[llvm] r302058 - [RuntimeLoopUnroller] Add assert that we dont unroll non-rotated loops

[Anna Thomas via llvm-commits]

Author: annat
Date: Wed May  3 12:43:59 2017
New Revision: 302058

URL: http://llvm.org/viewvc/llvm-project?rev=302058&view=rev
Log:
[RuntimeLoopUnroller] Add assert that we dont unroll non-rotated loops

Summary:
Cloning basic blocks in the loop for runtime loop unroller depends on loop being
in rotated form (i.e. loop latch target is the exit block).
Assert that this is true, so that callers of runtime loop unroller pass in
canonical loops.
The single caller of this function has that check recently added:
https://reviews.llvm.org/rL301239

Reviewers: davide

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D32801

Modified:
    llvm/trunk/lib/Transforms/Utils/LoopUnrollRuntime.cpp

Modified: llvm/trunk/lib/Transforms/Utils/LoopUnrollRuntime.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/LoopUnrollRuntime.cpp?rev=302058&r1=302057&r2=302058&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/LoopUnrollRuntime.cpp (original)
+++ llvm/trunk/lib/Transforms/Utils/LoopUnrollRuntime.cpp Wed May  3 12:43:59 2017
@@ -512,6 +512,13 @@ bool llvm::UnrollRuntimeLoopRemainder(Lo
 
   BasicBlock *Latch = L->getLoopLatch();
 
+  // Cloning the loop basic blocks (`CloneLoopBlocks`) requires that one of the
+  // targets of the Latch be the single exit block out of the loop. This needs
+  // to be guaranteed by the callers of UnrollRuntimeLoopRemainder.
+  BranchInst *LatchBR = cast<BranchInst>(Latch->getTerminator());
+  assert(LatchBR->getSuccessor(0) == Exit ||
+         LatchBR->getSuccessor(1) == Exit && "loop latch successor should be "
+                                             "exit block!");
   // Loop structure is the following:
   //
   // PreHeader