https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91191
Bug ID: 91191
Summary: vrp and boolean arguments
Product: gcc
Version: 9.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: wilson at gcc dot gnu.org
Target Milestone: ---
It appears that vrp isn't propagating the ranges of incoming boolean arguments.
Given this example:
unsigned char reg(_Bool b) {
union U {
unsigned char f0;
_Bool f1;
};
union U u;
u.f1 = b;
if (u.f0 > 1) {
// This cannot happen
// if b is only allowed
// to be 0 or 1:
return 42;
}
return 13;
}
clang optimizes this to unconditionally return 13, but gcc does a compare and
conditionally returns either 42 or 13 depending on the result of the compare.
This happens with both x86_64 and RISC-V.
Looking at the vrp dumps, I see
b_3(D): VARYING
