diff options
| -rw-r--r-- | lib/Transforms/Scalar/LoopRotation.cpp | 20 | ||||
| -rw-r--r-- | test/Transforms/LoopRotate/phi-duplicate.ll | 22 |
2 files changed, 37 insertions, 5 deletions
diff --git a/lib/Transforms/Scalar/LoopRotation.cpp b/lib/Transforms/Scalar/LoopRotation.cpp index 1e4bfa94be..31957ddac1 100644 --- a/lib/Transforms/Scalar/LoopRotation.cpp +++ b/lib/Transforms/Scalar/LoopRotation.cpp @@ -261,6 +261,26 @@ bool LoopRotate::rotateLoop(Loop *Lp, LPPassManager &LPM) { // NewHeader is now the header of the loop. L->moveToHeader(NewHeader); + // Move the original header to the bottom of the loop, where it now more + // naturally belongs. This isn't necessary for correctness, and CodeGen can + // usually reorder blocks on its own to fix things like this up, but it's + // still nice to keep the IR readable. + // + // The original header should have only one predecessor at this point, since + // we checked that the loop had a proper preheader and unique backedge before + // we started. + assert(OrigHeader->getSinglePredecessor() && + "Original loop header has too many predecessors after loop rotation!"); + OrigHeader->moveAfter(OrigHeader->getSinglePredecessor()); + + // Also, since this original header only has one predecessor, zap its + // PHI nodes, which are now trivial. + FoldSingleEntryPHINodes(OrigHeader); + + // TODO: We could just go ahead and merge OrigHeader into its predecessor + // at this point, if we don't mind updating dominator info. + + // Establish a new preheader, update dominators, etc. preserveCanonicalLoopForm(LPM); ++NumRotated; diff --git a/test/Transforms/LoopRotate/phi-duplicate.ll b/test/Transforms/LoopRotate/phi-duplicate.ll index 9a64e2a9a8..5403e723ee 100644 --- a/test/Transforms/LoopRotate/phi-duplicate.ll +++ b/test/Transforms/LoopRotate/phi-duplicate.ll @@ -27,9 +27,21 @@ for.body: ; preds = %for.cond for.end: ; preds = %for.cond ret void } -; Should only end up with one phi. -; CHECK: for.body: -; CHECK-NEXT: %j.02 = phi i64 -; CHECK-NOT: phi -; CHECK: ret void +; Should only end up with one phi. Also, the original for.cond block should +; be moved to the end of the loop so that the new loop header pleasantly +; ends up at the top. + +; CHECK: define void @test +; CHECK-NEXT: entry: +; CHECK-NEXT: icmp slt i64 +; CHECK-NEXT: br i1 +; CHECK-NOT: : +; CHECK: bb.nph: +; CHECK-NEXT: br label %for.body +; CHECK-NOT: : +; CHECK: for.body: +; CHECK-NEXT: %j.02 = phi i64 +; CHECK-NOT: phi +; CHECK: ret void +; CHECK-NEXT: } |