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simplify-rtx: Handle a != 0 ? -a : 0 [PR58195]

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The gimple (and generic) levels have this optmization since r12-2041-g7d6979197274a662da7bdc5.
It seems like a good idea to add a similar one to rtl just in case it is not caught at the
gimple level.

Note the loop case in csel-neg-1.c is not handled at the gimple level (even with phiopt turned back on),
this is because of casts to avoid signed integer overflow; a patch to fix this at the gimple level will be
submitted seperately.

Changes since v1:
* v2: Use `CONST0_RTX (mode)` instead of const0_rtx. Add csel-neg-2.c for float testcase which now passes.

Build and tested for aarch64-linux-gnu.

	PR rtl-optimization/58195

gcc/ChangeLog:

	* simplify-rtx.cc (simplify_context::simplify_ternary_operation): Handle
	`a != 0 ? -a : 0` and `a == 0 ? 0 : -a`.

gcc/testsuite/ChangeLog:

	* gcc.target/aarch64/csel-neg-1.c: New test.
	* gcc.target/aarch64/csel-neg-2.c: New test.

Signed-off-by: Andrew Pinski <quic_apinski@quicinc.com>
This commit is contained in:
Andrew Pinski 2024-10-20 10:44:14 -07:00
parent 2266e38cfd
commit 35bf490452
3 changed files with 72 additions and 0 deletions
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22
gcc/simplify-rtx.cc
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@ -6909,6 +6909,28 @@ simplify_context::simplify_ternary_operation (rtx_code code, machine_mode mode,
&& rtx_equal_p (XEXP (op0, 1), op1))))
return op2;
/* Convert a != 0 ? -a : 0 into "-a". */
if (GET_CODE (op0) == NE
&& ! side_effects_p (op0)
&& ! HONOR_NANS (mode)
&& ! HONOR_SIGNED_ZEROS (mode)
&& XEXP (op0, 1) == CONST0_RTX (mode)
&& op2 == CONST0_RTX (mode)
&& GET_CODE (op1) == NEG
&& rtx_equal_p (XEXP (op0, 0), XEXP (op1, 0)))
return op1;
/* Convert a == 0 ? 0 : -a into "-a". */
if (GET_CODE (op0) == EQ
&& ! side_effects_p (op0)
&& ! HONOR_NANS (mode)
&& ! HONOR_SIGNED_ZEROS (mode)
&& op1 == CONST0_RTX (mode)
&& XEXP (op0, 1) == CONST0_RTX (mode)
&& GET_CODE (op2) == NEG
&& rtx_equal_p (XEXP (op0, 0), XEXP (op2, 0)))
return op2;
/* Convert (!c) != {0,...,0} ? a : b into
c != {0,...,0} ? b : a for vector modes. */
if (VECTOR_MODE_P (GET_MODE (op1))

31
gcc/testsuite/gcc.target/aarch64/csel-neg-1.c Normal file
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@ -0,0 +1,31 @@
/* { dg-do compile } */
/* Disable phiopt as that will optimize away the `?:`,
want to test simplify-rtx */
/* { dg-options "-O2 -fno-ssa-phiopt" } */
/* PR rtl-optimization/58195 */
int a2(int input)
{
if (input == 0)
return 0;
return -input;
}
int a1(int input)
{
int t = -input;
return input == 0 ? 0 : t;
}
int a(int input)
{
int value = 0;
for(int n = input; n != 0; ++n)
++value;
return value;
}
/* There should be no comparison against 0 here, */
/* { dg-final { scan-assembler-not "cmp\t" } } */
/* { dg-final { scan-assembler "\tneg\t" } } */

19
gcc/testsuite/gcc.target/aarch64/csel-neg-2.c Normal file
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@ -0,0 +1,19 @@
/* { dg-do compile } */
/* Disable phiopt as that will optimize away the `?:`,
want to test simplify-rtx */
/* { dg-options "-O2 -ffast-math -fno-ssa-phiopt" } */
/* PR rtl-optimization/58195 */
float a2(float input)
{
if (input == 0)
return 0;
return -input;
}
/* There should be no comparison against 0 here, */
/* { dg-final { scan-assembler-not "\tfcmp\t" } } */
/* { dg-final { scan-assembler-not "\tfcsel\t" } } */
/* { dg-final { scan-assembler "\tfneg\t" } } */