rnk accepted this revision. rnk added a comment. This revision is now accepted and ready to land.
In D152986#4426256 <https://reviews.llvm.org/D152986#4426256>, @eddyz87 wrote: > In D152986#4425736 <https://reviews.llvm.org/D152986#4425736>, @rnk wrote: > >> The purpose of the attribute is really limited to preserving source location >> information on instructions, and this isn't really a supported usage. > > But it would prevent merging, right? I understand that using this attribute > might block some legitimate optimizations. > Or do you mean that it is a "best effort" thing and not all transformations > might honor it? Essentially, yes. Anyway, I think this looks good, please apply the doc update. ================ Comment at: clang/include/clang/Basic/AttrDocs.td:551-555 calls to the specified function from merging. It has no effect on indirect calls. + +``nomerge`` attribute can be specified for pointers to functions, all +calls done through such pointer would be protected from merging. ---------------- eddyz87 wrote: > rnk wrote: > > This statement of the attribute having "no effect on indirect calls" is > > slightly confusing now that we talk about function pointers immediately > > afterward. Can you please rework this a bit, and clarify that when applied > > to function pointers, the attribute only takes effect when the call target > > is directly the variable which carries the attribute? For example, this has > > no effect: > > ``` > > void (*fp)() __attribute__((nomerge)); > > void callit() { > > auto tmp = fp; > > tmp(); > > (*fp)(); // I think TargetDecl will be null in the code, tell me if I'm > > wrong > > } > > ``` > I can make it more elaborate, would the text as below be fine? > Regarding TargetDecl value it is not null both times: > - `(VarDecl 'tmp' (ImplicitCastExpr (DeclRefExpr (Var fp))))` > - `(VarDecl 'fp')` > > --- > > ``nomerge`` attribute can also be used as function attribute to prevent all > calls to the specified function from merging. It has no effect on indirect > calls to such functions. For example: > > .. code-block:: c++ > > [[clang::nomerge]] void foo(int) {} > > void bar(int x) { > auto *ptr = foo; > if (x) foo(1); else foo(2); // will not be merged > if (x) ptr(1); else ptr(2); // indirect call, can be merged > } > > ``nomerge`` attribute can also be used for pointers to functions to > prevent calls through such pointer from merging. In such case the > effect applies only to a specific function pointer. For example: > > .. code-block:: c++ > > [[clang::nomerge]] void (*foo)(int); > > void bar(int x) { > auto *ptr = foo; > if (x) foo(1); else foo(2); // will not be merged > if (x) ptr(1); else ptr(2); // 'ptr' has no 'nomerge' attribute, > // can be merged > } > Looks good to me, thanks! Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D152986/new/ https://reviews.llvm.org/D152986 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
