combine: Convert subreg-of-lshiftrt to zero_extract properly (PR78390)

r242414, for PR77881, introduces some bugs (PR78390, PR78438, PR78477).
It all has the same root cause: that patch makes combine convert every
lowpart subreg of a logical shift right to a zero_extract.  This cannot
work at all if it is not a constant shift, and it has to be a bit more
careful exactly which bits it extracts.


	PR target/77881
	PR bootstrap/78390
	PR target/78438
	PR bootstrap/78477
	* combine.c (make_compound_operation_int): Do not convert a subreg of
	a non-constant logical shift right to a zero_extract.  Handle the case
	where some zero bits have been shifted into the range covered by that
	subreg.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@242757 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 6 insertions, 1 deletions

diff --git a/gcc/combine.c b/gcc/combine.c
index 93621bd02fb..ae25ef35ed9 100644
--- a/gcc/combine.c
+++ b/gcc/combine.c
@@ -8089,12 +8089,17 @@ make_compound_operation_int (machine_mode mode, rtx *x_ptr,
 	/* If the SUBREG is masking of a logical right shift,
 	   make an extraction.  */
 	if (GET_CODE (inner) == LSHIFTRT
+	    && CONST_INT_P (XEXP (inner, 1))
 	    && GET_MODE_SIZE (mode) < GET_MODE_SIZE (GET_MODE (inner))
 	    && subreg_lowpart_p (x))
 	  {
 	    new_rtx = make_compound_operation (XEXP (inner, 0), next_code);
+	    int width = GET_MODE_PRECISION (GET_MODE (inner))
+			- INTVAL (XEXP (inner, 1));
+	    if (width > mode_width)
+	      width = mode_width;
 	    new_rtx = make_extraction (mode, new_rtx, 0, XEXP (inner, 1),
-				       mode_width, 1, 0, in_code == COMPARE);
+				       width, 1, 0, in_code == COMPARE);
 	    break;
 	  }