[PATCH] D41400: [MemCpyOpt] Perform call slot optimizations through GEPs

[Eli Friedman via Phabricator via llvm-commits]

efriedma added inline comments.


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Comment at: lib/Transforms/Scalar/MemCpyOptimizer.cpp:836
+  // The store to dest may never happen if the call can throw.
+  if (C->mayThrow() && !isa<AllocaInst>(cpyDest))
+    return false;
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You probably want to clarify why an alloca is special here.

Does it matter if cpyDest could be accessed from another thread?

Do you need to check whether any calls between "C" and "cpy" could throw?


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Comment at: lib/Transforms/Scalar/MemCpyOptimizer.cpp:848
+    APInt APOffset(DL.getPointerSizeInBits(GEP->getPointerAddressSpace()), 0);
+    if (GEP->accumulateConstantOffset(DL, APOffset) && !Offset.isNegative()) {
+      auto Offset = APOffset.getSExtValue();
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Maybe this code belongs in getPointerDereferenceableBytes, rather than here?


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Comment at: lib/Transforms/Scalar/MemCpyOptimizer.cpp:915
+      if (auto G = dyn_cast<GetElementPtrInst>(cpyDest)) {
+        auto P = G->getPointerOperand();
+        auto PI = dyn_cast<Instruction>(P);
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This check is kind of fragile, in that it assumes the other operands to the GEP are all ConstantInts.


https://reviews.llvm.org/D41400