https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89518
Bug ID: 89518
Summary: missed optimisation for array address calculations
Product: gcc
Version: 8.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: arnaud02 at users dot sourceforge.net
Target Milestone: ---
Considering:
int f(int index, int stride) {
const int i1 = index / stride;
const int i2 = index % stride;
const int index2 = i1*stride+i2;
return index2; // expect: index2 = index
}
gcc 8.3 with "-O3" on x84_64 emits:
f(int, int):
mov eax, edi
cdq
idiv esi
imul eax, esi
add eax, edx
ret
By contrast, clang 7 with "-O3" emits
f(int, int):
mov eax, edi
ret
MSVC 2017 with "/O2" emits:
int f(int,int)
mov eax, ecx
ret 0
Is there a way to persuade gcc to simplify this expression at compile time?
