[llvm] r310985 - Merge debug info when hoist then-else code to if.

[Adrian Prantl via llvm-commits]

> On Aug 25, 2017, at 3:15 PM, David Blaikie <dblaikie at gmail.com> wrote:
> 
> Adrian - what were we doing about cases where merged locations were on call instructions? I think this case is one of those, where if the instruction is a call, this may drop the location from the call, then inline through the call creating corrupted debug info.

I guess that in this case the only sane thing we can do is create a new artificial line 0 location in one of the two calls' scope. It's not pretty, but that;s the best I can come up with.

-- adrian

> 
> Here's a test case that seems to exercise/assert on that (but it asserts relatively late - would be handy to have a way to run the verifier between each optimization - maybe there is such an option?):
> 
> struct string {
>   ~string();
> };
> void f2();
> void f1(int) { f2(); }
> void run(int c) {
>   string body;
>   while (true) {
>     if (c)
>       f1(c);
>     else
>       f1(c);
>   }
> }
> 
> On Tue, Aug 15, 2017 at 6:56 PM Dehao Chen via llvm-commits <llvm-commits at lists.llvm.org <mailto:llvm-commits at lists.llvm.org>> wrote:
> Author: dehao
> Date: Tue Aug 15 18:55:26 2017
> New Revision: 310985
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=310985&view=rev <http://llvm.org/viewvc/llvm-project?rev=310985&view=rev>
> Log:
> Merge debug info when hoist then-else code to if.
> 
> Summary: When we move then-else code to if, we need to merge its debug info, otherwise the hoisted instruction may have inaccurate debug info attached.
> 
> Reviewers: aprantl, probinson, dblaikie, echristo, loladiro
> 
> Reviewed By: aprantl
> 
> Subscribers: sanjoy, llvm-commits
> 
> Differential Revision: https://reviews.llvm.org/D36778 <https://reviews.llvm.org/D36778>
> 
> Added:
>     llvm/trunk/test/Transforms/SimplifyCFG/min_dbginfo.ll
> Modified:
>     llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
> 
> Modified: llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp?rev=310985&r1=310984&r2=310985&view=diff <http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp?rev=310985&r1=310984&r2=310985&view=diff>
> ==============================================================================
> --- llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp (original)
> +++ llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp Tue Aug 15 18:55:26 2017
> @@ -1336,6 +1336,8 @@ HoistTerminator:
>      I2->replaceAllUsesWith(NT);
>      NT->takeName(I1);
>    }
> +  NT->setDebugLoc(DILocation::getMergedLocation(
> +      I1->getDebugLoc(), I2->getDebugLoc()));
> 
>    IRBuilder<NoFolder> Builder(NT);
>    // Hoisting one of the terminators from our successor is a great thing.
> 
> Added: llvm/trunk/test/Transforms/SimplifyCFG/min_dbginfo.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/SimplifyCFG/min_dbginfo.ll?rev=310985&view=auto <http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/SimplifyCFG/min_dbginfo.ll?rev=310985&view=auto>
> ==============================================================================
> --- llvm/trunk/test/Transforms/SimplifyCFG/min_dbginfo.ll (added)
> +++ llvm/trunk/test/Transforms/SimplifyCFG/min_dbginfo.ll Tue Aug 15 18:55:26 2017
> @@ -0,0 +1,39 @@
> +; RUN: opt < %s -simplifycfg -S | FileCheck %s
> +
> +; Checks if the debug info is removed for the "select" instruction.
> +; CHECK: cmp {{.*}} !dbg
> +; CHECK-NOT: select {{.*}} !dbg
> +define i32 @min(i32 %a, i32 %b) {
> +entry:
> +  %cmp = icmp slt i32 %a, %b, !dbg !9
> +  br i1 %cmp, label %if.then, label %if.else, !dbg !10
> +
> +if.then:
> +  br label %return, !dbg !11
> +
> +if.else:
> +  br label %return, !dbg !12
> +
> +return:
> +  %retval.0 = phi i32 [ %a, %if.then ], [ %b, %if.else ]
> +  ret i32 %retval.0, !dbg !13
> +}
> +
> +!llvm.dbg.cu <http://llvm.dbg.cu/> = !{!0}
> +!llvm.module.flags = !{!3, !4, !5}
> +!llvm.ident = !{!6}
> +
> +!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 6.0.0 (trunk 310792)", isOptimized: true, runtimeVersion: 0, emissionKind: LineTablesOnly, enums: !2)
> +!1 = !DIFile(filename: "min.cc", directory: "/")
> +!2 = !{}
> +!3 = !{i32 2, !"Dwarf Version", i32 4}
> +!4 = !{i32 2, !"Debug Info Version", i32 3}
> +!5 = !{i32 1, !"wchar_size", i32 4}
> +!6 = !{!"clang version 6.0.0 (trunk 310792)"}
> +!7 = distinct !DISubprogram(name: "min", scope: !1, file: !1, line: 3, type: !8, isLocal: false, isDefinition: true, scopeLine: 3, flags: DIFlagPrototyped, isOptimized: true, unit: !0, variables: !2)
> +!8 = !DISubroutineType(types: !2)
> +!9 = !DILocation(line: 4, column: 8, scope: !7)
> +!10 = !DILocation(line: 4, column: 6, scope: !7)
> +!11 = !DILocation(line: 5, column: 3, scope: !7)
> +!12 = !DILocation(line: 7, column: 3, scope: !7)
> +!13 = !DILocation(line: 9, column: 1, scope: !7)
> 
> 
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