[llvm] Handle missing debug info when updating sample counts

[mtrofin]

Summary

Clear profiling metadata when trying to update it, and debug info is missing.

[davidxl]

llvm/test/Transforms/SampleProfile/entry_counts_missing_dbginfo.ll

4

Can you explain exactly what happens that triggers the div by zero? when bar is inlined?

[mtrofin]

• Comments, tests pass.

[davidxl]

llvm/lib/Transforms/IPO/SampleProfile.cpp

1667

why 'WantAccurateProfile' guard?

llvm/test/Transforms/SampleProfile/entry_counts_missing_dbginfo.ll

8

Needs clarification. When the function is not inlined, why is there need to update its profile? Can you point to the compiler source that does this?

[mtrofin]

• Comments, tests pass.

[mtrofin]

llvm/lib/Transforms/IPO/SampleProfile.cpp

1667

To avoid breaking existing tests & code. When we don't want accurate profiles, we set the entry count to -1 ("invalid"), which is recognized by existing code and handled appropriately.

However, come to think of it, that would still leave the prof data valid within the function. For consistency, we could perhaps set those to -1 as well.

I would prefer changing the current behavior in the non-precise case in a separate CL - thoughts?

llvm/test/Transforms/SampleProfile/entry_counts_missing_dbginfo.ll

8

Added more detail.

[davidxl]

llvm/test/Transforms/SampleProfile/entry_counts_missing_dbginfo.ll

8

what I meant is the what the callstack is when div by 0 happens. In particular, why the update occurs when there is no inline (as mentioned in the comment).

[davidxl]

llvm/lib/Transforms/Utils/InlineFunction.cpp

1472

See line 1468 above -- the priorEntryCount can be zero which will trigger assertion at 1473. line 1468 can be executed before becaue updateProfileCallee can be invoked in two different contexts:

1. during inline transformation
2. after sample loading for the function.

1. can happen before 2).

In other words, the div by zero can still happen with when debug information is avaiable.

llvm/lib/Transforms/IPO/SampleProfile.cpp

if (LocalChanged) {
       break;
     }
   }
 
   // Accumulate not inlined callsite information into notInlinedSamples
   for (const auto &Pair : localNotInlinedCallSites) {
     Instruction *I = Pair.getFirst();
     Function *Callee = CallSite(I).getCalledFunction();
-    if (!Callee || Callee->isDeclaration())
+    if (!Callee || Callee->isDeclaration() || getFunctionLoc(*Callee) == 0)
       continue;
     const FunctionSamples *FS = Pair.getSecond();
     auto pair =
         notInlinedCallInfo.try_emplace(Callee, NotInlinedProfileInfo{0});
     pair.first->second.entryCount += FS->getEntrySamples();
   }
   return Changed;
 }
bool SampleProfileLoaderLegacyPass::runOnModule(Module &M) {
   ACT = &getAnalysis<AssumptionCacheTracker>();
   TTIWP = &getAnalysis<TargetTransformInfoWrapperPass>();
   ProfileSummaryInfo *PSI =
       &getAnalysis<ProfileSummaryInfoWrapperPass>().getPSI();
   return SampleLoader.runOnModule(M, nullptr, PSI);
 }
 
 bool SampleProfileLoader::runOnFunction(Function &F, ModuleAnalysisManager *AM) {
-  
   DILocation2SampleMap.clear();
   // By default the entry count is initialized to -1, which will be treated
   // conservatively by getEntryCount as the same as unknown (None). This is
   // to avoid newly added code to be treated as cold. If we have samples
   // this will be overwritten in emitAnnotations.
   // If ProfileSampleAccurate is true or F has profile-sample-accurate
   // attribute, initialize the entry count to 0 so callsites or functions
   // unsampled will be treated as cold.
-  uint64_t initialEntryCount =
-      (ProfileSampleAccurate || F.hasFnAttribute("profile-sample-accurate"))
-          ? 0
-          : -1;
+  bool WantAccurateProfile =
+      ProfileSampleAccurate || F.hasFnAttribute("profile-sample-accurate");
+  uint64_t initialEntryCount = WantAccurateProfile ? 0 : -1;
   F.setEntryCount(ProfileCount(initialEntryCount, Function::PCT_Real));
+
+  if (WantAccurateProfile && getFunctionLoc(F) == 0) {
+    // We won't be able to match samples. Reset all !prof metadata.
+    for (auto &BB : F) {
+      for (auto &I : BB) {
+        I.setMetadata(LLVMContext::MD_prof, nullptr);
+      }
+    }
+  }
+
   std::unique_ptr<OptimizationRemarkEmitter> OwnedORE;
   if (AM) {
     auto &FAM =
         AM->getResult<FunctionAnalysisManagerModuleProxy>(*F.getParent())
             .getManager();
     ORE = &FAM.getResult<OptimizationRemarkEmitterAnalysis>(F);
   } else {
     OwnedORE = make_unique<OptimizationRemarkEmitter>(&F);

