[llvm] r362265 - [RegisterCoalescer] fix potential use of undef value. NFC

[Nick Desaulniers via llvm-commits]

Author: nickdesaulniers
Date: Fri May 31 14:20:13 2019
New Revision: 362265

URL: http://llvm.org/viewvc/llvm-project?rev=362265&view=rev
Log:
[RegisterCoalescer] fix potential use of undef value. NFC

Summary:
Fixes a warning produced from scan-build (llvm.org/reports/scan-build/),
further warnings found by annotation isMoveInstr [[nodiscard]].

isMoveInstr potentially does not assign to its parameters, so if they
were uninitialized, they will potentially stay uninitialized.  It seems
most call sites pass references to uninitialized values, then use them
without checking the return value.

Reviewers: wmi

Reviewed By: wmi

Subscribers: MatzeB, qcolombet, hiraditya, tpr, llvm-commits, srhines

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D62109

Modified:
    llvm/trunk/lib/CodeGen/RegisterCoalescer.cpp

Modified: llvm/trunk/lib/CodeGen/RegisterCoalescer.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/RegisterCoalescer.cpp?rev=362265&r1=362264&r2=362265&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/RegisterCoalescer.cpp (original)
+++ llvm/trunk/lib/CodeGen/RegisterCoalescer.cpp Fri May 31 14:20:13 2019
@@ -358,9 +358,10 @@ INITIALIZE_PASS_DEPENDENCY(AAResultsWrap
 INITIALIZE_PASS_END(RegisterCoalescer, "simple-register-coalescing",
                     "Simple Register Coalescing", false, false)
 
-static bool isMoveInstr(const TargetRegisterInfo &tri, const MachineInstr *MI,
-                        unsigned &Src, unsigned &Dst,
-                        unsigned &SrcSub, unsigned &DstSub) {
+LLVM_NODISCARD static bool isMoveInstr(const TargetRegisterInfo &tri,
+                                       const MachineInstr *MI, unsigned &Src,
+                                       unsigned &Dst, unsigned &SrcSub,
+                                       unsigned &DstSub) {
   if (MI->isCopy()) {
     Dst = MI->getOperand(0).getReg();
     DstSub = MI->getOperand(0).getSubReg();
@@ -1516,7 +1517,8 @@ MachineInstr *RegisterCoalescer::elimina
   // CoalescerPair may have a new register class with adjusted subreg indices
   // at this point.
   unsigned SrcReg, DstReg, SrcSubIdx, DstSubIdx;
-  isMoveInstr(*TRI, CopyMI, SrcReg, DstReg, SrcSubIdx, DstSubIdx);
+  if(!isMoveInstr(*TRI, CopyMI, SrcReg, DstReg, SrcSubIdx, DstSubIdx))
+    return nullptr;
 
   SlotIndex Idx = LIS->getInstructionIndex(*CopyMI);
   const LiveInterval &SrcLI = LIS->getInterval(SrcReg);
@@ -3514,7 +3516,8 @@ bool RegisterCoalescer::applyTerminalRul
   if (!UseTerminalRule)
     return false;
   unsigned DstReg, DstSubReg, SrcReg, SrcSubReg;
-  isMoveInstr(*TRI, &Copy, SrcReg, DstReg, SrcSubReg, DstSubReg);
+  if (!isMoveInstr(*TRI, &Copy, SrcReg, DstReg, SrcSubReg, DstSubReg))
+    return false;
   // Check if the destination of this copy has any other affinity.
   if (TargetRegisterInfo::isPhysicalRegister(DstReg) ||
       // If SrcReg is a physical register, the copy won't be coalesced.
@@ -3538,8 +3541,9 @@ bool RegisterCoalescer::applyTerminalRul
     if (&MI == &Copy || !MI.isCopyLike() || MI.getParent() != OrigBB)
       continue;
     unsigned OtherReg, OtherSubReg, OtherSrcReg, OtherSrcSubReg;
-    isMoveInstr(*TRI, &Copy, OtherSrcReg, OtherReg, OtherSrcSubReg,
-                OtherSubReg);
+    if (!isMoveInstr(*TRI, &Copy, OtherSrcReg, OtherReg, OtherSrcSubReg,
+                OtherSubReg))
+      return false;
     if (OtherReg == SrcReg)
       OtherReg = OtherSrcReg;
     // Check if OtherReg is a non-terminal.