[LoopSimplify] Rebuild LCSSA for the inner loop after separating nested loops.
Summary:
This hopefully fixes PR28825. The problem now was that a value from the
original loop was used in a subloop, which became a sibling after separation.
While a subloop doesn't need an lcssa phi node, a sibling does, and that's
where we broke LCSSA. The most natural way to fix this now is to simply call
formLCSSA on the original loop: it'll do what we've been doing before plus
it'll cover situations described above.
I think we don't need to run formLCSSARecursively here, and we have an assert
to verify this (I've tried testing it on LLVM testsuite + SPECs). I'd be happy
to be corrected here though.
I also changed a run line in the test from '-lcssa -loop-unroll' to
'-lcssa -loop-simplify -indvars', because it exercises LCSSA
preservation to the same extent, but also makes less unrelated
transformation on the CFG, which makes it easier to verify.
Reviewers: chandlerc, sanjoy, silvas
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D23288
llvm-svn: 278173
diff --git a/llvm/lib/Transforms/Utils/LoopSimplify.cpp b/llvm/lib/Transforms/Utils/LoopSimplify.cpp
index d2ccb16..26b59ad 100644
--- a/llvm/lib/Transforms/Utils/LoopSimplify.cpp
+++ b/llvm/lib/Transforms/Utils/LoopSimplify.cpp
@@ -361,39 +361,11 @@
// Fix LCSSA form for L. Some values, which previously were only used inside
// L, can now be used in NewOuter loop. We need to insert phi-nodes for them
// in corresponding exit blocks.
+ // We don't need to form LCSSA recursively, because there cannot be uses
+ // inside a newly created loop of defs from inner loops as those would
+ // already be a use of an LCSSA phi node.
+ formLCSSA(*L, *DT, LI, SE);
- // Go through all instructions in OuterLoopBlocks and check if they are
- // using operands from the inner loop. In this case we'll need to fix LCSSA
- // for these instructions.
- SmallSetVector<Instruction *, 8> WorklistSet;
- for (BasicBlock *OuterBB: OuterLoopBlocks) {
- for (Instruction &I : *OuterBB) {
- for (Value *Op : I.operands()) {
- Instruction *OpI = dyn_cast<Instruction>(Op);
- if (!OpI || !L->contains(OpI))
- continue;
- WorklistSet.insert(OpI);
- }
- }
- }
- // We also need to check exit blocks of the outer loop - it might be using
- // values from what now became an inner loop.
- SmallVector<BasicBlock*, 8> ExitBlocks;
- NewOuter->getExitBlocks(ExitBlocks);
- for (BasicBlock *ExitBB: ExitBlocks) {
- for (Instruction &I : *ExitBB) {
- for (Value *Op : I.operands()) {
- Instruction *OpI = dyn_cast<Instruction>(Op);
- if (!OpI || !L->contains(OpI))
- continue;
- WorklistSet.insert(OpI);
- }
- }
- }
-
- SmallVector<Instruction *, 8> Worklist(WorklistSet.begin(),
- WorklistSet.end());
- formLCSSAForInstructions(Worklist, *DT, *LI);
assert(NewOuter->isRecursivelyLCSSAForm(*DT) &&
"LCSSA is broken after separating nested loops!");
}