[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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@362265 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/RegisterCoalescer.cpp b/lib/CodeGen/RegisterCoalescer.cpp
index 58e29d613f0e94aebc304d03ef9775566bb5ad7f..1f0046ab164e3e315c47fea521a6369825e4394f 100644 (file)
--- a/lib/CodeGen/RegisterCoalescer.cpp
+++ b/lib/CodeGen/RegisterCoalescer.cpp
@@ -358,9 +358,10 @@ INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
 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::eliminateUndefCopy(MachineInstr *CopyMI) {
   // 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::applyTerminalRule(const MachineInstr &Copy) const {
   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::applyTerminalRule(const MachineInstr &Copy) const {
     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.