PR combine/110867 Fix narrow comparison of memory and constant
Checks
Commit Message
In certain cases a constant may not fit into the mode used to perform a
comparison. This may be the case for sign-extended constants which are
used during an unsigned comparison as e.g. in
(set (reg:CC 100 cc)
(compare:CC (mem:SI (reg/v/f:SI 115 [ a ]) [1 *a_4(D)+0 S4 A64])
(const_int -2147483648 [0xffffffff80000000])))
Fixed by ensuring that the constant fits into comparison mode.
Furthermore, on some targets as e.g. sparc the constant used in a
comparison is chopped off before combine which leads to failing test
cases (see PR 110869). Fixed by not requiring that the source mode has
to be DImode, and excluding sparc from the last two test cases entirely
since there the constant cannot be further reduced.
According to PR 110867 and 110869 this patch resolves bootstrap problems
on armv8l and sparc. While writing this, bootstrap+regtest are still
running on x64 and s390x. Assuming they pass, ok for mainline?
gcc/ChangeLog:
PR combine/110867
* combine.cc (simplify_compare_const): Try the optimization only
in case the constant fits into the comparison mode.
gcc/testsuite/ChangeLog:
PR combine/110869
* gcc.dg/cmp-mem-const-1.c: Relax mode for constant.
* gcc.dg/cmp-mem-const-2.c: Relax mode for constant.
* gcc.dg/cmp-mem-const-3.c: Relax mode for constant.
* gcc.dg/cmp-mem-const-4.c: Relax mode for constant.
* gcc.dg/cmp-mem-const-5.c: Exclude sparc since here the
constant is already reduced.
* gcc.dg/cmp-mem-const-6.c: Exclude sparc since here the
constant is already reduced.
---
gcc/combine.cc | 4 ++++
gcc/testsuite/gcc.dg/cmp-mem-const-1.c | 2 +-
gcc/testsuite/gcc.dg/cmp-mem-const-2.c | 2 +-
gcc/testsuite/gcc.dg/cmp-mem-const-3.c | 2 +-
gcc/testsuite/gcc.dg/cmp-mem-const-4.c | 2 +-
gcc/testsuite/gcc.dg/cmp-mem-const-5.c | 4 ++--
gcc/testsuite/gcc.dg/cmp-mem-const-6.c | 4 ++--
7 files changed, 12 insertions(+), 8 deletions(-)
Comments
On 8/2/23 07:49, Stefan Schulze Frielinghaus via Gcc-patches wrote:
> In certain cases a constant may not fit into the mode used to perform a
> comparison. This may be the case for sign-extended constants which are
> used during an unsigned comparison as e.g. in
>
> (set (reg:CC 100 cc)
> (compare:CC (mem:SI (reg/v/f:SI 115 [ a ]) [1 *a_4(D)+0 S4 A64])
> (const_int -2147483648 [0xffffffff80000000])))
>
> Fixed by ensuring that the constant fits into comparison mode.
>
> Furthermore, on some targets as e.g. sparc the constant used in a
> comparison is chopped off before combine which leads to failing test
> cases (see PR 110869). Fixed by not requiring that the source mode has
> to be DImode, and excluding sparc from the last two test cases entirely
> since there the constant cannot be further reduced.
>
> According to PR 110867 and 110869 this patch resolves bootstrap problems
> on armv8l and sparc. While writing this, bootstrap+regtest are still
> running on x64 and s390x. Assuming they pass, ok for mainline?
>
> gcc/ChangeLog:
>
> PR combine/110867
> * combine.cc (simplify_compare_const): Try the optimization only
> in case the constant fits into the comparison mode.
>
> gcc/testsuite/ChangeLog:
>
> PR combine/110869
> * gcc.dg/cmp-mem-const-1.c: Relax mode for constant.
> * gcc.dg/cmp-mem-const-2.c: Relax mode for constant.
> * gcc.dg/cmp-mem-const-3.c: Relax mode for constant.
> * gcc.dg/cmp-mem-const-4.c: Relax mode for constant.
