https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86628
Bug ID: 86628
Summary: Missed simplification of division
Product: gcc
Version: tree-ssa
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: david.bolvansky at gmail dot com
Target Milestone: ---
Hello,
for code:
int f(int x, int y, int z) {
return (x * y * z) / (y * z);
}
GCC 8.1 (x86-64) with -O3 emits:
f(int, int, int):
mov eax, edi
imul eax, esi
imul esi, edx
imul eax, edx
cdq
idiv esi
ret
but one multiplication can be removed, as Clang does it:
f(int, int, int):
imul esi, edx
imul edi, esi
mov eax, edi
cdq
idiv esi
ret
Also, for:
unsigned f2(unsigned x, unsigned y, unsigned z) {
return (x*z) / (y*z);
}
f2(unsigned int, unsigned int, unsigned int):
mov eax, edi
imul esi, edx
imul eax, edx
xor edx, edx
div esi
ret
This could be simplified to "x/y". For a signed case it could be possible too,
just z = -1 needs to be checked.
