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

[Craig Topper via llvm-commits]

The variable LatchBR is unused in Release builds and throws a warning.

~Craig

On Wed, May 3, 2017 at 10:44 AM, Anna Thomas via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

> 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
>
>
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