https://bugs.llvm.org/show_bug.cgi?id=34920
Bug ID: 34920
Summary: __builtin_mul_overflow not lowered correctly
Product: clang
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: normal
Priority: P
Component: LLVM Codegen
Assignee: unassignedclangb...@nondot.org
Reporter: v...@apple.com
CC: llvm-bugs@lists.llvm.org
Created attachment 19264
--> https://bugs.llvm.org/attachment.cgi?id=19264&action=edit
Miscompilation example
We're miscompiling calls to __builtin_mul_overflow(), specifically when both
arguments have the same width but differ in signed-ness:
https://godbolt.org/g/cfmEEf (I've also attached the example file).
W're emitting calls to overflow intrinsics which return i33, i65, and i129.
These are lowered into runtime calls which aren't correct: for example,
___mulodi4 doesn't correctly report overflow for 33-bit arguments.
Should we require that arguments to the overflow intrinsics have the same
signed-ness if they have the same width? Or should we provide backend and
runtime support for these exotic overflow checks?
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