[Assignment Tracking] Don't run declare-to-assign on functions marked optnone

[Orlando]

Summary

Assignment tracking doesn't add value when optimisations are disabled - don't apply it to functions marked optnone.

[jryans]

Seems straightforward, thanks! 🙂

[Orlando]

Thanks! N.B. I added an --implicit-check-not to the test.

llvm/lib/IR/DebugInfo.cpp

for (Instruction &I : *BBI) {
         (void)Assign;
         LLVM_DEBUG(errs() << " > INSERT: " << *Assign << "\n");
       }
     }
   }
 }
 
 bool AssignmentTrackingPass::runOnFunction(Function &F) {
+  // No value in assignment tracking without optimisations.
+  if (F.hasFnAttribute(Attribute::OptimizeNone))
+    return /*Changed*/ false;
+
   bool Changed = false;
   // Collect a map of {backing storage : dbg.declares} (currently "backing
   // storage" is limited to Allocas). We'll use this to find dbg.declares to
   // delete after running `trackAssignments`.
   DenseMap<const AllocaInst *, SmallPtrSet<DbgDeclareInst *, 2>> DbgDeclares;
   // Create another similar map of {storage : variables} that we'll pass to
   // trackAssignments.
   StorageToVarsMap Vars;

llvm/test/DebugInfo/Generic/assignment-tracking/optnone.ll

+; RUN: opt -S %s -o - --passes=declare-to-assign \
+; RUN: | FileCheck %s --implicit-check-not="call void @llvm.dbg"
+
+;; Assignment tracking doesn't add any value when optimisations are disabled.
+;; Check it doesn't get applied to functions marked optnone.
+
+; CHECK: @_Z3funv
+; CHECK: dbg.assign
+
+; CHECK: @_Z3funv2
+; CHECK: dbg.declare
+
+define dso_local void @_Z3funv() local_unnamed_addr !dbg !16 {
+entry:
+  %a = alloca i32
+  call void @llvm.dbg.declare(metadata ptr %a, metadata !20, metadata !DIExpression()), !dbg !25
+  ret void
+}
+
+; Function Attrs: noinline optnone
+define dso_local void @_Z3funv2() local_unnamed_addr #1 !dbg !39 {
+entry:
+  %a = alloca i32
+  call void @llvm.dbg.declare(metadata ptr %a, metadata !41, metadata !DIExpression()), !dbg !44
+  ret void
+}
+
+attributes #1 = {noinline optnone}
+
+declare void @llvm.dbg.declare(metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!2}
+!llvm.module.flags = !{!8, !9, !10, !11, !12, !13}
+!llvm.ident = !{!15}
+
+!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+!1 = distinct !DIGlobalVariable(name: "G", scope: !2, file: !3, line: 1, type: !7, isLocal: false, isDefinition: true)
+!2 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !3, producer: "clang version 17.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, globals: !4, splitDebugInlining: false, nameTableKind: None)
+!3 = !DIFile(filename: "test.cpp", directory: "/")
+!4 = !{!0, !5}
+!5 = !DIGlobalVariableExpression(var: !6, expr: !DIExpression())
+!6 = distinct !DIGlobalVariable(name: "F", scope: !2, file: !3, line: 1, type: !7, isLocal: false, isDefinition: true)
+!7 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!8 = !{i32 7, !"Dwarf Version", i32 5}
+!9 = !{i32 2, !"Debug Info Version", i32 3}
+!10 = !{i32 1, !"wchar_size", i32 4}
+!11 = !{i32 8, !"PIC Level", i32 2}
+!12 = !{i32 7, !"PIE Level", i32 2}
+!13 = !{i32 7, !"uwtable", i32 2}
+!15 = !{!"clang version 17.0.0"}
+!16 = distinct !DISubprogram(name: "fun", linkageName: "_Z3funv", scope: !3, file: !3, line: 3, type: !17, scopeLine: 3, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !2, retainedNodes: !19)
+!17 = !DISubroutineType(types: !18)
+!18 = !{null}
+!19 = !{!20}
+!20 = !DILocalVariable(name: "X", scope: !16, file: !3, line: 4, type: !21)
+!21 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!22 = !{}
+!25 = !DILocation(line: 0, scope: !16)
+!27 = distinct !DILexicalBlock(scope: !16, file: !3, line: 7, column: 7)
+!39 = distinct !DISubprogram(name: "fun2", linkageName: "_Z3funv2", scope: !3, file: !3, line: 3, type: !17, scopeLine: 3, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !2, retainedNodes: !40)
+!40 = !{!41}
+!41 = !DILocalVariable(name: "X", scope: !39, file: !3, line: 10, type: !21)
+!44 = !DILocation(line: 0, scope: !39)