[PATCH] D25963: [LoopUnroll] Implement profile-based loop peeling

[Adam Nemet via Phabricator via llvm-commits]

anemet accepted this revision.
anemet added a comment.

LGTM with some minor changes.



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Comment at: lib/Transforms/Utils/LoopUnrollPeel.cpp:137
+    uint64_t FallThruWeight =
+        PeeledHeaderWeight * ((float)(AvgIters - IterNumber) / AvgIters * 0.9);
+    uint64_t ExitWeight = PeeledHeaderWeight - FallThruWeight;
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Why the 0.9?  This also needs a comment.


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Comment at: lib/Transforms/Utils/LoopUnrollPeel.cpp:204-219
+  // Change the incoming values to the ones defined in the preheader or
+  // the previous cloned loop body.
+  for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
+    PHINode *NewPHI = cast<PHINode>(VMap[&*I]);
+    if (IterNumber == 0) {
+      VMap[&*I] = NewPHI->getIncomingValueForBlock(PreHeader);
+    } else {
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This needs a bit more comment; here we're turning values that were before defined by the loop PHIs to use values directly from the preheader or the previous cloned loop body.


https://reviews.llvm.org/D25963