nickdesaulniers added a comment. In D74094#4643495 <https://reviews.llvm.org/D74094#4643495>, @rjmccall wrote:
> I can't easily tell you because the "standalone example" involves a million > templates that I don't know anything about, and nobody seems to have done the > analysis to identify the specific source of the miscompile. Sure; @alexfh @vitalybuka can you both please help produce a further reduced test case from https://reviews.llvm.org/D74094#4633799 ? Otherwise I'm beginning to think this patch may have been reverted prematurely; before an understood + reduced test case was reduced. > What I can tell you is that there is an enormous semantic difference between > passing a pr-value argument to a parameter that's passed by reference and to > a parameter that's passed by value. In the former case, the reference is > bound to a temporary with full-expression lifetime, and it is totally > reasonable to return its address. In the latter case, the parameter object > will often have a lifetime bound by the current function, and you cannot > return its address without it being UB. I'm trying to come up with an example of "the former." struct foo { int x; }; // Returns a reference to the minimum foo. foo &min(foo &a, foo &b); void consume (foo&); void bar () { consume(min(foo{0}, foo{1})); } doesn't compile: foo.cpp:11:11: error: no matching function for call to 'min' 11 | consume(min(foo{0}, foo{1})); | ^~~ foo.cpp:6:6: note: candidate function not viable: expects an lvalue for 1st argument 6 | foo &min(foo &a, foo &b); | ^ ~~~~~~ Have I misinterpreted what you meant by "passing a pr-value argument to a parameter that's passed by reference?" > Looking closer, my previous guess that this was accidentally triggering for > reference parameters seems to be wrong, because that case is filtered out > earlier in the function. I'm not sure what the problem is exactly, then, > unless the code indeed has UB. In which case, perhaps this was reverted prematurely. Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D74094/new/ https://reviews.llvm.org/D74094 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