llvm/lib/Transforms/Utils/InlineFunction.cpp

void llvm::updateProfileCallee(
 
   // Since CallSiteCount is an estimate, it could exceed the original callee
   // count and has to be set to 0 so guard against underflow.
   if (entryDelta < 0 && static_cast<uint64_t>(-entryDelta) > priorEntryCount)
     newEntryCount = 0;
   else
     newEntryCount = priorEntryCount + entryDelta;
 
   Callee->setEntryCount(newEntryCount);
-
+  assert(priorEntryCount > 0 && "Cannot update prof weights when prior entry "
+                                "count is 0 - it would result in a div by 0.");
   // During inlining ?
   if (VMap) {
     uint64_t cloneEntryCount = priorEntryCount - newEntryCount;
     for (auto const &Entry : *VMap)
       if (isa<CallInst>(Entry.first))
         if (auto *CI = dyn_cast_or_null<CallInst>(Entry.second))
           CI->updateProfWeight(cloneEntryCount, priorEntryCount);
   }

llvm/test/Transforms/SampleProfile/entry_counts_missing_dbginfo.ll

+; RUN: opt < %s -sample-profile -sample-profile-file=%S/Inputs/entry_counts_cold.prof -S -profile-sample-accurate | FileCheck %s
+; ModuleID = 'temp.bc'
+; This is a test similar to entry_counts_cold.ll. The key differences are:
+; - we want profile-sample-accurate. Normally, that would trigger resetting function entry counts to 0, and then update
+; them based on the sample profile. We also update, subsequently, the profile counts of calls within this function.
+; - we don't have debug info for the function. This means we can't match sample counts in the profile to locations in this function.
+; When this function is not inlined, but it was in the sampled program, we'll attempt to update its profile info, as well as the
+; profile weights of calls within the function. Updating profile weights (CallInst::updateProfWeight) divides the new entry count
+; by the current one, which was reset to 0.
+; We're using @bar and the call to @baz.
+source_filename = "temp.c"
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.14.0"
+
+; Function Attrs: nounwind ssp uwtable
+; CHECK: define i32 @top({{.*}} !prof [[TOP:![0-9]+]]
+define i32 @top(i32* %p) #0 !dbg !8 {
+entry:
+  %p.addr = alloca i32*, align 8
+  store i32* %p, i32** %p.addr, align 8, !tbaa !15
+  call void @llvm.dbg.declare(metadata i32** %p.addr, metadata !14, metadata !DIExpression()), !dbg !19
+  %0 = load i32*, i32** %p.addr, align 8, !dbg !20, !tbaa !15
+  %call = call i32 @foo(i32* %0), !dbg !21
+; foo is inlined
+; CHECK-NOT: call i32 @foo
+; CHECK: call i32 @bar
+  %1 = load i32*, i32** %p.addr, align 8, !dbg !22, !tbaa !15
+  %2 = load i32, i32* %1, align 4, !dbg !24, !tbaa !25
+  %tobool = icmp ne i32 %2, 0, !dbg !24
+  br i1 %tobool, label %if.then, label %if.end, !dbg !27
+
+if.then:                                          ; preds = %entry
+  %3 = load i32*, i32** %p.addr, align 8, !dbg !28, !tbaa !15
+; bar is not inlined
+; CHECK: call i32 @bar
+  %call1 = call i32 @bar(i32* %3), !dbg !29
+  br label %if.end, !dbg !29
+
+if.end:                                           ; preds = %if.then, %entry
+  ret i32 0, !dbg !30
+}
+
+; Function Attrs: nounwind readnone speculatable
+declare void @llvm.dbg.declare(metadata, metadata, metadata) #1
+
+; Function Attrs: nounwind ssp uwtable
+; CHECK: define i32 @foo({{.*}} !prof [[FOO:![0-9]+]]
+define i32 @foo(i32* %p) #0 !dbg !31 {
+entry:
