[llvm] Avoid div by 0 when updating profile weights.

[davidxl]

lgtm

llvm/lib/IR/Instructions.cpp

void CallInst::updateProfWeight(uint64_t S, uint64_t T) {
   if (ProfileData == nullptr)
     return;
 
   auto *ProfDataName = dyn_cast<MDString>(ProfileData->getOperand(0));
   if (!ProfDataName || (!ProfDataName->getString().equals("branch_weights") &&
                         !ProfDataName->getString().equals("VP")))
     return;
 
+  if (T == 0) {
+    LLVM_DEBUG(dbgs() << "Attempting to update profile weights will result in "
+                         "div by 0. Ignoring. Likely the function "
+                      << getParent()->getParent()->getName()
+                      << " has 0 entry count, and contains call instructions "
+                         "with non-zero prof info.");
+    return;
+  }
+
   MDBuilder MDB(getContext());
   SmallVector<Metadata *, 3> Vals;
   Vals.push_back(ProfileData->getOperand(0));
   APInt APS(128, S), APT(128, T);
   if (ProfDataName->getString().equals("branch_weights") &&
       ProfileData->getNumOperands() > 0) {
     // Using APInt::div may be expensive, but most cases should fit 64 bits.
     APInt Val(128, mdconst::dyn_extract<ConstantInt>(ProfileData->getOperand(1))

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 (SampleProfile::runOnFunction).
+; - 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 we attempt to update its profile info (at the end of SampleProfile::runOnModule - llvm::updateProfileCallee), we'll call
+; updateProfWeight with a 0 priorEntryCount, which will result in a division by 0.
+;
+; We're using @bar and the call to @baz.
+;
+; Currently, the test just ensures opt doesn't ICE
+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}
+
+!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}