https://bugs.llvm.org/show_bug.cgi?id=38665
Bug ID: 38665
Summary: __builtin_mul_overflow with mixed sign gives different
results compared to GCC
Product: clang
Version: 7.0
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: LLVM Codegen
Assignee: unassignedclangb...@nondot.org
Reporter: jo...@netbsd.org
CC: llvm-bugs@lists.llvm.org
Try to build:
#include <stddef.h>
int f(size_t a, size_t b) {
ptrdiff_t x;
return __builtin_mul_overflow(a, b, &x);
}
with clang and gcc for x86_64.
(1) GCC seems to interpret this as uint64_t x uint64_t -> uint64_t
multiplication
(2) Clang seems to widen the types and goes for int128_t instead (__muloti4).
This difference in interpretation seems to break the memory overflow checks in
GNU m4.
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