https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105776
Bug ID: 105776
Summary: Failure to recognize __builtin_mul_overflow pattern
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: gabravier at gmail dot com
Target Milestone: ---
int f4(unsigned x, unsigned y)
{
if (x == 0)
return 1;
return ((int)(x * y) / (int)x) == y;
}
can be optimized to
int f4(unsigned x, unsigned y)
{
int z;
return !__builtin_mul_overflow((int)x, (int)y, &z);
}
This transformation is done by LLVM, but not by GCC.
Note that this derivates from another function written as such:
int
f3 (unsigned x, unsigned y)
{
unsigned int r = x * y;
return !x || ((int) r / (int) x) == (int) y;
}
which does optimize correctly on x86 but not on aarch64 (where it generates
tree-optimized GIMPLE corresponding to the code above)
