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Learn IPConstProp to propagate arguments that are directly returned. Strictly
speaking these are not constant values. However, when a function always returns one of its arguments, then from the point of view of each caller the return value is constant (or at least a known value) and can be replaced. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@52397 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -145,6 +145,10 @@ bool IPCP::PropagateConstantsIntoArguments(Function &F) {
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// all callers that use those return values with the constant value. This will
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// leave in the actual return values and instructions, but deadargelim will
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// clean that up.
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//
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// Additionally if a function always returns one of its arguments directly,
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// callers will be updated to use the value they pass in directly instead of
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// using the return value.
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bool IPCP::PropagateConstantReturn(Function &F) {
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if (F.getReturnType() == Type::VoidTy)
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return false; // No return value.
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@ -188,8 +192,8 @@ bool IPCP::PropagateConstantReturn(Function &F) {
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if (isa<UndefValue>(V))
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continue;
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// Try to see if all the rets return the same constant.
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if (isa<Constant>(V)) {
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// Try to see if all the rets return the same constant or argument.
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if (isa<Constant>(V) || isa<Argument>(V)) {
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if (isa<UndefValue>(RV)) {
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// No value found yet? Try the current one.
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RetVals[i] = V;
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@ -255,6 +259,11 @@ bool IPCP::PropagateConstantReturn(Function &F) {
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if (index != -1) {
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Value *New = RetVals[index];
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if (New) {
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if (Argument *A = dyn_cast<Argument>(New))
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// Was an argument returned? Then find the corresponding argument in
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// the call instruction and use that. Add 1 to the argument number
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// to skipp the first argument (the function itself).
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New = Call->getOperand(A->getArgNo() + 1);
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Ins->replaceAllUsesWith(New);
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Ins->eraseFromParent();
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}
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