Revert r50441. The original code was correct. Add some more comments so that I don't make the same mistake in the future.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@50446 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/MemCpyOptimizer.cpp b/lib/Transforms/Scalar/MemCpyOptimizer.cpp
index 9a39c8f..d6e5f39 100644
--- a/lib/Transforms/Scalar/MemCpyOptimizer.cpp
+++ b/lib/Transforms/Scalar/MemCpyOptimizer.cpp
@@ -668,18 +668,24 @@
CallInst* C = CallInst::Create(MemCpyFun, args.begin(), args.end(), "", M);
+
+ // If C and M don't interfere, then this is a valid transformation. If they
+ // did, this would mean that the two sources overlap, which would be bad.
if (MD.getDependency(C) == MDep) {
MD.dropInstruction(M);
M->eraseFromParent();
+
+ NumMemCpyInstr++;
+
return true;
}
+ // Otherwise, there was no point in doing this, so we remove the call we
+ // inserted and act like nothing happened.
MD.removeInstruction(C);
C->eraseFromParent();
- NumMemCpyInstr++;
-
- return true;
+ return false;
}
// MemCpyOpt::runOnFunction - This is the main transformation entry point for a