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slightly simplify code and substantially improve comment. Instead of
saying "it would be bad", give an example of what is going on. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@119695 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -712,34 +712,37 @@ bool MemCpyOpt::processMemCpyMemCpyDependence(MemCpyInst *M, MemCpyInst *MDep,
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// the alignment past what can be read from or written to.
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// TODO: Is this worth it if we're creating a less aligned memcpy? For
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// example we could be moving from movaps -> movq on x86.
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unsigned Align = std::min(MDep->getAlignmentCst()->getZExtValue(),
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M->getAlignmentCst()->getZExtValue());
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LLVMContext &Context = M->getContext();
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ConstantInt *AlignCI = ConstantInt::get(Type::getInt32Ty(Context), Align);
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unsigned Align = std::min(MDep->getAlignment(), M->getAlignment());
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Value *Args[5] = {
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M->getRawDest(), MDep->getRawSource(), M->getLength(),
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AlignCI, M->getVolatileCst()
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M->getRawDest(),
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MDep->getRawSource(),
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M->getLength(),
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ConstantInt::get(Type::getInt32Ty(M->getContext()), Align),
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M->getVolatileCst()
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};
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CallInst *C = CallInst::Create(MemCpyFun, Args, Args+5, "", M);
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MemoryDependenceAnalysis &MD = getAnalysis<MemoryDependenceAnalysis>();
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// If C and M don't interfere, then this is a valid transformation. If they
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// did, this would mean that the two sources overlap, which would be bad.
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MemDepResult dep = MD.getDependency(C);
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if (dep.isClobber() && dep.getInst() == MDep) {
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MD.removeInstruction(M);
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M->eraseFromParent();
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++NumMemCpyInstr;
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return true;
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// Verify that the copied-from memory doesn't change in between the two
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// transfers. For example, in:
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// memcpy(a <- b)
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// *b = 42;
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// memcpy(c <- a)
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// It would be invalid to transform the second memcpy into memcpy(c <- b).
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MemDepResult NewDep = MD.getDependency(C);
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if (!NewDep.isClobber() || NewDep.getInst() != MDep) {
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MD.removeInstruction(C);
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C->eraseFromParent();
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return false;
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}
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// Otherwise, there was no point in doing this, so we remove the call we
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// inserted and act like nothing happened.
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MD.removeInstruction(C);
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C->eraseFromParent();
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return false;
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// Otherwise we're good! Nuke the instruction we're replacing.
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MD.removeInstruction(M);
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M->eraseFromParent();
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++NumMemCpyInstr;
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return true;
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}
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