arm: Only reverse FP inequalities when -ffinite-math-only [PR110796...]

On Arm we have been failing to fully implement support for IEEE NaNs
in inequality comparisons because we have allowed reversing of
inequalities in a way that allows SELECT_CC_MODE to produce different
answers.  For example, the reverse of GT is UNLE, but if we pass these
two RTL codes to SELECT_CC_MODE, the former will return CCFPEmode,
while the latter CCFPmode.

It would be possible to allow fully reversible FPmodes, but to do so
would involve adding yet more RTL codes, something like NOT_GT and
NOT_UNLE, for the cases we cannot currently reverse.  NOT_GT would
then have the same condition code generation as UNLT, but the same
mode selection as GT.

In the mean time, we need to restrict REVERSIBLE_CC_MODE to
non-floating modes unless we are compiling with -ffinite-math-only.  In
that case we can continue to reverse the comparisons, but now we want
to always select CCFPmode as there's no need to consider the exception
raising cases.

	PR target/110796
	PR target/118446

gcc/ChangeLog:

	* config/arm/arm.h (REVERSIBLE_CC_MODE): FP modes are only
	reversible if flag_finite_math_only.
	* config/arm/arm.cc (arm_select_cc_mode): Return CCFPmode for all
	FP comparisons if flag_finite_math_only.

gcc/testsuite/ChangeLog:

	* gcc.target/arm/armv8_2-fp16-arith-1.c: Adjust due to no-longer
	emitting VCMPE when -ffast-math..

diff --git a/gcc/config/arm/arm.cc b/gcc/config/arm/arm.cc
index 670f487bcce3aba0f9b458eafa1362d54fa9ba5c..fccddb0e7bc5d2dd796bcb0d5027228478bd61f1 100644 (file)
--- a/gcc/config/arm/arm.cc
+++ b/gcc/config/arm/arm.cc
@@ -16218,7 +16218,9 @@ arm_select_cc_mode (enum rtx_code op, rtx x, rtx y)
        case LE:
        case GT:
        case GE:
-         return CCFPEmode;
+         return (flag_finite_math_only
+                 ? CCFPmode
+                 : CCFPEmode);
 
        default:
          gcc_unreachable ();

diff --git a/gcc/config/arm/arm.h b/gcc/config/arm/arm.h
index 8472b75612721b2de43b4efbf73afb554573faac..08d3f0dae3da47a4c417ae21bafe4f71c8950052 100644 (file)
--- a/gcc/config/arm/arm.h
+++ b/gcc/config/arm/arm.h
@@ -2257,7 +2257,11 @@ 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
+/* Floating-point modes cannot be reversed unless we don't care about
+   NaNs.  */
+#define REVERSIBLE_CC_MODE(MODE)                       \
+  (flag_finite_math_only                               \
+   || !((MODE) == CCFPmode || (MODE) == CCFPEmode))
 
 #define REVERSE_CONDITION(CODE,MODE) \
   (((MODE) == CCFPmode || (MODE) == CCFPEmode) \

diff --git a/gcc/testsuite/gcc.target/arm/armv8_2-fp16-arith-1.c b/gcc/testsuite/gcc.target/arm/armv8_2-fp16-arith-1.c
index 52b87376dc782c9e6ef7e8427c782baa1813dc7f..f3fea524809e1dc856d029569b774fde2d7b81f7 100644 (file)
--- a/gcc/testsuite/gcc.target/arm/armv8_2-fp16-arith-1.c
+++ b/gcc/testsuite/gcc.target/arm/armv8_2-fp16-arith-1.c
@@ -106,8 +106,7 @@ TEST_CMP (greaterthanqual, >=, int16x8_t, float16x8_t)
 /* { dg-final { scan-assembler-times {vdiv\.f16\ts[0-9]+, s[0-9]+, s[0-9]+} 13 } }  */
 
 /* For float16_t.  */
-/* { dg-final { scan-assembler-times {vcmp\.f32\ts[0-9]+, s[0-9]+} 2 } }  */
-/* { dg-final { scan-assembler-times {vcmpe\.f32\ts[0-9]+, s[0-9]+} 4 } }  */
+/* { dg-final { scan-assembler-times {vcmp\.f32\ts[0-9]+, s[0-9]+} 6 } }  */
 
 /* For float16x4_t.  */
 /* { dg-final { scan-assembler-times {vceq\.f16\td[0-9]+, d[0-9]+} 2 } }  */