+  %p.addr = alloca i32*, align 8
+  %a = alloca i32, align 4
+  store i32* %p, i32** %p.addr, align 8, !tbaa !15
+  call void @llvm.dbg.declare(metadata i32** %p.addr, metadata !33, metadata !DIExpression()), !dbg !35
+  %0 = bitcast i32* %a to i8*, !dbg !36
+  call void @llvm.lifetime.start.p0i8(i64 4, i8* %0) #4, !dbg !36
+  call void @llvm.dbg.declare(metadata i32* %a, metadata !34, metadata !DIExpression()), !dbg !37
+  %1 = load i32*, i32** %p.addr, align 8, !dbg !38, !tbaa !15
+  %arrayidx = getelementptr inbounds i32, i32* %1, i64 3, !dbg !38
+  %2 = load i32, i32* %arrayidx, align 4, !dbg !38, !tbaa !25
+  %3 = load i32*, i32** %p.addr, align 8, !dbg !39, !tbaa !15
+  %arrayidx1 = getelementptr inbounds i32, i32* %3, i64 2, !dbg !39
+  %4 = load i32, i32* %arrayidx1, align 4, !dbg !40, !tbaa !25
+  %add = add nsw i32 %4, %2, !dbg !40
+  store i32 %add, i32* %arrayidx1, align 4, !dbg !40, !tbaa !25
+  %5 = load i32*, i32** %p.addr, align 8, !dbg !41, !tbaa !15
+  %call = call i32 @bar(i32* %5), !dbg !42
+  store i32 %call, i32* %a, align 4, !dbg !43, !tbaa !25
+  %6 = load i32, i32* %a, align 4, !dbg !44, !tbaa !25
+  %add2 = add nsw i32 %6, 1, !dbg !45
+  %7 = bitcast i32* %a to i8*, !dbg !46
+  call void @llvm.lifetime.end.p0i8(i64 4, i8* %7) #4, !dbg !46
+  ret i32 %add2, !dbg !47
+}
+
+; Function Attrs: nounwind ssp uwtable
+; CHECK: define i32 @bar(i32* %p) #0 !prof [[BAR:![0-9]+]] {
+define i32 @bar(i32* %p) #0 {
+entry:
+  %p.addr = alloca i32*, align 8
+  store i32* %p, i32** %p.addr, align 8, !tbaa !15
+  call void @llvm.dbg.declare(metadata i32** %p.addr, metadata !50, metadata !DIExpression()), !dbg !51
+  ; CHECK: call void (...) @baz(), !dbg !{{[0-9]+}}{{$}}
+  call void (...) @baz(), !dbg !52, !prof !100
+  %0 = load i32*, i32** %p.addr, align 8, !dbg !53, !tbaa !15
+  %arrayidx = getelementptr inbounds i32, i32* %0, i64 2, !dbg !53
+  %1 = load i32, i32* %arrayidx, align 4, !dbg !53, !tbaa !25
+  %2 = load i32*, i32** %p.addr, align 8, !dbg !54, !tbaa !15
+  %arrayidx1 = getelementptr inbounds i32, i32* %2, i64 1, !dbg !54
+  %3 = load i32, i32* %arrayidx1, align 4, !dbg !55, !tbaa !25
+  %add = add nsw i32 %3, %1, !dbg !55
+  store i32 %add, i32* %arrayidx1, align 4, !dbg !55, !tbaa !25
+  %4 = load i32*, i32** %p.addr, align 8, !dbg !56, !tbaa !15
+  %arrayidx2 = getelementptr inbounds i32, i32* %4, i64 3, !dbg !56
+  %5 = load i32, i32* %arrayidx2, align 4, !dbg !56, !tbaa !25
+  ret i32 %5, !dbg !57
+}
+
+; Function Attrs: argmemonly nounwind
+declare void @llvm.lifetime.start.p0i8(i64, i8* nocapture) #2
+
+; Function Attrs: argmemonly nounwind
+declare void @llvm.lifetime.end.p0i8(i64, i8* nocapture) #2
+
+declare void @baz(...) #3
+
+attributes #0 = { nounwind ssp uwtable "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "min-legal-vector-width"="0" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="penryn" "target-features"="+cx16,+fxsr,+mmx,+sahf,+sse,+sse2,+sse3,+sse4.1,+ssse3,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #1 = { nounwind readnone speculatable }
+attributes #2 = { argmemonly nounwind }
+attributes #3 = { "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="penryn" "target-features"="+cx16,+fxsr,+mmx,+sahf,+sse,+sse2,+sse3,+sse4.1,+ssse3,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #4 = { nounwind }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5, !6}
