Differential D7633
New warning -Wpessimizing-move to catch when removing calls to std::move prevent optimization Authored by rtrieu on Feb 13 2015, 3:55 PM.
Details This warning will catch:
struct A {}
A test() {
A a = std::move(A()); // warn since A() is a pr-value
return std::move(a); // warn since a is a local variable
}
Diff Detail Event TimelineComment Actions I don't think it's appropriate for this warning to look at whether we would have actually performed NRVO. Instead, I would suggest modeling this as follows: when we perform initialization, and the source expression is std::move(x), and x is of class type, and either x is a prvalue or {we're initializing a return object and x is the name of a local variable or parameter of the returned type ignoring cv-qualification}, emit a warning. Comment Actions So then something like this: struct S{};
S test(bool cond) {
S s1, s2;
if (cond)
return std::move(s1);
return std::move(s2);
}would be better with the std::move's removed: struct S{};
S test(bool cond) {
S s1, s2;
if (cond)
return s1;
return s2;
}even though NRVO would not be triggered since different local variables are used?
Comment Actions Moved the check into InitiailzationSequence::Perform
Comment Actions LGTM with a couple of minor changes.
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This check is not especially cheap, and the code below will be cheap in most cases; it's probably better to omit this.