[llvm] r245588 - Fix a debug location handling bug in GVN.

Thu Aug 20 17:01:23 PDT 2015

Nice, I updated the derived IR in r245642 based on that!

thanks,
adrian

> On Aug 20, 2015, at 4:15 PM, David Blaikie <dblaikie at gmail.com> wrote:
> 
> Got it a bit shorter, but not necessarily more obvious... I assume the inlining is necessary, so probably good to use __attribute__((always_inline) on that nested function. not sure what else.
> 
> int a, b;
> void f1(int *p1) {
>   if (b)
>     a = 1;
>   if (a && *p1)
>     f4();
> }
> int f2(int);
> void f3(void) {
>   a = f2(1);
>   f1(&a);
> }
> 
> 
> 
> 
> On Thu, Aug 20, 2015 at 2:10 PM, David Blaikie <dblaikie at gmail.com <mailto:dblaikie at gmail.com>> wrote:
> 
> 
> On Thu, Aug 20, 2015 at 2:01 PM, Adrian Prantl <aprantl at apple.com <mailto:aprantl at apple.com>> wrote:
> 
> > On Aug 20, 2015, at 12:27 PM, David Blaikie <dblaikie at gmail.com <mailto:dblaikie at gmail.com>> wrote:
> >
> >
> >
> > On Thu, Aug 20, 2015 at 11:40 AM, Adrian Prantl <aprantl at apple.com <mailto:aprantl at apple.com>> wrote:
> >
> >> On Aug 20, 2015, at 11:34 AM, David Blaikie <dblaikie at gmail.com <mailto: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=eNYrr5T4YMj8KPepXAE5fV644gwPkXJumvSKDpUcf-Q&s=pqsDWhgFCUgfHJEtpw2PC6mTXOMru2yufvCRXtok1B8&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=eNYrr5T4YMj8KPepXAE5fV644gwPkXJumvSKDpUcf-Q&s=66nUnJUf-sK8rlQDHFugtb1q27lTvOdsm_6C61ifZSM&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=eNYrr5T4YMj8KPepXAE5fV644gwPkXJumvSKDpUcf-Q&s=XxiqNxBgHmA3zUDbTjfK-hUMfd0SLM0PfEcFug4s5os&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 -
> >
> > Hmm, can't seem to reproduce it with this (& I don't mind just the full command line that crashes clang - rather than having to take it from clang to opt, etc, if you have that) - any ideas? (I'm trying to reproduce at r245521, FWIW)
> 
> This is the setup I used for delta/creduce:
> 
> $ cat test.sh
> set -e
> clang-3.8 -cc1 -triple arm64-apple-ios -emit-llvm -main-file-name action.c -gdwarf-2 -O2 -x c action.i -o action.ll &>/dev/null
> FileCheck test.sh <action.ll
> echo SUCCESS
> # CHECK: tail call i32 @pid_for_task({{.*\)[^,]+$}}
> 
> Ah, sorry, I see - you were checking for the IR, rather than the crash. Fair (I was expecting a crash - but that would've require more (unnecessary for the issue at hand) code). I'll work with that :)
>  
> 
> $ cat action.i
> 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);
> }
> 
> I noticed that when running the test through opt running through opt -gvn alone did not reproduce the error, but running through opt -O2 -gvn did, although none of the passes running before gvn (or after) changed the IR, so it is possible that there is nondeterminism involved.
> I also tried to add an assertion into GVN and running bugpoint on the IR, but it failed to reduce the testcase any further.
> 
> -- adrian
> >
> >
> > -- 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=eNYrr5T4YMj8KPepXAE5fV644gwPkXJumvSKDpUcf-Q&s=jVbD8YlqXdqvVo6_qrkhVGj5KxY14cJx0_bYbxCPb7U&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)
> >>
> >>
> >> _______________________________________________
> >> llvm-commits mailing list
> >> llvm-commits at lists.llvm.org <mailto:llvm-commits at lists.llvm.org>
> >> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-commits <https://urldefense.proofpoint.com/v2/url?u=http-3A__lists.llvm.org_cgi-2Dbin_mailman_listinfo_llvm-2Dcommits&d=BQMFaQ&c=eEvniauFctOgLOKGJOplqw&r=cTx6f1tAfqPeajYunFWp7_8ot79RnHyNteqzig4fXmA&m=eNYrr5T4YMj8KPepXAE5fV644gwPkXJumvSKDpUcf-Q&s=ZbGHxmAez5vG4uU29URX7PVFjeU0D0symCSkjs8YPQs&e=>
> 
> 
> 

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