	  && REGNO (SUBREG_REG (op)) < FIRST_PSEUDO_REGISTER
-	  && TEST_HARD_REG_BIT (reg_class_contents[(int) CLASS_CANNOT_CHANGE_SIZE],
-				REGNO (SUBREG_REG (op)))
-	  && (GET_MODE_SIZE (mode)
-	      != GET_MODE_SIZE (GET_MODE (SUBREG_REG (op))))
+	  && (TEST_HARD_REG_BIT
+	      (reg_class_contents[(int) CLASS_CANNOT_CHANGE_MODE],
+	       REGNO (SUBREG_REG (op))))
+	  && CLASS_CANNOT_CHANGE_MODE_P (mode, GET_MODE (SUBREG_REG (op)))
 	  && GET_MODE_CLASS (GET_MODE (SUBREG_REG (op))) != MODE_COMPLEX_INT
 	  && GET_MODE_CLASS (GET_MODE (SUBREG_REG (op))) != MODE_COMPLEX_FLOAT)
 	return 0;
diff --git a/gcc/regclass.c b/gcc/regclass.c
index a0781833c67..eb909d195a5 100644
--- a/gcc/regclass.c
+++ b/gcc/regclass.c
@@ -203,18 +203,20 @@ static char *in_inc_dec;
 
 #endif /* FORBIDDEN_INC_DEC_CLASSES */
 
-#ifdef CLASS_CANNOT_CHANGE_SIZE
+#ifdef CLASS_CANNOT_CHANGE_MODE
 
 /* These are the classes containing only registers that can be used in
-   a SUBREG expression that changes the size of the register.  */
+   a SUBREG expression that changes the mode of the register in some
+   way that is illegal.  */
 
-static int class_can_change_size[N_REG_CLASSES];
+static int class_can_change_mode[N_REG_CLASSES];
 
-/* Registers, including pseudos, which change size.  */
+/* Registers, including pseudos, which change modes in some way that
+   is illegal.  */
 
-static regset reg_changes_size;
+static regset reg_changes_mode;
 
-#endif /* CLASS_CANNOT_CHANGE_SIZE */
+#endif /* CLASS_CANNOT_CHANGE_MODE */
 
 #ifdef HAVE_SECONDARY_RELOADS
 
@@ -458,21 +460,21 @@ init_reg_sets_1 ()
 	  may_move_out_cost[i][j] = cost;
       }
 
-#ifdef CLASS_CANNOT_CHANGE_SIZE
+#ifdef CLASS_CANNOT_CHANGE_MODE
   {
     HARD_REG_SET c;
-    COMPL_HARD_REG_SET (c, reg_class_contents[CLASS_CANNOT_CHANGE_SIZE]);
+    COMPL_HARD_REG_SET (c, reg_class_contents[CLASS_CANNOT_CHANGE_MODE]);
       
     for (i = 0; i < N_REG_CLASSES; i++)
       {
 	GO_IF_HARD_REG_SUBSET (reg_class_contents[i], c, ok_class);
-	class_can_change_size [i] = 0;
+	class_can_change_mode [i] = 0;
 	continue;
       ok_class:
-	class_can_change_size [i] = 1;
+	class_can_change_mode [i] = 1;
       }
     }
-#endif /* CLASS_CANNOT_CHANGE_SIZE */
+#endif /* CLASS_CANNOT_CHANGE_MODE */
 }
 
