https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109829
Bug ID: 109829
Summary: Optimizing __builtin_signbit(x) ? -x : x or abs for FP
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: antoshkka at gmail dot com
Target Milestone: ---
Consider the following 2 functions:
__float128 abs1(__float128 x) { return __builtin_fabsf128(x); }
__float128 abs2(__float128 x) { return __builtin_signbit(x) ? -x : x; }
They should provide the same results, however the codegen is different:
abs1(__float128):
pand xmm0, XMMWORD PTR .LC0[rip]
ret
abs2(__float128):
movmskps eax, xmm0
test al, 8
je .L4
pxor xmm0, XMMWORD PTR .LC1[rip]
.L4:
ret
Looks like match.pd miss the __builtin_signbit(x) ? -x : x ->
__builtin_fabs*(x) pattern.
Playground: https://godbolt.org/z/bsxeozGqv