> * gcc.dg/cmp-mem-const-5.c: Exclude sparc since here the
> constant is already reduced.
> * gcc.dg/cmp-mem-const-6.c: Exclude sparc since here the
> constant is already reduced.
OK
jeff
@@ -11998,11 +11998,15 @@ simplify_compare_const (enum rtx_code code, machine_mode mode,
x0 >= 0x40. */
if ((code == LEU || code == LTU || code == GEU || code == GTU)
&& is_a <scalar_int_mode> (GET_MODE (op0), &int_mode)
+ && HWI_COMPUTABLE_MODE_P (int_mode)
&& MEM_P (op0)
&& !MEM_VOLATILE_P (op0)
/* The optimization makes only sense for constants which are big enough
so that we have a chance to chop off something at all. */
&& (unsigned HOST_WIDE_INT) const_op > 0xff
+ /* Bail out, if the constant does not fit into INT_MODE. */
+ && (unsigned HOST_WIDE_INT) const_op
+ < ((HOST_WIDE_INT_1U << (GET_MODE_PRECISION (int_mode) - 1) << 1) - 1)
/* Ensure that we do not overflow during normalization. */
&& (code != GTU || (unsigned HOST_WIDE_INT) const_op < HOST_WIDE_INT_M1U))
{
@@ -1,6 +1,6 @@
/* { dg-do compile { target { lp64 } } } */
/* { dg-options "-O1 -fdump-rtl-combine-details" } */
-/* { dg-final { scan-rtl-dump "narrow comparison from mode DI to QI" "combine" } } */
+/* { dg-final { scan-rtl-dump "narrow comparison from mode .I to QI" "combine" } } */
typedef __UINT64_TYPE__ uint64_t;
@@ -1,6 +1,6 @@
/* { dg-do compile { target { lp64 } } } */
/* { dg-options "-O1 -fdump-rtl-combine-details" } */
-/* { dg-final { scan-rtl-dump "narrow comparison from mode DI to QI" "combine" } } */
+/* { dg-final { scan-rtl-dump "narrow comparison from mode .I to QI" "combine" } } */
typedef __UINT64_TYPE__ uint64_t;
@@ -1,6 +1,6 @@
/* { dg-do compile { target { lp64 } } } */
/* { dg-options "-O1 -fdump-rtl-combine-details" } */
-/* { dg-final { scan-rtl-dump "narrow comparison from mode DI to HI" "combine" } } */
+/* { dg-final { scan-rtl-dump "narrow comparison from mode .I to HI" "combine" } } */
typedef __UINT64_TYPE__ uint64_t;
@@ -1,6 +1,6 @@
/* { dg-do compile { target { lp64 } } } */
/* { dg-options "-O1 -fdump-rtl-combine-details" } */
-/* { dg-final { scan-rtl-dump "narrow comparison from mode DI to HI" "combine" } } */
+/* { dg-final { scan-rtl-dump "narrow comparison from mode .I to HI" "combine" } } */
typedef __UINT64_TYPE__ uint64_t;
@@ -1,6 +1,6 @@
-/* { dg-do compile { target { lp64 } } } */
+/* { dg-do compile { target { lp64 } && ! target { sparc*-*-* } } } */
/* { dg-options "-O1 -fdump-rtl-combine-details" } */
-/* { dg-final { scan-rtl-dump "narrow comparison from mode DI to SI" "combine" } } */
+/* { dg-final { scan-rtl-dump "narrow comparison from mode .I to SI" "combine" } } */
typedef __UINT64_TYPE__ uint64_t;
@@ -1,6 +1,6 @@
-/* { dg-do compile { target { lp64 } } } */
+/* { dg-do compile { target { lp64 } && ! target { sparc*-*-* } } } */
/* { dg-options "-O1 -fdump-rtl-combine-details" } */
-/* { dg-final { scan-rtl-dump "narrow comparison from mode DI to SI" "combine" } } */
+/* { dg-final { scan-rtl-dump "narrow comparison from mode .I to SI" "combine" } } */
typedef __UINT64_TYPE__ uint64_t;