 /* Compute the table of register modes.
@@ -860,10 +862,10 @@ record_operand_costs (insn, op_costs, reg_pref)
       if (GET_CODE (recog_data.operand[i]) == SUBREG)
 	{
 	  rtx inner = SUBREG_REG (recog_data.operand[i]);
-#ifdef CLASS_CANNOT_CHANGE_SIZE
-	  if (GET_MODE_SIZE (modes[i]) != GET_MODE_SIZE (GET_MODE (inner))
-	      && GET_CODE (inner) == REG)
-	    SET_REGNO_REG_SET (reg_changes_size, REGNO (inner));
+#ifdef CLASS_CANNOT_CHANGE_MODE
+	  if (GET_CODE (inner) == REG
+	      && CLASS_CANNOT_CHANGE_MODE_P (modes[i], GET_MODE (inner)))
+	    SET_REGNO_REG_SET (reg_changes_mode, REGNO (inner));
 #endif
 	  recog_data.operand[i] = inner;
 	}
@@ -1048,8 +1050,8 @@ regclass (f, nregs, dump)
 
   costs = (struct costs *) xmalloc (nregs * sizeof (struct costs));
 
-#ifdef CLASS_CANNOT_CHANGE_SIZE
-  reg_changes_size = BITMAP_XMALLOC();
+#ifdef CLASS_CANNOT_CHANGE_MODE
+  reg_changes_mode = BITMAP_XMALLOC();
 #endif  
 
 #ifdef FORBIDDEN_INC_DEC_CLASSES
@@ -1190,9 +1192,9 @@ regclass (f, nregs, dump)
 #ifdef FORBIDDEN_INC_DEC_CLASSES
 		  || (in_inc_dec[i] && forbidden_inc_dec_class[class])
 #endif
-#ifdef CLASS_CANNOT_CHANGE_SIZE
-		  || (REGNO_REG_SET_P (reg_changes_size, i)
-		      && ! class_can_change_size [class])
+#ifdef CLASS_CANNOT_CHANGE_MODE
+		  || (REGNO_REG_SET_P (reg_changes_mode, i)
+		      && ! class_can_change_mode [class])
 #endif
 		  )
 		;
@@ -1220,9 +1222,9 @@ regclass (f, nregs, dump)
 #ifdef FORBIDDEN_INC_DEC_CLASSES
 		  && ! (in_inc_dec[i] && forbidden_inc_dec_class[class])
 #endif
-#ifdef CLASS_CANNOT_CHANGE_SIZE
-		  && ! (REGNO_REG_SET_P (reg_changes_size, i)
-			&& ! class_can_change_size [class])
+#ifdef CLASS_CANNOT_CHANGE_MODE
+		  && ! (REGNO_REG_SET_P (reg_changes_mode, i)
+			&& ! class_can_change_mode [class])
 #endif
 		  )
 		alt = reg_class_subunion[(int) alt][class];
@@ -1256,8 +1258,8 @@ regclass (f, nregs, dump)
 #ifdef FORBIDDEN_INC_DEC_CLASSES
   free (in_inc_dec);
 #endif
-#ifdef CLASS_CANNOT_CHANGE_SIZE
-  BITMAP_XFREE (reg_changes_size);
+#ifdef CLASS_CANNOT_CHANGE_MODE
+  BITMAP_XFREE (reg_changes_mode);
 #endif
   free (costs);
 }
diff --git a/gcc/regs.h b/gcc/regs.h
index 9c1b886d864..c219ecc4e20 100644
--- a/gcc/regs.h
+++ b/gcc/regs.h
@@ -55,7 +55,8 @@ typedef struct reg_info_def
   int live_length;		/* # of instructions (REG n) is live */
   int calls_crossed;		/* # of calls (REG n) is live across */
   int basic_block;		/* # of basic blocks (REG n) is used in */
-  char changes_size;		/* whether (SUBREG (REG n)) changes size */
+  char changes_mode;		/* whether (SUBREG (REG n)) exists and 
+				   is illegal.  */
 } reg_info;
 
 extern varray_type reg_n_info;
@@ -80,10 +81,11 @@ extern varray_type reg_n_info;
 #define REG_N_DEATHS(N) (VARRAY_REG (reg_n_info, N)->deaths)
 
 /* Indexed by N; says whether a pseudo register N was ever used
-   within a SUBREG that changes the size of the reg.  Some machines prohibit
-   such objects to be in certain (usually floating-point) registers.  */
+   within a SUBREG that changes the mode of the reg in some way
+   that is illegal for a given class (usually floating-point)
+   of registers.  */
 
