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<p class="MsoNormal">Hi,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I’m trying to figure out if this behavior by Instcombine is ok, and I’d appreciate some feedback.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Suppose you have this kind of struct:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"> %struct.State = type { i32, i32, i32, i32, %"struct.State::InnerState" }<o:p></o:p></p>
<p class="MsoNormal"> %"struct.State::InnerState" = type { i32, i32 }<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Now suppose we have %S which is of type struct.State and we want to use two llvm.ptr.annotations:<o:p></o:p></p>
<p class="MsoNormal">1- one to annotate the last member of struct.State (which is of type struct.State::InnerState)<o:p></o:p></p>
<p class="MsoNormal">2- one to annotate the first member of %"struct.State::InnerState"<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">This is the IR out of clang:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">define i32 @foo(%struct.State* %S) {<o:p></o:p></p>
<p class="MsoNormal"> %my_inner_state = getelementptr inbounds %struct.State, %struct.State* %S, i32 0, i32 4<o:p></o:p></p>
<p class="MsoNormal"> %0 = bitcast %"struct.State::InnerState"* %my_inner_state to i8*<o:p></o:p></p>
<p class="MsoNormal"> %1 = call i8* @llvm.ptr.annotation.p0i8(i8* %0, i8* getelementptr inbounds ([8 x i8], [8 x i8]* @.str.4, i32 0, i32 0), i8* getelementptr inbounds ([13 x i8], [13 x i8]* @.str.1, i32 0, i32 0), i32 20)<o:p></o:p></p>
<p class="MsoNormal"> %2 = bitcast i8* %1 to %"struct.State::InnerState"*<o:p></o:p></p>
<p class="MsoNormal"> <b>%inner_member = getelementptr inbounds %"struct.State::InnerState", %"struct.State::InnerState"* %2, i32 0, i32 0<o:p></o:p></b></p>
<p class="MsoNormal"><b> %3 = bitcast i32* %inner_member to i8*<o:p></o:p></b></p>
<p class="MsoNormal"> %4 = call i8* @llvm.ptr.annotation.p0i8(i8* %3, i8* getelementptr inbounds ([8 x i8], [8 x i8]* @.str.5, i32 0, i32 0), i8* getelementptr inbounds ([13 x i8], [13 x i8]* @.str.1, i32 0, i32 0), i32 15)<o:p></o:p></p>
<p class="MsoNormal">}<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Instcombine is replacing the GEP with all 0 indices + bitcast with the base pointer of the GEP:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"> %my_inner_state = getelementptr inbounds %struct.State, %struct.State* %S, i64 0, i32 4<o:p></o:p></p>
<p class="MsoNormal"> %0 = bitcast %"struct.State::InnerState"* %my_inner_state to i8*<o:p></o:p></p>
<p class="MsoNormal"> %1 = call i8* @llvm.ptr.annotation.p0i8(i8* %0, i8* getelementptr inbounds ([8 x i8], [8 x i8]* @.str.4, i64 0, i64 0), i8* getelementptr inbounds ([13 x i8], [13 x i8]* @.str.1, i64 0, i64 0), i32 20)<o:p></o:p></p>
<p class="MsoNormal"> %2 = call i8* @llvm.ptr.annotation.p0i8(i8* %1, i8* getelementptr inbounds ([8 x i8], [8 x i8]* @.str.5, i64 0, i64 0), i8* getelementptr inbounds ([13 x i8], [13 x i8]* @.str.1, i64 0, i64 0), i32 15)<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Now we cannot distinguish between what is actually being annotated. In other words, it looks like the whole %"struct.State::InnerState” is being annotated twice.<o:p></o:p></p>
<p class="MsoNormal">Is this ok?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thanks!<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">--<o:p></o:p></p>
<p class="MsoNormal">Felipe de Azevedo Piovezan<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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