https://bugs.llvm.org/show_bug.cgi?id=36886
Bug ID: 36886
Summary: bool parameter is tested as a 32-bit value, should use
only the low byte
Product: new-bugs
Version: unspecified
Hardware: PC
OS: Windows NT
Status: NEW
Severity: enhancement
Priority: P
Component: new bugs
Assignee: unassignedb...@nondot.org
Reporter: dma...@mozilla.com
CC: llvm-bugs@lists.llvm.org
__declspec(noinline) int fn(bool b) { return b ? 0x42 : 0; }
At -O1 and higher on 64-bit Windows, clang-cl generates code that goes like:
test!fn:
00000001`40001000 85c9 test ecx,ecx
00000001`40001002 b842000000 mov eax,42h
00000001`40001007 0f44c1 cmove eax,ecx
00000001`4000100a c3 ret
where the function tests the full 32-bit value of ecx. This can end up taking
the wrong code path if the caller only filled in the low byte of the register
and the upper bytes are garbage. (For what it's worth, MSVC looks at only the
low byte in this case.)
clang version 7.0.0 (trunk 328367)
Reduced from
https://searchfox.org/mozilla-central/rev/de5c4376b89c3603341d226a65acea12f8851ec5/netwerk/base/nsUDPSocket.cpp#571
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