-#define REG_CHANGES_SIZE(N) (VARRAY_REG (reg_n_info, N)->changes_size)
+#define REG_CHANGES_MODE(N) (VARRAY_REG (reg_n_info, N)->changes_mode)
 
 /* Get the number of consecutive words required to hold pseudo-reg N.  */
 
diff --git a/gcc/reload.c b/gcc/reload.c
index 0a6d14cd7e5..ce4811a7b40 100644
--- a/gcc/reload.c
+++ b/gcc/reload.c
@@ -908,8 +908,8 @@ push_reload (in, out, inloc, outloc, class,
 
   if (in != 0 && GET_CODE (in) == SUBREG
       && (SUBREG_WORD (in) == 0 || strict_low)
-#ifdef CLASS_CANNOT_CHANGE_SIZE
-      && class != CLASS_CANNOT_CHANGE_SIZE
+#ifdef CLASS_CANNOT_CHANGE_MODE
+      && class != CLASS_CANNOT_CHANGE_MODE
 #endif
       && (CONSTANT_P (SUBREG_REG (in))
 	  || GET_CODE (SUBREG_REG (in)) == PLUS
@@ -958,14 +958,14 @@ push_reload (in, out, inloc, outloc, class,
 						SUBREG_REG (in))
 		  == NO_REGS))
 #endif
-#ifdef CLASS_CANNOT_CHANGE_SIZE
+#ifdef CLASS_CANNOT_CHANGE_MODE
 	  || (GET_CODE (SUBREG_REG (in)) == REG
 	      && REGNO (SUBREG_REG (in)) < FIRST_PSEUDO_REGISTER
 	      && (TEST_HARD_REG_BIT
-		  (reg_class_contents[(int) CLASS_CANNOT_CHANGE_SIZE],
+		  (reg_class_contents[(int) CLASS_CANNOT_CHANGE_MODE],
 		   REGNO (SUBREG_REG (in))))
-	      && (GET_MODE_SIZE (GET_MODE (SUBREG_REG (in)))
-		  != GET_MODE_SIZE (inmode)))
+	      && CLASS_CANNOT_CHANGE_MODE_P (GET_MODE (SUBREG_REG (in)),
+					     inmode))
 #endif
 	  ))
     {
@@ -1026,8 +1026,8 @@ push_reload (in, out, inloc, outloc, class,
      and in that case the constraint should label it input-output.)  */
   if (out != 0 && GET_CODE (out) == SUBREG
       && (SUBREG_WORD (out) == 0 || strict_low)
-#ifdef CLASS_CANNOT_CHANGE_SIZE
-      && class != CLASS_CANNOT_CHANGE_SIZE
+#ifdef CLASS_CANNOT_CHANGE_MODE
+      && class != CLASS_CANNOT_CHANGE_MODE
 #endif
       && (CONSTANT_P (SUBREG_REG (out))
 	  || strict_low
@@ -1063,14 +1063,14 @@ push_reload (in, out, inloc, outloc, class,
 						 SUBREG_REG (out))
 		  == NO_REGS))
 #endif
-#ifdef CLASS_CANNOT_CHANGE_SIZE
+#ifdef CLASS_CANNOT_CHANGE_MODE
 	  || (GET_CODE (SUBREG_REG (out)) == REG
 	      && REGNO (SUBREG_REG (out)) < FIRST_PSEUDO_REGISTER
 	      && (TEST_HARD_REG_BIT
-		  (reg_class_contents[(int) CLASS_CANNOT_CHANGE_SIZE],
+		  (reg_class_contents[(int) CLASS_CANNOT_CHANGE_MODE],
 		   REGNO (SUBREG_REG (out))))
-	      && (GET_MODE_SIZE (GET_MODE (SUBREG_REG (out)))
-		  != GET_MODE_SIZE (outmode)))
+	      && CLASS_CANNOT_CHANGE_MODE_P (GET_MODE (SUBREG_REG (out)),
+					     outmode))
 #endif
 	  ))
     {
diff --git a/gcc/reload1.c b/gcc/reload1.c
index 6f73aeaf13a..4949b89362f 100644
--- a/gcc/reload1.c
+++ b/gcc/reload1.c
@@ -5305,20 +5305,25 @@ choose_reload_regs (chain)
 		{
 		  enum reg_class class = rld[r].class, last_class;
 		  rtx last_reg = reg_last_reload_reg[regno];
+		  enum machine_mode need_mode;
 
