arsenm added a comment. In D86020#2222103 <https://reviews.llvm.org/D86020#2222103>, @atrosinenko wrote:
> @rjmccall > > Maybe I overestimated similarity of `byval` and recently introduced > `byref`... Looks like some aliasing restrictions are not mentioned in LLVM > Language Reference <https://llvm.org/docs/LangRef.html#parameter-attributes>. > For example, the only way for Clang to emit the `byref` attribute to LLVM IR > I know about is via `ABIArgInfo` with `Kind == IndirectAliased` introduced in > D79744: clang: Use byref for aggregate kernel arguments > <https://reviews.llvm.org/D79744> - and it has a note that "The object is > known to not be through any other references for the duration of the call, > and the callee must not itself modify the object". This seems to be necessary > for correctness of this transformation. If LLVM Language Reference does not > mention such restrictions intentionally, then it may be clang that should be > responsible for such optimizations. I think this lost the word written or stored ================ Comment at: llvm/test/Transforms/MemCpyOpt/byref-memcpy.ll:8 +; A caller of this function has to arrange everything for the pointer it passes +; to be usable with byref attrbiute anyway, so just pass the pointer through. +define void @function_with_byref_arg(%struct.S* byref(%struct.S) align 4 %0) { ---------------- Typo attrbiute ================ Comment at: llvm/test/Transforms/MemCpyOpt/byref-memcpy.ll:55 +; CHECK-NEXT: [[V2:%.+]] = bitcast %struct.S* [[V0]] to i8* +; CHECK-NEXT: call void @llvm.memcpy.p0i8.p0i8.i16(i8* align 4 [[V1]], i8* align 2 [[V2]], i16 16, i1 false) +; CHECK-NEXT: call void @leaf(%struct.S* byref(%struct.S) align 4 [[ALLOCA]]) ---------------- atrosinenko wrote: > Interestingly, if I change the alignment of the second argument from 2 back > to 4, then memcpy() is successfully dropped (as if everything has big-enough > alignment) while it seemingly shouldn't be. Is it just due to the code being > ill-formed? I'm not sure I follow, if you change it to 4 it is big enough? Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D86020/new/ https://reviews.llvm.org/D86020 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
