diff mbox series

arm: Fix REVERSIBLE_CC_MODE [PR110796...]

Message ID 20250313082244.1771233-1-christophe.lyon@linaro.org
State New
Headers
Series arm: Fix REVERSIBLE_CC_MODE [PR110796...] |

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Commit Message

Christophe Lyon March 13, 2025, 8:22 a.m. UTC 
  Since we have vcmp and vcmpe instructions (vcmpe raises an "Invalid
Operation" exception in presence of a NaN operand), we need to tell
the compiler it is not safe to reverse comparisons of floating-point
arguments.

On armv8-m.main+dsp+fp (cortex-m33):
PASS: gcc.dg/torture/builtin-iseqsig-1.c
at -O1, -O2, -O3, -Os

On armv8.1-m.main+mve.fp+fp.dp (cortex-m55):
PASS: gcc.dg/torture/builtin-iseqsig-1.c
PASS: gcc.dg/torture/builtin-iseqsig-2.c
PASS: gcc.dg/torture/builtin-iseqsig-3.c
at -O1, -O2, -O3, -Os

On armv7e-m+fp.dp (cortex-m7):
PASS: gcc.dg/torture/builtin-iseqsig-1.c
PASS: gcc.dg/torture/builtin-iseqsig-2.c
PASS: gcc.dg/torture/builtin-iseqsig-3.c
PASS: gcc.dg/torture/pr82692.c
at -O1, -O2, -O3, -Os

On armv8-a+simd:
PASS: gcc.dg/torture/builtin-iseqsig-1.c
PASS: gcc.dg/torture/builtin-iseqsig-2.c
PASS: gcc.dg/torture/builtin-iseqsig-3.c
PASS: gfortran.dg/ieee/comparisons_3.F90
at -Os (they already passed at other optimization levels)

	gcc/
	PR target/110796
	PR target/118446
	* config/arm/arm.h (REVERSIBLE_CC_MODE): Take floating-point modes
	into account.
---
 gcc/config/arm/arm.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

Comments

Richard Earnshaw (lists) March 13, 2025, 5:21 p.m. UTC | #1 
On 13/03/2025 08:22, Christophe Lyon wrote:
> Since we have vcmp and vcmpe instructions (vcmpe raises an "Invalid
> Operation" exception in presence of a NaN operand), we need to tell
> the compiler it is not safe to reverse comparisons of floating-point
> arguments.
> 
> On armv8-m.main+dsp+fp (cortex-m33):
> PASS: gcc.dg/torture/builtin-iseqsig-1.c
> at -O1, -O2, -O3, -Os
> 
> On armv8.1-m.main+mve.fp+fp.dp (cortex-m55):
> PASS: gcc.dg/torture/builtin-iseqsig-1.c
> PASS: gcc.dg/torture/builtin-iseqsig-2.c
> PASS: gcc.dg/torture/builtin-iseqsig-3.c
> at -O1, -O2, -O3, -Os
> 
> On armv7e-m+fp.dp (cortex-m7):
> PASS: gcc.dg/torture/builtin-iseqsig-1.c
> PASS: gcc.dg/torture/builtin-iseqsig-2.c
> PASS: gcc.dg/torture/builtin-iseqsig-3.c
> PASS: gcc.dg/torture/pr82692.c
> at -O1, -O2, -O3, -Os
> 
> On armv8-a+simd:
> PASS: gcc.dg/torture/builtin-iseqsig-1.c
> PASS: gcc.dg/torture/builtin-iseqsig-2.c
> PASS: gcc.dg/torture/builtin-iseqsig-3.c
> PASS: gfortran.dg/ieee/comparisons_3.F90
> at -Os (they already passed at other optimization levels)
> 
> 	gcc/
> 	PR target/110796
> 	PR target/118446
> 	* config/arm/arm.h (REVERSIBLE_CC_MODE): Take floating-point modes
> 	into account.
> ---
>  gcc/config/arm/arm.h | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/gcc/config/arm/arm.h b/gcc/config/arm/arm.h
> index 8472b756127..3c9c7c795cb 100644
> --- a/gcc/config/arm/arm.h
> +++ b/gcc/config/arm/arm.h
> @@ -2257,7 +2257,10 @@ extern int making_const_table;
>  
>  #define SELECT_CC_MODE(OP, X, Y)  arm_select_cc_mode (OP, X, Y)
>  
> -#define REVERSIBLE_CC_MODE(MODE) 1
> +/* Having an integer comparison mode guarantees that we can use
> +   reverse_condition, but the usual restrictions apply to floating-point
> +   comparisons.  */
> +#define REVERSIBLE_CC_MODE(MODE) ((MODE) != CCFPmode && (MODE) != CCFPEmode)
>  
>  #define REVERSE_CONDITION(CODE,MODE) \
>    (((MODE) == CCFPmode || (MODE) == CCFPEmode) \

I'd like to understand the impact of this for conditional execution when the result comes from a floating-point comparison.  Adding support for non-reversable conditions would involve adding a substantial number of patterns to the machine description.

R.
diff mbox series

Patch

diff --git a/gcc/config/arm/arm.h b/gcc/config/arm/arm.h
index 8472b756127..3c9c7c795cb 100644
--- a/gcc/config/arm/arm.h
+++ b/gcc/config/arm/arm.h
@@ -2257,7 +2257,10 @@  extern int making_const_table;
 
 #define SELECT_CC_MODE(OP, X, Y)  arm_select_cc_mode (OP, X, Y)
 
-#define REVERSIBLE_CC_MODE(MODE) 1
+/* Having an integer comparison mode guarantees that we can use
+   reverse_condition, but the usual restrictions apply to floating-point
+   comparisons.  */
+#define REVERSIBLE_CC_MODE(MODE) ((MODE) != CCFPmode && (MODE) != CCFPEmode)
 
 #define REVERSE_CONDITION(CODE,MODE) \
   (((MODE) == CCFPmode || (MODE) == CCFPEmode) \