diff options
Diffstat (limited to 'lib/Transforms/Utils/BreakCriticalEdges.cpp')
-rw-r--r-- | lib/Transforms/Utils/BreakCriticalEdges.cpp | 76 |
1 files changed, 30 insertions, 46 deletions
diff --git a/lib/Transforms/Utils/BreakCriticalEdges.cpp b/lib/Transforms/Utils/BreakCriticalEdges.cpp index 080363db7b..0939252f5c 100644 --- a/lib/Transforms/Utils/BreakCriticalEdges.cpp +++ b/lib/Transforms/Utils/BreakCriticalEdges.cpp @@ -299,9 +299,8 @@ BasicBlock *llvm::SplitCriticalEdge(TerminatorInst *TI, unsigned SuccNum, P->addBasicBlockToLoop(NewBB, LI->getBase()); } } - // If TIBB is in a loop and DestBB is outside of that loop, split the - // other exit blocks of the loop that also have predecessors outside - // the loop, to maintain a LoopSimplify guarantee. + // If TIBB is in a loop and DestBB is outside of that loop, we may need + // to update LoopSimplify form and LCSSA form. if (!TIL->contains(DestBB) && P->mustPreserveAnalysisID(LoopSimplifyID)) { assert(!TIL->contains(NewBB) && @@ -311,50 +310,35 @@ BasicBlock *llvm::SplitCriticalEdge(TerminatorInst *TI, unsigned SuccNum, if (P->mustPreserveAnalysisID(LCSSAID)) createPHIsForSplitLoopExit(TIBB, NewBB, DestBB); - // For each unique exit block... - // FIXME: This code is functionally equivalent to the corresponding - // loop in LoopSimplify. - SmallVector<BasicBlock *, 4> ExitBlocks; - TIL->getExitBlocks(ExitBlocks); - for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) { - // Collect all the preds that are inside the loop, and note - // whether there are any preds outside the loop. - SmallVector<BasicBlock *, 4> Preds; - bool HasPredOutsideOfLoop = false; - BasicBlock *Exit = ExitBlocks[i]; - for (pred_iterator I = pred_begin(Exit), E = pred_end(Exit); - I != E; ++I) { - BasicBlock *P = *I; - if (TIL->contains(P)) { - if (isa<IndirectBrInst>(P->getTerminator())) { - Preds.clear(); - break; - } - Preds.push_back(P); - } else { - HasPredOutsideOfLoop = true; - } - } - // If there are any preds not in the loop, we'll need to split - // the edges. The Preds.empty() check is needed because a block - // may appear multiple times in the list. We can't use - // getUniqueExitBlocks above because that depends on LoopSimplify - // form, which we're in the process of restoring! - if (!Preds.empty() && HasPredOutsideOfLoop) { - if (!Exit->isLandingPad()) { - BasicBlock *NewExitBB = - SplitBlockPredecessors(Exit, Preds, "split", P); - if (P->mustPreserveAnalysisID(LCSSAID)) - createPHIsForSplitLoopExit(Preds, NewExitBB, Exit); - } else if (SplitLandingPads) { - SmallVector<BasicBlock*, 8> NewBBs; - SplitLandingPadPredecessors(Exit, Preds, - ".split1", ".split2", - P, NewBBs); - if (P->mustPreserveAnalysisID(LCSSAID)) - createPHIsForSplitLoopExit(Preds, NewBBs[0], Exit); - } + // The only that we can break LoopSimplify form by splitting a critical + // edge is if after the split there exists some edge from TIL to DestBB + // *and* the only edge into DestBB from outside of TIL is that of + // NewBB. If the first isn't true, then LoopSimplify still holds, NewBB + // is the new exit block and it has no non-loop predecessors. If the + // second isn't true, then DestBB was not in LoopSimplify form prior to + // the split as it had a non-loop predecessor. In both of these cases, + // the predecessor must be directly in TIL, not in a subloop, or again + // LoopSimplify doesn't hold. + SmallVector<BasicBlock *, 4> LoopPreds; + for (pred_iterator I = pred_begin(DestBB), E = pred_end(DestBB); I != E; + ++I) { + BasicBlock *P = *I; + if (P == NewBB) + continue; // The new block is known. + if (LI->getLoopFor(P) != TIL) { + // No need to re-simplify, it wasn't to start with. + LoopPreds.clear(); + break; } + LoopPreds.push_back(P); + } + if (!LoopPreds.empty()) { + assert(!DestBB->isLandingPad() && + "We don't split edges to landing pads!"); + BasicBlock *NewExitBB = + SplitBlockPredecessors(DestBB, LoopPreds, "split", P); + if (P->mustPreserveAnalysisID(LCSSAID)) + createPHIsForSplitLoopExit(LoopPreds, NewExitBB, DestBB); } } // LCSSA form was updated above for the case where LoopSimplify is |