[PATCH] D67451: [AMDGPU] Fix crash in phi-elimination hook.

[Michael Liao via Phabricator via llvm-commits]

hliao created this revision.
hliao added reviewers: alex-t, rampitec, arsenm.
Herald added subscribers: llvm-commits, hiraditya, t-tye, tpr, dstuttard, nhaehnle, wdng, jvesely, kzhuravl.
Herald added a project: LLVM.

- Pre-check in case there's just a single PHI insn.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D67451

Files:
  llvm/lib/Target/AMDGPU/SIInstrInfo.cpp
  llvm/test/CodeGen/AMDGPU/phi-elimination-assertion.mir


Index: llvm/test/CodeGen/AMDGPU/phi-elimination-assertion.mir
===================================================================
--- llvm/test/CodeGen/AMDGPU/phi-elimination-assertion.mir
+++ llvm/test/CodeGen/AMDGPU/phi-elimination-assertion.mir
@@ -62,8 +62,32 @@
     S_NOP 0, implicit %4
 ...
 
+# The following test crashes in phi-elimination hooks.
+#
 # CHECK-LABEL: name:            bar
 # CHECK:   bb.3:
 # CHECK-NEXT:     dead %3:sreg_32_xm0 = IMPLICIT_DEF
 # CHECK-NEXT:     %2:sreg_32_xm0 = COPY killed %4
 # CHECK-NEXT:     S_NOP 0, implicit killed %2
+
+---
+name:            bax
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    S_CBRANCH_SCC0 %bb.2, implicit undef $scc
+
+  bb.1:
+    %1:sreg_32_xm0 = S_MOV_B32 255
+    S_BRANCH %bb.3
+
+  bb.2:
+    %2:sreg_32_xm0 = S_MOV_B32 254
+
+  bb.3:
+    %3:sreg_32_xm0 = PHI %2, %bb.2, %1, %bb.1
+...
+
+# CHECK-LABEL: name:            bax
+# CHECK:   bb.3:
+# CHECK-NEXT:     %2:sreg_32_xm0 = COPY killed %3
Index: llvm/lib/Target/AMDGPU/SIInstrInfo.cpp
===================================================================
--- llvm/lib/Target/AMDGPU/SIInstrInfo.cpp
+++ llvm/lib/Target/AMDGPU/SIInstrInfo.cpp
@@ -6415,11 +6415,13 @@
     MachineBasicBlock &MBB, MachineBasicBlock::iterator LastPHIIt,
     const DebugLoc &DL, Register Src, Register Dst) const {
   auto Cur = MBB.begin();
-  do {
+  while (Cur != MBB.end()) {
     if (!Cur->isPHI() && Cur->readsRegister(Dst))
       return BuildMI(MBB, Cur, DL, get(TargetOpcode::COPY), Dst).addReg(Src);
     ++Cur;
-  } while (Cur != MBB.end() && Cur != LastPHIIt);
+    if (Cur == LastPHIIt)
+      break;
+  }
 
   return TargetInstrInfo::createPHIDestinationCopy(MBB, LastPHIIt, DL, Src,
                                                    Dst);


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