https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92229
Bug ID: 92229
Summary: Optimization makes it impossible to read overflow flag
Product: gcc
Version: 10.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: arieltorti14 at gmail dot com
Target Milestone: ---
I'm implementing a builtin to read the overflow flag. It is meant to be used to
simply the overflow checking code, instead of doing:
ov = __builtin_smul_overflow(a, b, &res);
if (ov) { ... }
One could make the code more readable by using:
res = a * b;
if (__builtin_overflow_p()) { ... }
The problem GCC optimizes many multiplication and addition operations by using
`lea` which doesn't set the overflow flag, which makes it impossible to do the
check.
What approach could I take to implement this ? Do note that this builtin is
only available on x86.