+!llvm.ident = !{!7}
+
+; CHECK: [[TOP]] = !{!"function_entry_count", i64 101}
+; CHECK: [[FOO]] = !{!"function_entry_count", i64 151}
+; CHECK: [[BAR]] = !{!"function_entry_count", i64 0}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 8.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, nameTableKind: GNU)
+!1 = !DIFile(filename: "temp.c", directory: "llvm/test/Transforms/SampleProfile")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!6 = !{i32 7, !"PIC Level", i32 2}
+!7 = !{!"clang version 8.0.0"}
+!8 = distinct !DISubprogram(name: "top", scope: !1, file: !1, line: 5, type: !9, scopeLine: 5, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !13)
+!9 = !DISubroutineType(types: !10)
+!10 = !{!11, !12}
+!11 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!12 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !11, size: 64)
+!13 = !{!14}
+!14 = !DILocalVariable(name: "p", arg: 1, scope: !8, file: !1, line: 5, type: !12)
+!15 = !{!16, !16, i64 0}
+!16 = !{!"any pointer", !17, i64 0}
+!17 = !{!"omnipotent char", !18, i64 0}
+!18 = !{!"Simple C/C++ TBAA"}
+!19 = !DILocation(line: 5, column: 14, scope: !8)
+!20 = !DILocation(line: 6, column: 7, scope: !8)
+!21 = !DILocation(line: 6, column: 3, scope: !8)
+!22 = !DILocation(line: 7, column: 8, scope: !23)
+!23 = distinct !DILexicalBlock(scope: !8, file: !1, line: 7, column: 7)
+!24 = !DILocation(line: 7, column: 7, scope: !23)
+!25 = !{!26, !26, i64 0}
+!26 = !{!"int", !17, i64 0}
+!27 = !DILocation(line: 7, column: 7, scope: !8)
+!28 = !DILocation(line: 8, column: 9, scope: !23)
+!29 = !DILocation(line: 8, column: 5, scope: !23)
+!30 = !DILocation(line: 9, column: 3, scope: !8)
+!31 = distinct !DISubprogram(name: "foo", scope: !1, file: !1, line: 12, type: !9, scopeLine: 12, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !32)
+!32 = !{!33, !34}
+!33 = !DILocalVariable(name: "p", arg: 1, scope: !31, file: !1, line: 12, type: !12)
+!34 = !DILocalVariable(name: "a", scope: !31, file: !1, line: 13, type: !11)
+!35 = !DILocation(line: 12, column: 14, scope: !31)
+!36 = !DILocation(line: 13, column: 3, scope: !31)
+!37 = !DILocation(line: 13, column: 7, scope: !31)
+!38 = !DILocation(line: 14, column: 11, scope: !31)
+!39 = !DILocation(line: 14, column: 3, scope: !31)
+!40 = !DILocation(line: 14, column: 8, scope: !31)
+!41 = !DILocation(line: 15, column: 11, scope: !31)
+!42 = !DILocation(line: 15, column: 7, scope: !31)
+!43 = !DILocation(line: 15, column: 5, scope: !31)
+!44 = !DILocation(line: 16, column: 10, scope: !31)
+!45 = !DILocation(line: 16, column: 11, scope: !31)
+!46 = !DILocation(line: 17, column: 1, scope: !31)
+!47 = !DILocation(line: 16, column: 3, scope: !31)
+!48 = distinct !DISubprogram(name: "bar", scope: !1, file: !1, line: 19, type: !9, scopeLine: 19, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !49)
+!49 = !{!50}
+!50 = !DILocalVariable(name: "p", arg: 1, scope: !48, file: !1, line: 19, type: !12)
+!51 = !DILocation(line: 19, column: 15, scope: !48)
+!52 = !DILocation(line: 20, column: 3, scope: !48)
+!53 = !DILocation(line: 21, column: 11, scope: !48)
+!54 = !DILocation(line: 21, column: 3, scope: !48)
+!55 = !DILocation(line: 21, column: 8, scope: !48)
+!56 = !DILocation(line: 22, column: 10, scope: !48)
+!57 = !DILocation(line: 22, column: 3, scope: !48)
+!100 = !{!"branch_weights", i32 5, i32 10}