2004-04-05 Paolo Bonzini <bonzini@gnu.org>

	* combine.c (RTL_HOOKS_GEN_LOWPART_NO_EMIT): Use
	gen_lowpart_for_combine.
	* cse.c (gen_lowpart_if_possible): Move...
	* rtlhooks.c (gen_lowpart_if_possible): ... here.  Also try
	gen_lowpart_SUBREG.
	(gen_lowpart_no_emit_general): Use it.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@97633 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 48 insertions, 4 deletions

diff --git a/gcc/rtlhooks.c b/gcc/rtlhooks.c
index dbe959308c0..9d5dafdff44 100644
--- a/gcc/rtlhooks.c
+++ b/gcc/rtlhooks.c
@@ -25,6 +25,7 @@ Software Foundation, 59 Temple Place - Suite 330, Boston, MA
 #include "rtl.h"
 #include "rtlhooks-def.h"
 #include "expr.h"
+#include "recog.h"
 
 
 /* For speed, we will copy the RTX hooks struct member-by-member
@@ -84,12 +85,11 @@ gen_lowpart_general (enum machine_mode mode, rtx x)
 rtx
 gen_lowpart_no_emit_general (enum machine_mode mode, rtx x)
 {
-  rtx result = gen_lowpart_common (mode, x);
+  rtx result = gen_lowpart_if_possible (mode, x);
   if (result)
     return result;
-  if (mode != GET_MODE (x) && GET_MODE (x) != VOIDmode)
-    return gen_lowpart_SUBREG (mode, x);
-  return x;
+  else
+    return x;
 }
 
 rtx
@@ -113,3 +113,47 @@ reg_nonzero_bits_general (rtx x ATTRIBUTE_UNUSED,
 {
   return NULL;
 }
+
+/* Assuming that X is an rtx (e.g., MEM, REG or SUBREG) for a fixed-point
+   number, return an rtx (MEM, SUBREG, or CONST_INT) that refers to the
+   least-significant part of X.
+   MODE specifies how big a part of X to return.
+
+   If the requested operation cannot be done, 0 is returned.
+
+   This is similar to gen_lowpart_general.  */
+
+rtx
+gen_lowpart_if_possible (enum machine_mode mode, rtx x)
+{
+  rtx result = gen_lowpart_common (mode, x);
+
+  if (result)
+    return result;
+  else if (MEM_P (x))
+    {
+      /* This is the only other case we handle.  */
+      int offset = 0;
+      rtx new;
+
+      if (WORDS_BIG_ENDIAN)
+	offset = (MAX (GET_MODE_SIZE (GET_MODE (x)), UNITS_PER_WORD)
+		  - MAX (GET_MODE_SIZE (mode), UNITS_PER_WORD));
+      if (BYTES_BIG_ENDIAN)
+	/* Adjust the address so that the address-after-the-data is
+	   unchanged.  */
+	offset -= (MIN (UNITS_PER_WORD, GET_MODE_SIZE (mode))
+		   - MIN (UNITS_PER_WORD, GET_MODE_SIZE (GET_MODE (x))));
+
+      new = adjust_address_nv (x, mode, offset);
+      if (! memory_address_p (mode, XEXP (new, 0)))
+	return 0;
+
+      return new;
+    }
+  else if (mode != GET_MODE (x) && GET_MODE (x) != VOIDmode)
+    return gen_lowpart_SUBREG (mode, x);
+  else
+    return 0;
+}
+