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<p class="MsoNormal">Hi Neil,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">This should be solved with the 'full restrict patches' <a href="https://reviews.llvm.org/D68484">
https://reviews.llvm.org/D68484</a> : it treats %noalias arguments in a different<o:p></o:p></p>
<p class="MsoNormal">way so that we keep more accurate information during SROA.<o:p></o:p></p>
<p class="MsoNormal">A convenience single patch is available here: <a href="https://reviews.llvm.org/D69542">
https://reviews.llvm.org/D69542</a><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Please let me know, if you happen to try it out, that it indeed solves your problem.<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">Jeroen Dobbelaere<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><b>From:</b> llvm-dev <llvm-dev-bounces@lists.llvm.org> <b>On Behalf Of
</b>Neil Henning via llvm-dev<br>
<b>Sent:</b> Friday, January 17, 2020 17:22<br>
<b>To:</b> llvm-dev <llvm-dev@lists.llvm.org><br>
<b>Subject:</b> [llvm-dev] Help with SROA throwing away no-alias information<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I'm having an issue where SROA will throw away no-alias information on some loads after inlining, because the loads are derived from a store to an alloca which can be removed after inlining.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">The pointers that were originally stored into the alloca do <b>
not </b>have any aliasing information - the only context that allowed me to assert aliasing was that the inlined-function guaranteed it to be so.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I know why SROA has done this - its just removing a store -> load on an alloca by forwarding the store, but is there anyway I can preserve the information that these pointers must no-alias?<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Here is the pre/post from when SROA is run and you can see the now missing information of no-alias:<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New"">define dllexport void @"Burst.Compiler.IL.Tests.Aliasing.CheckInlinedFunctionPreservesAliasing(ref Burst.Compiler.IL.Tests.Aliasing.NoAliasWithContentsStruct s)_862A52BC559AC318"(%"Burst.Compiler.IL.Tests.Aliasing/NoAliasWithContentsStruct"*
nocapture nonnull readonly %s) local_unnamed_addr #0 !ubaa. !1 {<br>
entry:<br>
%var.0 = alloca %"Burst.Compiler.IL.Tests.Aliasing/NoAliasField", align 8<br>
%0 = bitcast %"Burst.Compiler.IL.Tests.Aliasing/NoAliasWithContentsStruct"* %s to i64*<br>
%1 = load i64, i64* %0, align 1<br>
%2 = getelementptr %"Burst.Compiler.IL.Tests.Aliasing/NoAliasWithContentsStruct", %"Burst.Compiler.IL.Tests.Aliasing/NoAliasWithContentsStruct"* %s, i64 0, i32 1<br>
%3 = bitcast i8** %2 to i64*<br>
%4 = load i64, i64* %3, align 1<br>
%5 = bitcast %"Burst.Compiler.IL.Tests.Aliasing/NoAliasField"* %var.0 to i64*<br>
store i64 %1, i64* %5, align 8<br>
%.fca.1.gep = getelementptr inbounds %"Burst.Compiler.IL.Tests.Aliasing/NoAliasField", %"Burst.Compiler.IL.Tests.Aliasing/NoAliasField"* %var.0, i64 0, i32 1<br>
%6 = bitcast i32** %.fca.1.gep to i64*<br>
store i64 %4, i64* %6, align 8<br>
%7 = bitcast %"Burst.Compiler.IL.Tests.Aliasing/NoAliasField"* %var.0 to i8**<br>
%8 = load i8*, i8** %7, align 1, !alias.scope !2, !noalias !5<br>
%9 = getelementptr %"Burst.Compiler.IL.Tests.Aliasing/NoAliasField", %"Burst.Compiler.IL.Tests.Aliasing/NoAliasField"* %var.0, i64 0, i32 1<br>
%10 = bitcast i32** %9 to i8**<br>
%11 = load i8*, i8** %10, align 1, !alias.scope !5, !noalias !2<br>
call void @llvm.ubaa.expect.no.alias(i8* %8, i64 -1, i8* %11, i64 -1, metadata !"C:\\Users\\NeilHenning\\Home\\burst\\src\\Burst.Compiler.IL.Tests\\Shared\\083-Aliasing.cs(229,9): ") #0<br>
ret void<br>
}<br>
*** IR Dump After SROA ***<br>
; Function Attrs: nounwind<br>
define dllexport void @"Burst.Compiler.IL.Tests.Aliasing.CheckInlinedFunctionPreservesAliasing(ref Burst.Compiler.IL.Tests.Aliasing.NoAliasWithContentsStruct s)_862A52BC559AC318"(%"Burst.Compiler.IL.Tests.Aliasing/NoAliasWithContentsStruct"* nocapture nonnull
readonly %s) local_unnamed_addr #0 !ubaa. !1 {<br>
entry:<br>
%0 = bitcast %"Burst.Compiler.IL.Tests.Aliasing/NoAliasWithContentsStruct"* %s to i64*<br>
%1 = load i64, i64* %0, align 1<br>
%2 = getelementptr %"Burst.Compiler.IL.Tests.Aliasing/NoAliasWithContentsStruct", %"Burst.Compiler.IL.Tests.Aliasing/NoAliasWithContentsStruct"* %s, i64 0, i32 1<br>
%3 = bitcast i8** %2 to i64*<br>
%4 = load i64, i64* %3, align 1<br>
%5 = inttoptr i64 %1 to i8*<br>
%6 = inttoptr i64 %4 to i8*<br>
call void @llvm.ubaa.expect.no.alias(i8* %5, i64 -1, i8* %6, i64 -1, metadata !"C:\\Users\\NeilHenning\\Home\\burst\\src\\Burst.Compiler.IL.Tests\\Shared\\083-Aliasing.cs(229,9): ") #0<br>
ret void<br>
}</span><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">My only workaround I can dream up locally is to run a pass before SROA to do the alias.scope and noalias forwarding myself by looking back through the store...<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Cheers,<o:p></o:p></p>
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<p class="MsoNormal">-Neil.<o:p></o:p></p>
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<p class="MsoNormal"><br>
-- <o:p></o:p></p>
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<p class="MsoNormal" style="line-height:11.25pt"><b><span style="font-size:10.5pt;font-family:"Arial",sans-serif;color:black">Neil Henning<o:p></o:p></span></b></p>
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<p class="MsoNormal" style="line-height:11.25pt"><span style="font-size:10.5pt;font-family:"Arial",sans-serif;color:black">Senior Software Engineer Compiler<o:p></o:p></span></p>
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<p class="MsoNormal" style="line-height:11.25pt"><span style="font-size:9.0pt;font-family:"Arial",sans-serif;color:black"><a href="https://urldefense.proofpoint.com/v2/url?u=http-3A__unity.com&d=DwMFaQ&c=DPL6_X_6JkXFx7AXWqB0tg&r=ELyOnT0WepII6UnFk-OSzxlGOXXSfAvOLT6E8iPwwJk&m=GSznZd2GUUZ6h5fLXYaTzhCHJwxEUo_GmtRYcMlOqPE&s=LVQA9YOzUMXrvsXSngTfQjveFSvNuRSG_C0S27GAu1w&e=" target="_blank">unity.com</a><o:p></o:p></span></p>
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