[llvm] r245588 - Fix a debug location handling bug in GVN.
Adrian Prantl via llvm-commits
llvm-commits at lists.llvm.org
Thu Aug 20 11:40:13 PDT 2015
> On Aug 20, 2015, at 11:34 AM, David Blaikie <dblaikie at gmail.com> wrote:
>
>
>
> On Thu, Aug 20, 2015 at 11:23 AM, Adrian Prantl via llvm-commits <llvm-commits at lists.llvm.org <mailto:llvm-commits at lists.llvm.org>> wrote:
> Author: adrian
> Date: Thu Aug 20 13:23:56 2015
> New Revision: 245588
>
> URL: http://llvm.org/viewvc/llvm-project?rev=245588&view=rev <https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject-3Frev-3D245588-26view-3Drev&d=BQMFaQ&c=eEvniauFctOgLOKGJOplqw&r=cTx6f1tAfqPeajYunFWp7_8ot79RnHyNteqzig4fXmA&m=86dqHw1S-sgpsH4Bsgqx_Mj5aCBM3RvAtP4OlFh1AG0&s=e4jjdKwbnVmqzlwu17oTd4tnkT7mzpB7ff782guZhFo&e=>
> Log:
> Fix a debug location handling bug in GVN.
> Caught by the famous "DebugLoc describes the currect SubProgram" assertion.
>
> Huzzah! \o/ ;) (sorry, I know they're a pain to track down, but it's a great way to find debug info quality bugs that would produce really shitty debug info if it weren't for this assertion)
Oh yes.
>
> When GVN is removing a nonlocal load it updates the debug location of the
> SSA value it replaced the load with with the one of the load.
>
> I guess I'm not quite following here (knowing next to nothing about GVN) - could you explain this in more detail? What transformation is GVN performing on a call?
GVN is eliminating the load (and store) to @f and replaces all uses of the load with the value that is stored in @f, which is %call. It then used to transfer the DebugLoc of the load to the value it’s replacing it with (in this case %call). This triggers the assertion because %call happens to be, well, a call.
>
> In the
> testcase this actually overwrites a valid debug location with an empty one.
>
> In reality GVN has to make an arbitrary choice between two equally valid
> debug locations. This patch changes to behavior to only update the
> location if the value doesn't already have a debug location.
>
> Added:
> llvm/trunk/test/DebugInfo/gvn.ll
> Modified:
> llvm/trunk/lib/Transforms/Scalar/GVN.cpp
>
> Modified: llvm/trunk/lib/Transforms/Scalar/GVN.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/GVN.cpp?rev=245588&r1=245587&r2=245588&view=diff <https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject_llvm_trunk_lib_Transforms_Scalar_GVN.cpp-3Frev-3D245588-26r1-3D245587-26r2-3D245588-26view-3Ddiff&d=BQMFaQ&c=eEvniauFctOgLOKGJOplqw&r=cTx6f1tAfqPeajYunFWp7_8ot79RnHyNteqzig4fXmA&m=86dqHw1S-sgpsH4Bsgqx_Mj5aCBM3RvAtP4OlFh1AG0&s=3z-a-gXHRfLinlwxZW5mohZaeBGnPUqI5NluJhV-TAQ&e=>
> ==============================================================================
> --- llvm/trunk/lib/Transforms/Scalar/GVN.cpp (original)
> +++ llvm/trunk/lib/Transforms/Scalar/GVN.cpp Thu Aug 20 13:23:56 2015
> @@ -1744,7 +1744,8 @@ bool GVN::processNonLocalLoad(LoadInst *
> if (isa<PHINode>(V))
> V->takeName(LI);
> if (Instruction *I = dyn_cast<Instruction>(V))
> - I->setDebugLoc(LI->getDebugLoc());
> + if (LI->getDebugLoc())
> + I->setDebugLoc(LI->getDebugLoc());
> if (V->getType()->getScalarType()->isPointerTy())
> MD->invalidateCachedPointerInfo(V);
> markInstructionForDeletion(LI);
>
> Added: llvm/trunk/test/DebugInfo/gvn.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/DebugInfo/gvn.ll?rev=245588&view=auto <https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject_llvm_trunk_test_DebugInfo_gvn.ll-3Frev-3D245588-26view-3Dauto&d=BQMFaQ&c=eEvniauFctOgLOKGJOplqw&r=cTx6f1tAfqPeajYunFWp7_8ot79RnHyNteqzig4fXmA&m=86dqHw1S-sgpsH4Bsgqx_Mj5aCBM3RvAtP4OlFh1AG0&s=zFB2qrxGTG9FAm3X7GplKYZ_JKT6reaieKBiMl66Dzs&e=>
> ==============================================================================
> --- llvm/trunk/test/DebugInfo/gvn.ll (added)
> +++ llvm/trunk/test/DebugInfo/gvn.ll Thu Aug 20 13:23:56 2015
> @@ -0,0 +1,135 @@
> +; RUN: opt < %s -O2 -gvn -S | FileCheck %s
> +;
> +; Produced at -O2 from:
>
> Do you have the original reproduction -cc1 line, by chance? I'd be curious to see if this test case can be simplified a bit further to make the interesting part(s) more obvious.
