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Diffstat (limited to 'llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp')
| -rw-r--r-- | llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp | 20 |
1 files changed, 20 insertions, 0 deletions
diff --git a/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp index d9489bc0a28..8d3f1f95f17 100644 --- a/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp +++ b/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp @@ -2069,10 +2069,30 @@ void LSRInstance::OptimizeLoopTermCond() { SmallPtrSet<Instruction *, 4> PostIncs; + // We need a different set of heuristics for rotated and non-rotated loops. + // If a loop is rotated then the latch is also the backedge, so inserting + // post-inc expressions just before the latch is ideal. To reduce live ranges + // it also makes sense to rewrite terminating conditions to use post-inc + // expressions. + // + // If the loop is not rotated then the latch is not a backedge; the latch + // check is done in the loop head. Adding post-inc expressions before the + // latch will cause overlapping live-ranges of pre-inc and post-inc expressions + // in the loop body. In this case we do *not* want to use post-inc expressions + // in the latch check, and we want to insert post-inc expressions before + // the backedge. BasicBlock *LatchBlock = L->getLoopLatch(); SmallVector<BasicBlock*, 8> ExitingBlocks; L->getExitingBlocks(ExitingBlocks); + if (llvm::all_of(ExitingBlocks, [&LatchBlock](const BasicBlock *BB) { + return LatchBlock != BB; + })) { + // The backedge doesn't exit the loop; treat this as a head-tested loop. + IVIncInsertPos = LatchBlock->getTerminator(); + return; + } + // Otherwise treat this as a rotated loop. for (BasicBlock *ExitingBlock : ExitingBlocks) { // Get the terminating condition for the loop if possible. If we |
