diff options
Diffstat (limited to 'llvm/lib/Transforms')
| -rw-r--r-- | llvm/lib/Transforms/Utils/MemorySSA.cpp | 20 |
1 files changed, 16 insertions, 4 deletions
diff --git a/llvm/lib/Transforms/Utils/MemorySSA.cpp b/llvm/lib/Transforms/Utils/MemorySSA.cpp index 8455f79b811..234d1af569c 100644 --- a/llvm/lib/Transforms/Utils/MemorySSA.cpp +++ b/llvm/lib/Transforms/Utils/MemorySSA.cpp @@ -1288,6 +1288,7 @@ private: // Note: Correctness depends on this being initialized to 0, which densemap // does unsigned long LowerBound; + const BasicBlock *LowerBoundBlock; // This is where the last walk for this memory location ended. unsigned long LastKill; bool LastKillValid; @@ -1333,7 +1334,6 @@ void MemorySSA::OptimizeUses::optimizeUsesInBlock( VersionStack.pop_back(); ++PopEpoch; } - for (MemoryAccess &MA : *Accesses) { auto *MU = dyn_cast<MemoryUse>(&MA); if (!MU) { @@ -1355,13 +1355,24 @@ void MemorySSA::OptimizeUses::optimizeUsesInBlock( if (LocInfo.PopEpoch != PopEpoch) { LocInfo.PopEpoch = PopEpoch; LocInfo.StackEpoch = StackEpoch; - // If the lower bound was in the info we popped, we have to reset it. - if (LocInfo.LowerBound >= VersionStack.size()) { + // If the lower bound was in something that no longer dominates us, we + // have to reset it. + // We can't simply track stack size, because the stack may have had + // pushes/pops in the meantime. + // XXX: This is non-optimal, but only is slower cases with heavily + // branching dominator trees. To get the optimal number of queries would + // be to make lowerbound and lastkill a per-loc stack, and pop it until + // the top of that stack dominates us. This does not seem worth it ATM. + // A much cheaper optimization would be to always explore the deepest + // branch of the dominator tree first. This will guarantee this resets on + // the smallest set of blocks. + if (LocInfo.LowerBoundBlock && LocInfo.LowerBoundBlock != BB && + !DT->dominates(LocInfo.LowerBoundBlock, BB)){ // Reset the lower bound of things to check. // TODO: Some day we should be able to reset to last kill, rather than // 0. - LocInfo.LowerBound = 0; + LocInfo.LowerBoundBlock = VersionStack[0]->getBlock(); LocInfo.LastKillValid = false; } } else if (LocInfo.StackEpoch != StackEpoch) { @@ -1437,6 +1448,7 @@ void MemorySSA::OptimizeUses::optimizeUsesInBlock( MU->setDefiningAccess(VersionStack[LocInfo.LastKill]); } LocInfo.LowerBound = VersionStack.size() - 1; + LocInfo.LowerBoundBlock = BB; } } |