 		  i = REGNO (last_reg) + word;
 		  last_class = REGNO_REG_CLASS (i);
+
+		  need_mode = smallest_mode_for_size ((word+1) * UNITS_PER_WORD,
+						      GET_MODE_CLASS (mode));
+
 		  if (
-#ifdef CLASS_CANNOT_CHANGE_SIZE
+#ifdef CLASS_CANNOT_CHANGE_MODE
 		      (TEST_HARD_REG_BIT
-		       (reg_class_contents[CLASS_CANNOT_CHANGE_SIZE], i)
-		       ? (GET_MODE_SIZE (GET_MODE (last_reg))
-			  == GET_MODE_SIZE (mode) + word * UNITS_PER_WORD)
+		       (reg_class_contents[(int) CLASS_CANNOT_CHANGE_MODE], i)
+		       ? ! CLASS_CANNOT_CHANGE_MODE_P (GET_MODE (last_reg), 
+						       need_mode)
 		       : (GET_MODE_SIZE (GET_MODE (last_reg))
-			  >= GET_MODE_SIZE (mode) + word * UNITS_PER_WORD))
+			  >= GET_MODE_SIZE (need_mode)))
 #else
 		      (GET_MODE_SIZE (GET_MODE (last_reg))
-		       >= GET_MODE_SIZE (mode) + word * UNITS_PER_WORD)
+		       >= GET_MODE_SIZE (need_mode))
 #endif
 		      && reg_reloaded_contents[i] == regno
 		      && TEST_HARD_REG_BIT (reg_reloaded_valid, i)
diff --git a/gcc/tm.texi b/gcc/tm.texi
index 4648778daf9..90e5e908fee 100644
--- a/gcc/tm.texi
+++ b/gcc/tm.texi
@@ -2088,17 +2088,25 @@ should be the maximum value of @code{HARD_REGNO_NREGS (@var{regno},
 This macro helps control the handling of multiple-word values
 in the reload pass.
 
-@item CLASS_CANNOT_CHANGE_SIZE
-If defined, a C expression for a class that contains registers which the
-compiler must always access in a mode that is the same size as the mode
-in which it loaded the register.
+@item CLASS_CANNOT_CHANGE_MODE
+If defined, a C expression for a class that contains registers for
+which the compiler may not change modes arbitrarily.
+
+@item CLASS_CANNOT_CHANGE_MODE_P(@var{from}, @var{to})
+A C expression that is true if, for a register in
+@code{CLASS_CANNOT_CHANGE_MODE}, the requested mode punning is illegal.
 
 For the example, loading 32-bit integer or floating-point objects into
 floating-point registers on the Alpha extends them to 64-bits.
 Therefore loading a 64-bit object and then storing it as a 32-bit object
 does not store the low-order 32-bits, as would be the case for a normal
-register.  Therefore, @file{alpha.h} defines this macro as
-@code{FLOAT_REGS}.
+register.  Therefore, @file{alpha.h} defines @code{CLASS_CANNOT_CHANGE_MODE}
+as @code{FLOAT_REGS} and @code{CLASS_CANNOT_CHANGE_MODE_P} restricts
+mode changes to same-size modes.
+
+Compare this to IA-64, which extends floating-point values to 82-bits,
+and stores 64-bit integers in a different format than 64-bit doubles.
+Therefore @code{CLASS_CANNOT_CHANGE_MODE_P} is always true.
 @end table
 
 Three other special macros describe which operands fit which constraint