Testcase-golfing! :-)
It’s very hard to reduce it any more from source, because it needs this specific chain of simplify-cfg and gvn:
clang -cc1 -triple arm64-apple-ios -emit-llvm -gdwarf-2 -O2 file.c -o -
-- adrian
> +; struct context {
> +; int cur_pid
> +; };
> +; int a, b, c, f, d;
> +; int pid_for_task(int);
> +; sample(struct context *p1)
> +; {
> +; if (c)
> +; b = a;
> +; if (a && p1->cur_pid)
> +; sample_internal();
> +; }
> +; callback() {
> +; f = pid_for_task(d);
> +; sample(&f);
> +; }
> +
> +target datalayout = "e-m:o-i64:64-i128:128-n32:64-S128"
> +target triple = "arm64-apple-ios"
> +
> +%struct.context = type { i32 }
> +
> + at c = common global i32 0, align 4
> + at a = common global i32 0, align 4
> + at b = common global i32 0, align 4
> + at d = common global i32 0, align 4
> + at f = common global i32 0, align 4
> +
> +; Function Attrs: nounwind
> +declare i32 @sample_internal(...)
> +
> +; Function Attrs: nounwind
> +define i32 @callback() #0 {
> +entry:
> + %0 = load i32, i32* @d, align 4, !dbg !37
> +
> + ; Verify that the call still has a debug location after GVN.
> + ; CHECK: %call = tail call i32 @pid_for_task(i32 %0) #{{[0-9]}}, !dbg
> + %call = tail call i32 @pid_for_task(i32 %0) #3, !dbg !37
> +
> + store i32 %call, i32* @f, align 4, !dbg !37
> + tail call void @llvm.dbg.value(metadata %struct.context* bitcast (i32* @f to %struct.context*), i64 0, metadata !25, metadata !26) #3, !dbg !38
> + %1 = load i32, i32* @c, align 4, !dbg !40
> + %tobool.i = icmp eq i32 %1, 0, !dbg !40
> + %.pr.i = load i32, i32* @a, align 4, !dbg !41
> + br i1 %tobool.i, label %if.end.i, label %if.then.i, !dbg !42
> +
> +if.then.i: ; preds = %entry
> + store i32 %.pr.i, i32* @b, align 4, !dbg !43
> + br label %if.end.i, !dbg !43
> +
> +if.end.i: ; preds = %if.then.i, %entry
> + %tobool1.i = icmp eq i32 %.pr.i, 0, !dbg !41
> +
> + ; This instruction has no debug location -- in this
> + ; particular case it was removed by a bug in SimplifyCFG.
> + %2 = load i32, i32* @f, align 4
> +
> + ; GVN is supposed to replace the load of @f with a direct reference to %call.
