[X86AsmParser] Fix msan: use-of-uninitialized-value after r311639

[krasimir]

Summary

CodeGen/ms-inline-asm.c test triggers msan use-of-uninitialized-value here:
llvm/lib/MC/MCParser/AsmParser.cpp:5629:7

[coby]

@krasimir - was on the process of building the sanitizer and validating, you beat me to it

[coby]

include/llvm/MC/MCParser/MCTargetAsmParser.h

118

minor/style: consider the use of the first constructor (while passing AOK_IntelExpr & loc & len)

[krasimir]

include/llvm/MC/MCParser/MCTargetAsmParser.h

118

I don't understand? Are you talking delegating constructors?

[krasimir]

I'm gonna go ahead and commit this to unblock our integration. Will follow-up with style fixups.

[coby]

include/llvm/MC/MCParser/MCTargetAsmParser.h

118

indeed. i know it'll force the use of assignment for 'IntelExp', but I deem it as a fair tradeoff

[krasimir]

include/llvm/MC/MCParser/MCTargetAsmParser.h

118

IntelExpr has 5 fields. Plus the first constructor doesn't initialize IntelExp right now. Could you please send a snippet of how the constructors should be reorganized? My delegating constructors knowledge is a bit lacking.

[coby]

AsmRewrite(SMLoc loc, unsigned len, IntelExpr exp) : AsmRewrite(AOK_IntelExpr, loc, len) { IntelExp = exp; }

Same can be done for the 2nd c'tor (& 'label'). Again - it is a style thingy, nothing too cardinal, if you find the current implementation equivalent/better - keep it

[krasimir]

Thank you! I think your suggestion is nice. I'll create a follow-up patch for that!

[coby]

great :)
and thanks again for taking care of my code mischief

include/llvm/MC/MCParser/MCTargetAsmParser.h

struct AsmRewrite {
   IntelExpr IntelExp;
 
 public:
   AsmRewrite(AsmRewriteKind kind, SMLoc loc, unsigned len = 0, int64_t val = 0)
     : Kind(kind), Loc(loc), Len(len), Val(val) {}
   AsmRewrite(AsmRewriteKind kind, SMLoc loc, unsigned len, StringRef label)
     : Kind(kind), Loc(loc), Len(len), Val(0), Label(label) {}
   AsmRewrite(SMLoc loc, unsigned len, IntelExpr exp)
-    : Kind(AOK_IntelExpr), Loc(loc), Len(len), IntelExp(exp) {}
+    : Kind(AOK_IntelExpr), Loc(loc), Len(len), Val(0), IntelExp(exp) {}
 };
 
 struct ParseInstructionInfo {
   SmallVectorImpl<AsmRewrite> *AsmRewrites = nullptr;
 
   ParseInstructionInfo() = default;
   ParseInstructionInfo(SmallVectorImpl<AsmRewrite> *rewrites)
     : AsmRewrites(rewrites) {}