[llvm] 5c46c1c - Initialize output parameter

[Vitaly Buka via llvm-commits]

Author: Vitaly Buka
Date: 2022-01-07T15:21:22-08:00
New Revision: 5c46c1c23abb4a01f7f40bfcb8851cb893739e14

URL: https://github.com/llvm/llvm-project/commit/5c46c1c23abb4a01f7f40bfcb8851cb893739e14
DIFF: https://github.com/llvm/llvm-project/commit/5c46c1c23abb4a01f7f40bfcb8851cb893739e14.diff

LOG: Initialize output parameter

Or code like this have UB passing uninitialized CmpValue:

```
  int64_t CmpMask, CmpValue;
  if (!TII->analyzeCompare(MI, SrcReg, SrcReg2, CmpMask, CmpValue))
    return false;
  if (TII->optimizeCompareInstr(MI, SrcReg, SrcReg2, CmpMask, CmpValue, MRI)) {
```

Detected by msan with:
-Xclang -enable-noundef-analysis -mllvm -msan-eager-checks=1

Differential Revision: https://reviews.llvm.org/D116831

Added: 
    

Modified: 
    llvm/lib/Target/Hexagon/HexagonInstrInfo.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Target/Hexagon/HexagonInstrInfo.cpp b/llvm/lib/Target/Hexagon/HexagonInstrInfo.cpp
index dadedff4038e..9b4e92a16663 100644
--- a/llvm/lib/Target/Hexagon/HexagonInstrInfo.cpp
+++ b/llvm/lib/Target/Hexagon/HexagonInstrInfo.cpp
@@ -1893,6 +1893,7 @@ bool HexagonInstrInfo::analyzeCompare(const MachineInstr &MI, Register &SrcReg,
     case Hexagon::C4_cmplte:
     case Hexagon::C4_cmplteu:
       SrcReg2 = MI.getOperand(2).getReg();
+      Value = 0;
       return true;
 
     case Hexagon::C2_cmpeqi: