Enhance SROA to "promote to scalar" allocas which are
memcpy/memmove'd into or out of. This fixes a serious
perf issue that Nate ran into.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@66366 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/ScalarReplAggregates.cpp b/lib/Transforms/Scalar/ScalarReplAggregates.cpp
index 644625f..98d5a02 100644
--- a/lib/Transforms/Scalar/ScalarReplAggregates.cpp
+++ b/lib/Transforms/Scalar/ScalarReplAggregates.cpp
@@ -1356,6 +1356,16 @@
continue;
}
}
+
+ // If this is a memcpy or memmove into or out of the whole allocation, we
+ // can handle it like a load or store of the scalar type.
+ if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(User)) {
+ if (ConstantInt *Len = dyn_cast<ConstantInt>(MTI->getLength()))
+ if (Len->getZExtValue() == AllocaSize && Offset == 0) {
+ IsNotTrivial = true;
+ continue;
+ }
+ }
// Ignore dbg intrinsic.
if (isa<DbgInfoIntrinsic>(User))
@@ -1440,6 +1450,44 @@
MSI->eraseFromParent();
continue;
}
+
+ // If this is a memcpy or memmove into or out of the whole allocation, we
+ // can handle it like a load or store of the scalar type.
+ if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(User)) {
+ assert(Offset == 0 && "must be store to start of alloca");
+
+ // If the source and destination are both to the same alloca, then this is
+ // a noop copy-to-self, just delete it. Otherwise, emit a load and store
+ // as appropriate.
+ AllocaInst *OrigAI = cast<AllocaInst>(Ptr->getUnderlyingObject());
+
+ if (MTI->getSource()->getUnderlyingObject() != OrigAI) {
+ // Dest must be OrigAI, change this to be a load from the original
+ // pointer (bitcasted), then a store to our new alloca.
+ assert(MTI->getRawDest() == Ptr && "Neither use is of pointer?");
+ Value *SrcPtr = MTI->getSource();
+ SrcPtr = Builder.CreateBitCast(SrcPtr, NewAI->getType());
+
+ LoadInst *SrcVal = Builder.CreateLoad(SrcPtr, "srcval");
+ SrcVal->setAlignment(MTI->getAlignment());
+ Builder.CreateStore(SrcVal, NewAI);
+ } else if (MTI->getDest()->getUnderlyingObject() != OrigAI) {
+ // Src must be OrigAI, change this to be a load from NewAI then a store
+ // through the original dest pointer (bitcasted).
+ assert(MTI->getRawSource() == Ptr && "Neither use is of pointer?");
+ LoadInst *SrcVal = Builder.CreateLoad(NewAI, "srcval");
+
+ Value *DstPtr = Builder.CreateBitCast(MTI->getDest(), NewAI->getType());
+ StoreInst *NewStore = Builder.CreateStore(SrcVal, DstPtr);
+ NewStore->setAlignment(MTI->getAlignment());
+ } else {
+ // Noop transfer. Src == Dst
+ }
+
+
+ MTI->eraseFromParent();
+ continue;
+ }
// If user is a dbg info intrinsic then it is safe to remove it.
if (isa<DbgInfoIntrinsic>(User)) {