[PATCH] combine: Fix handling of unsigned constants

[PATCH] combine: Fix handling of unsigned constants

[Stefan Schulze Frielinghaus]

If a CONST_INT represents an integer of a mode with fewer bits than in
HOST_WIDE_INT, then the integer is sign extended.  For those two
optimizations touched by this patch, the integers of interest have only
the most significant bit set w.r.t their mode, therefore, they were sign
extended.  Thus in order to get the integer of interest, we have to chop
off the high bits.

Bootstrapped and regtested on x64, powerpc64le, and s390.  Ok for
mainline?

gcc/ChangeLog:

	* combine.cc (simplify_compare_const): Fix handling of unsigned
	constants.
---
 gcc/combine.cc | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/gcc/combine.cc b/gcc/combine.cc
index 468b7fde911..80c4ff0fbaf 100644
--- a/gcc/combine.cc
+++ b/gcc/combine.cc
@@ -11923,7 +11923,7 @@ simplify_compare_const (enum rtx_code code, machine_mode mode,
       /* (unsigned) < 0x80000000 is equivalent to >= 0.  */
       else if (is_a <scalar_int_mode> (mode, &int_mode)
 	       && GET_MODE_PRECISION (int_mode) - 1 < HOST_BITS_PER_WIDE_INT
-	       && ((unsigned HOST_WIDE_INT) const_op
+	       && (((unsigned HOST_WIDE_INT) const_op & GET_MODE_MASK (int_mode))
 		   == HOST_WIDE_INT_1U << (GET_MODE_PRECISION (int_mode) - 1)))
 	{
 	  const_op = 0;
@@ -11962,7 +11962,7 @@ simplify_compare_const (enum rtx_code code, machine_mode mode,
       /* (unsigned) >= 0x80000000 is equivalent to < 0.  */
       else if (is_a <scalar_int_mode> (mode, &int_mode)
 	       && GET_MODE_PRECISION (int_mode) - 1 < HOST_BITS_PER_WIDE_INT
-	       && ((unsigned HOST_WIDE_INT) const_op
+	       && (((unsigned HOST_WIDE_INT) const_op & GET_MODE_MASK (int_mode))
 		   == HOST_WIDE_INT_1U << (GET_MODE_PRECISION (int_mode) - 1)))
 	{
 	  const_op = 0;
-- 
2.41.0

Re: [PATCH] combine: Fix handling of unsigned constants

[Jeff Law]

On 10/6/23 01:45, Stefan Schulze Frielinghaus wrote:
> If a CONST_INT represents an integer of a mode with fewer bits than in
> HOST_WIDE_INT, then the integer is sign extended.  For those two
> optimizations touched by this patch, the integers of interest have only
> the most significant bit set w.r.t their mode, therefore, they were sign
> extended.  Thus in order to get the integer of interest, we have to chop
> off the high bits.
> 
> Bootstrapped and regtested on x64, powerpc64le, and s390.  Ok for
> mainline?
> 
> gcc/ChangeLog:
> 
> 	* combine.cc (simplify_compare_const): Fix handling of unsigned
> 	constants.
OK
jeff