[PATCH] D112980: [LoopInfo] Fix a bug in the function getInductionVariable

[duanbo via Phabricator via llvm-commits]

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There is a bug in getInductionVariable. From code, the way this function gets the induction variable is by judging whether StepInst or IndVar in the phi statement is one of the operands of CMP. It will perform dyn_cast operations. But if the LatchCmpOp0/LatchCmpOp1 is a constant, it will be cast to null. The same situation exists when getting the Stepinst, the subsequent comparison may result in null == null, which is meaningless. The induction variable will be the first phi of the loop, and this does not match the logic of this function.


https://reviews.llvm.org/D112980

Files:
  llvm/lib/Analysis/LoopInfo.cpp


Index: llvm/lib/Analysis/LoopInfo.cpp
===================================================================
--- llvm/lib/Analysis/LoopInfo.cpp
+++ llvm/lib/Analysis/LoopInfo.cpp
@@ -301,15 +301,16 @@
   if (!CmpInst)
     return nullptr;
 
-  Instruction *LatchCmpOp0 = dyn_cast<Instruction>(CmpInst->getOperand(0));
-  Instruction *LatchCmpOp1 = dyn_cast<Instruction>(CmpInst->getOperand(1));
+  Value *LatchCmpOp0 = CmpInst->getOperand(0);
+  Value *LatchCmpOp0 = CmpInst->getOperand(1);
 
   for (PHINode &IndVar : Header->phis()) {
     InductionDescriptor IndDesc;
     if (!InductionDescriptor::isInductionPHI(&IndVar, this, &SE, IndDesc))
       continue;
 
-    Instruction *StepInst = IndDesc.getInductionBinOp();
+    BasicBlock *Latch = this->getLoopLatch();
+    Value *StepInst = IndVar.getIncomingValueForBlock(Latch);
 
     // case 1:
     // IndVar = phi[{InitialValue, preheader}, {StepInst, latch}]


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