> + ; CHECK: %tobool2.i = icmp eq i32 %call, 0, !dbg
> + %tobool2.i = icmp eq i32 %2, 0, !dbg !41
> +
> + %or.cond = or i1 %tobool1.i, %tobool2.i, !dbg !41
> + br i1 %or.cond, label %sample.exit, label %if.then.3.i, !dbg !41
> +
> +if.then.3.i: ; preds = %if.end.i
> + %call.i = tail call i32 bitcast (i32 (...)* @sample_internal to i32 ()*)() #3, !dbg !44
> + br label %sample.exit, !dbg !44
> +
> +sample.exit: ; preds = %if.end.i, %if.then.3.i
> + ret i32 undef, !dbg !45
> +}
> +
> +declare i32 @pid_for_task(i32) #1
> +
> +; Function Attrs: nounwind readnone
> +declare void @llvm.dbg.value(metadata, i64, metadata, metadata) #2
> +
> +attributes #0 = { nounwind }
> +attributes #2 = { nounwind readnone }
> +attributes #3 = { nounwind }
> +
> +!llvm.dbg.cu <https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.dbg.cu&d=BQMFaQ&c=eEvniauFctOgLOKGJOplqw&r=cTx6f1tAfqPeajYunFWp7_8ot79RnHyNteqzig4fXmA&m=86dqHw1S-sgpsH4Bsgqx_Mj5aCBM3RvAtP4OlFh1AG0&s=k1mLTSIzssOjZljHe612mvR_uLJjrT9NK96QRAUNl_Q&e=> = !{!0}
> +!llvm.module.flags = !{!22, !23}
> +!llvm.ident = !{!24}
> +
> +!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 3.8.0 (trunk 244473) (llvm/trunk 244644)", isOptimized: false, runtimeVersion: 0, emissionKind: 1, enums: !2, subprograms: !3, globals: !16)
> +!1 = !DIFile(filename: "test.c", directory: "/")
> +!2 = !{}
> +!3 = !{!4, !13}
> +!4 = !DISubprogram(name: "sample", scope: !5, file: !5, line: 6, type: !6, isLocal: false, isDefinition: true, scopeLine: 7, flags: DIFlagPrototyped, isOptimized: false, variables: !2)
> +!5 = !DIFile(filename: "test.i", directory: "/")
> +!6 = !DISubroutineType(types: !7)
> +!7 = !{!8, !9}
> +!8 = !DIBasicType(name: "int", size: 32, align: 32, encoding: DW_ATE_signed)
> +!9 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !10, size: 64, align: 64)
> +!10 = !DICompositeType(tag: DW_TAG_structure_type, name: "context", file: !5, line: 1, size: 32, align: 32, elements: !11)
> +!11 = !{!12}
> +!12 = !DIDerivedType(tag: DW_TAG_member, name: "cur_pid", scope: !10, file: !5, line: 2, baseType: !8, size: 32, align: 32)
> +!13 = !DISubprogram(name: "callback", scope: !5, file: !5, line: 13, type: !14, isLocal: false, isDefinition: true, scopeLine: 13, isOptimized: false, function: i32 ()* @callback, variables: !2)
> +!14 = !DISubroutineType(types: !15)
> +!15 = !{!8}
> +!16 = !{!17, !18, !19, !20, !21}
> +!17 = !DIGlobalVariable(name: "a", scope: !0, file: !5, line: 4, type: !8, isLocal: false, isDefinition: true, variable: i32* @a)
> +!18 = !DIGlobalVariable(name: "b", scope: !0, file: !5, line: 4, type: !8, isLocal: false, isDefinition: true, variable: i32* @b)
> +!19 = !DIGlobalVariable(name: "c", scope: !0, file: !5, line: 4, type: !8, isLocal: false, isDefinition: true, variable: i32* @c)
> +!20 = !DIGlobalVariable(name: "f", scope: !0, file: !5, line: 4, type: !8, isLocal: false, isDefinition: true, variable: i32* @f)
> +!21 = !DIGlobalVariable(name: "d", scope: !0, file: !5, line: 4, type: !8, isLocal: false, isDefinition: true, variable: i32* @d)
> +!22 = !{i32 2, !"Dwarf Version", i32 2}
> +!23 = !{i32 2, !"Debug Info Version", i32 3}
> +!24 = !{!"clang version 3.8.0 (trunk 244473) (llvm/trunk 244644)"}
> +!25 = !DILocalVariable(name: "p1", arg: 1, scope: !4, file: !5, line: 6, type: !9)
> +!26 = !DIExpression()
> +!27 = !DILocation(line: 6, scope: !4)
> +!28 = !DILocation(line: 8, scope: !29)
> +!29 = distinct !DILexicalBlock(scope: !4, file: !5, line: 8)
> +!30 = !DILocation(line: 10, scope: !31)
> +!31 = distinct !DILexicalBlock(scope: !4, file: !5, line: 10)
> +!32 = !DILocation(line: 8, scope: !4)
> +!33 = !DILocation(line: 9, scope: !29)
> +!34 = !DILocation(line: 10, scope: !4)
> +!35 = !DILocation(line: 11, scope: !31)
> +!36 = !DILocation(line: 12, scope: !4)
> +!37 = !DILocation(line: 14, scope: !13)
> +!38 = !DILocation(line: 6, scope: !4, inlinedAt: !39)
> +!39 = distinct !DILocation(line: 15, scope: !13)
> +!40 = !DILocation(line: 8, scope: !29, inlinedAt: !39)
> +!41 = !DILocation(line: 10, scope: !31, inlinedAt: !39)
> +!42 = !DILocation(line: 8, scope: !4, inlinedAt: !39)
> +!43 = !DILocation(line: 9, scope: !29, inlinedAt: !39)
> +!44 = !DILocation(line: 11, scope: !31, inlinedAt: !39)
> +!45 = !DILocation(line: 16, scope: !13)
>
>
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