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.
