https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67929
Bug ID: 67929
Summary: [4.9/5/6 Regression][arm] Wrong code for FP
mult-by-power-of-2 + int conversion
Product: gcc
Version: 6.0
Status: UNCONFIRMED
Keywords: wrong-code
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: ktkachov at gcc dot gnu.org
Target Milestone: ---
Target: arm*
Testcase:
int
foo (float a)
{
return a * 4.9f;
}
int
main (void)
{
if (foo (10.0f) != 49)
__builtin_abort ();
return 0;
}
Compiled with -Ofast -mfpu=vfpv3 -mfloat-abi=hard -mcpu=cortex-a15 -fno-inline
aborts.
The problem is foo (10.0f) returns 40.
This is because the combine_vcvtf2i triggers where its predicate should have
rejected 4.9f
The vfp3_const_double_for_bits function in arm.c is too liberal and accepts any
FP constant that, when truncated, evaluates to a power of 2 FP constant.
