[llvm] r275891 - [LoopSimplify] Update LCSSA after separating nested loops.
Michael Zolotukhin via llvm-commits
llvm-commits at lists.llvm.org
Mon Jul 18 12:44:20 PDT 2016
Author: mzolotukhin
Date: Mon Jul 18 14:44:19 2016
New Revision: 275891
URL: http://llvm.org/viewvc/llvm-project?rev=275891&view=rev
Log:
[LoopSimplify] Update LCSSA after separating nested loops.
Summary:
Usually LCSSA survives this transformation, but in some cases (see
attached test) it doesn't: values from the original loop after
separating might be used from the outer loop. Before the transformation
it was the same loop, so LCSSA phis were not required.
This fixes PR28272.
Reviewers: sanjoy, hfinkel, chandlerc
Subscribers: llvm-commits
Differential Revision: http://reviews.llvm.org/D21665
Added:
llvm/trunk/test/Transforms/LoopSimplify/pr28272.ll
Modified:
llvm/trunk/lib/Transforms/Utils/LoopSimplify.cpp
Modified: llvm/trunk/lib/Transforms/Utils/LoopSimplify.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/LoopSimplify.cpp?rev=275891&r1=275890&r2=275891&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/LoopSimplify.cpp (original)
+++ llvm/trunk/lib/Transforms/Utils/LoopSimplify.cpp Mon Jul 18 14:44:19 2016
@@ -327,6 +327,8 @@ static Loop *separateNestedLoop(Loop *L,
else
NewOuter->addChildLoop(L->removeChildLoop(SubLoops.begin() + I));
+ SmallVector<BasicBlock *, 8> OuterLoopBlocks;
+ OuterLoopBlocks.push_back(NewBB);
// Now that we know which blocks are in L and which need to be moved to
// OuterLoop, move any blocks that need it.
for (unsigned i = 0; i != L->getBlocks().size(); ++i) {
@@ -334,12 +336,53 @@ static Loop *separateNestedLoop(Loop *L,
if (!BlocksInL.count(BB)) {
// Move this block to the parent, updating the exit blocks sets
L->removeBlockFromLoop(BB);
- if ((*LI)[BB] == L)
+ if ((*LI)[BB] == L) {
LI->changeLoopFor(BB, NewOuter);
+ OuterLoopBlocks.push_back(BB);
+ }
--i;
}
}
+ // Split edges to exit blocks from the inner loop, if they emerged in the
+ // process of separating the outer one.
+ SmallVector<BasicBlock *, 8> ExitBlocks;
+ L->getExitBlocks(ExitBlocks);
+ SmallSetVector<BasicBlock *, 8> ExitBlockSet(ExitBlocks.begin(),
+ ExitBlocks.end());
+ for (BasicBlock *ExitBlock : ExitBlockSet) {
+ if (any_of(predecessors(ExitBlock),
+ [L](BasicBlock *BB) { return !L->contains(BB); })) {
+ rewriteLoopExitBlock(L, ExitBlock, DT, LI, PreserveLCSSA);
+ }
+ }
+
+ if (PreserveLCSSA) {
+ // 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.
+
+ // 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);
+ }
+ }
+ }
+ SmallVector<Instruction *, 8> Worklist(WorklistSet.begin(),
+ WorklistSet.end());
+ formLCSSAForInstructions(Worklist, *DT, *LI);
+ assert(NewOuter->isRecursivelyLCSSAForm(*DT) &&
+ "LCSSA is broken after separating nested loops!");
+ }
+
return NewOuter;
}
@@ -541,17 +584,12 @@ ReprocessLoop:
SmallSetVector<BasicBlock *, 8> ExitBlockSet(ExitBlocks.begin(),
ExitBlocks.end());
for (BasicBlock *ExitBlock : ExitBlockSet) {
- for (pred_iterator PI = pred_begin(ExitBlock), PE = pred_end(ExitBlock);
- PI != PE; ++PI)
- // Must be exactly this loop: no subloops, parent loops, or non-loop preds
- // allowed.
- if (!L->contains(*PI)) {
- if (rewriteLoopExitBlock(L, ExitBlock, DT, LI, PreserveLCSSA)) {
- ++NumInserted;
- Changed = true;
- }
- break;
- }
+ if (any_of(predecessors(ExitBlock),
+ [L](BasicBlock *BB) { return !L->contains(BB); })) {
+ rewriteLoopExitBlock(L, ExitBlock, DT, LI, PreserveLCSSA);
+ ++NumInserted;
+ Changed = true;
+ }
}
// If the header has more than two predecessors at this point (from the
Added: llvm/trunk/test/Transforms/LoopSimplify/pr28272.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopSimplify/pr28272.ll?rev=275891&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/LoopSimplify/pr28272.ll (added)
+++ llvm/trunk/test/Transforms/LoopSimplify/pr28272.ll Mon Jul 18 14:44:19 2016
@@ -0,0 +1,76 @@
+; RUN: opt < %s -lcssa -loop-unroll -S | FileCheck %s
+target triple = "x86_64-unknown-linux-gnu"
+
+; PR28272
+; When LoopSimplify separates nested loops, it might break LCSSA form: values
+; from the original loop might be used in the outer loop. This test invokes
+; loop-unroll, which calls loop-simplify before itself. If LCSSA is broken
+; after loop-simplify, we crash on assertion.
+
+; CHECK-LABEL: @foo
+define void @foo() {
+entry:
+ br label %header
+
+header:
+ br label %loop1
+
+loop1:
+ br i1 true, label %loop1, label %bb43
+
+bb43:
+ %a = phi i32 [ undef, %loop1 ], [ 0, %bb45 ], [ %a, %bb54 ]
+ %b = phi i32 [ 0, %loop1 ], [ 1, %bb54 ], [ %c, %bb45 ]
+ br i1 true, label %bb114, label %header
+
+bb114:
+ %c = add i32 0, 1
+ %d = add i32 0, 1
+ br i1 true, label %bb45, label %bb54
+
+bb45:
+ %x = add i32 %d, 0
+ br label %bb43
+
+bb54:
+ br label %bb43
+}
+
+; CHECK-LABEL: @foo2
+define void @foo2() {
+entry:
+ br label %outer
+
+outer.loopexit:
+ br label %outer
+
+outer:
+ br label %loop1
+
+loop1:
+ br i1 true, label %loop1, label %loop2.preheader
+
+loop2.preheader:
+ %a.ph = phi i32 [ undef, %loop1 ]
+ %b.ph = phi i32 [ 0, %loop1 ]
+ br label %loop2
+
+loop2:
+ %a = phi i32 [ 0, %loop2.if.true ], [ %a, %loop2.if.false ], [ %a.ph, %loop2.preheader ], [0, %bb]
+ %b = phi i32 [ 1, %loop2.if.false ], [ %c, %loop2.if.true ], [ %b.ph, %loop2.preheader ], [%c, %bb]
+ br i1 true, label %loop2.if, label %outer.loopexit
+
+loop2.if:
+ %c = add i32 0, 1
+ switch i32 undef, label %loop2.if.false [i32 0, label %loop2.if.true
+ i32 1, label %bb]
+
+loop2.if.true:
+ br i1 undef, label %loop2, label %bb
+
+loop2.if.false:
+ br label %loop2
+
+bb:
+ br label %loop2
+}
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