Patch to optimize away copy constructor call when
appropriate. llvm-svn: 78267
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@ -256,6 +256,19 @@ CodeGenFunction::EmitCXXConstructExpr(llvm::Value *Dest,
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if (RD->hasTrivialConstructor())
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return;
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// Code gen optimization to eliminate copy constructor and return
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// its first argument instead.
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const CXXConstructorDecl *CDecl = E->getConstructor();
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if (E->getNumArgs() == 1 &&
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CDecl->isCopyConstructor(getContext())) {
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CXXConstructExpr::const_arg_iterator i = E->arg_begin();
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const Expr *SubExpr = (*i);
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// FIXME. Any other cases can be optimized away?
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if (isa<CallExpr>(SubExpr) || isa<CXXTemporaryObjectExpr>(SubExpr)) {
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EmitAggExpr(SubExpr, Dest, false);
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return;
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}
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}
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// Call the constructor.
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EmitCXXConstructorCall(E->getConstructor(), Ctor_Complete, Dest,
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E->arg_begin(), E->arg_end());
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@ -0,0 +1,31 @@
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// RUN: clang-cc -emit-llvm -o %t %s &&
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// RUN: grep "_ZN1CC1ERK1C" %t | count 0
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extern "C" int printf(...);
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struct C {
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C() : iC(6) {printf("C()\n"); }
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C(const C& c) { printf("C(const C& c)\n"); }
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int iC;
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};
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C foo() {
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return C();
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};
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class X { // ...
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public:
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X(int) {}
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X(const X&, int i = 1, int j = 2, C c = foo()) {
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printf("X(const X&, %d, %d, %d)\n", i, j, c.iC);
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}
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};
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int main()
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{
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X a(1);
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X b(a, 2);
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X c = b;
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X d(a, 5, 6);
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}
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