-O1 produces binary that valgrind complains about

[llvmbot]

Bugzilla Link	10226
Resolution	FIXED
Resolved on	Jan 19, 2020 23:26
Version	trunk
OS	All
Attachments	run.sh, test.bc, test2-0.s, test2-1.s, syms
Reporter	LLVM Bugzilla Contributor
CC	@asl,@MaskRay

Extended Description

I noticed that valgrind would complain about a clang compiled clang, but not a gcc compiled clang. I reduced it to _ZNK5clang4Expr21refersToVectorElementEv being "miscompiled" (at least producing code that valgrind doesn't like.

[llvmbot]

This might be Valgrind bug 242137. I would have fixed it
bug I didn't get much feedback on it. In particular, try
the fix at http://bugs.kde.org/show_bug.cgi?id=242137#c3
I would be interested to know if that helps.

[llvmbot]

Unfortunately that was not it. The error valgrind prints is

==8292== Conditional jump or move depends on uninitialised value(s)
==8292== at 0x408075: clang::Expr::refersToVectorElement() const (in /home/espindola/llvm/t/clang-test-1)
==8292== by 0x11A3EAA: clang::InitializationSequence::InitializationSequence(clang::Sema&, clang::InitializedEntity const&, clang::InitializationKind const&, clang::Expr**, unsigned int) (in /home/espindola/llvm/t/clang-test-1)

The code area looks like

408061: 81 fa 00 80 02 00 cmp $0x28000,%edx
408067: 89 7c 24 34 mov %edi,0x34(%rsp)
40806b: 48 89 44 24 28 mov %rax,0x28(%rsp)
408070: 40 88 74 24 27 mov %sil,0x27(%rsp)
408075: 75 54 jne 4080cb <_ZNK5clang4Expr21refersToVectorElementEv+0xab>
408077: eb 00 jmp 408079 <_ZNK5clang4Expr21refersToVectorElementEv+0x59>
408079: 8a 44 24 27 mov 0x27(%rsp),%al
40807d: 3c 01 cmp $0x1,%al
40807f: 75 4a jne 4080cb <_ZNK5clang4Expr21refersToVectorElementEv+0xab>
408081: eb 00 jmp 408083 <_ZNK5clang4Expr21refersToVectorElementEv+0x63>

The full testcase is at
http://people.mozilla.org/~respindola/llvm-or-valgrind-bug.tar.bz2

[MaskRay]

valgrind --tool=memcheck --leak-check=yes ~/llvm/Debug/bin/clang -c a.c

works fine