[PATCH] D51486: Add check to Latch's terminator in UnrollRuntimeLoopRemainder

[Rodrigo Caetano Rocha via Phabricator via llvm-commits]

rcorcs created this revision.
rcorcs added a reviewer: hfinkel.
Herald added subscribers: llvm-commits, dmgreen, zzheng.

In this patch, I'm adding an extra check to the Latch's terminator in llvm::UnrollRuntimeLoopRemainder,
similar to how it is already done in the llvm::UnrollLoop.

The compiler would crash if this function is called with a malformed loop.


Repository:
  rL LLVM

https://reviews.llvm.org/D51486

Files:
  lib/Transforms/Utils/LoopUnrollRuntime.cpp


Index: lib/Transforms/Utils/LoopUnrollRuntime.cpp
===================================================================
--- lib/Transforms/Utils/LoopUnrollRuntime.cpp
+++ lib/Transforms/Utils/LoopUnrollRuntime.cpp
@@ -545,6 +545,15 @@
   BasicBlock *Header = L->getHeader();
 
   BranchInst *LatchBR = cast<BranchInst>(Latch->getTerminator());
+
+  if (!LatchBR || LatchBR->isUnconditional()) {
+    // The loop-rotate pass can be helpful to avoid this in many cases.
+    LLVM_DEBUG(
+        dbgs()
+        << "Can't unroll; loop not terminated by a conditional branch.\n");
+    return false;
+  }
+
   unsigned ExitIndex = LatchBR->getSuccessor(0) == Header ? 1 : 0;
   BasicBlock *LatchExit = LatchBR->getSuccessor(ExitIndex);
   // Cloning the loop basic blocks (`CloneLoopBlocks`) requires that one of the


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