839fd9177e
When a pointer to a tracked alloca is passed to a call that may write through it (e.g. foo(&x)), the callee can modify the variable's stack home. The assignment tracking analysis didn't account for this, which could cause the debugger to show stale values after such calls. Consider: ``` int x = 1; foo(&x); // might set x to 99 x = 2; // store deleted by DSE ``` Without this patch, the analysis still thinks the stack home holds assignment `!id1` after the call. When it later sees the `dbg_assign` for the deleted store, the mismatch causes it to fall back to the old debug value (1) , which is wrong. Fix this by detecting calls where a tracked `alloca` escapes as an argument and treating them the same way we already treat untagged stores, set both `StackHome` and `Debug` to NoneOrPhi (unknown assignment) and keep `LocKind` as Mem (the stack slot is still the right place to look). This causes a `DBG_VALUE` with `DW_OP_deref` to be emitted after the call, telling the debugger to read whatever is actually in memory. Pointer arguments with readonly, readnone, or byval attributes are skipped since the callee either cannot modify the original memory or receives a copy. Intrinsics are also skipped since their memory effects are already modeled individually (e.g. memset/memcpy as stores, lifetime markers as no-ops). --------- Co-authored-by: Shivam Kunwar <phyBrackets@users.noreply.github.com>
123 lines
5.8 KiB
LLVM
123 lines
5.8 KiB
LLVM
; RUN: llc %s -stop-after=finalize-isel -o - \
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; RUN: | FileCheck %s --implicit-check-not=DBG_
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;; $ cat test.cpp
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;; int d();
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;; void e();
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;; void es(int*);
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;; int *g;
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;; int f(int a, int b, int c) {
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;; do {
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;; /* stuff */
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;; c *= c;
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;; a = b;
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;; e();
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;; } while (d());
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;; es(&a);
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;; return a + c;
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;; }
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;; The variable of interest is `a`, which has a store that is hoisted out of the
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;; loop into the entry BB. Check the memory location is not used after the
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;; hoisted store until the assignment position within the loop.
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; CHECK-DAG: ![[A:[0-9]+]] = !DILocalVariable(name: "a",
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; CHECK: bb.0.entry:
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; CHECK: DBG_VALUE $edi, $noreg, ![[A]], !DIExpression()
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; CHECK: bb.1.do.body:
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; CHECK: DBG_VALUE %stack.0.a.addr, $noreg, ![[A]], !DIExpression(DW_OP_deref)
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;; After the escaping call to @_Z2esPi, the memory location is reinstated.
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; CHECK: CALL64pcrel32 {{.*}}@_Z2esPi
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; CHECK: DBG_VALUE %stack.0.a.addr, $noreg, ![[A]], !DIExpression(DW_OP_deref)
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target triple = "x86_64-unknown-linux-gnu"
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@g = dso_local local_unnamed_addr global ptr null, align 8, !dbg !0
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define dso_local noundef i32 @_Z1fiii(i32 noundef %a, i32 noundef %b, i32 noundef %c) local_unnamed_addr #0 !dbg !12 {
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entry:
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%a.addr = alloca i32, align 4, !DIAssignID !19
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call void @llvm.dbg.assign(metadata i1 undef, metadata !16, metadata !DIExpression(), metadata !19, metadata ptr %a.addr, metadata !DIExpression()), !dbg !20
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call void @llvm.dbg.assign(metadata i32 %a, metadata !16, metadata !DIExpression(), metadata !21, metadata ptr %a.addr, metadata !DIExpression()), !dbg !20
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store i32 %b, ptr %a.addr, align 4, !DIAssignID !28
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br label %do.body, !dbg !29
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do.body: ; preds = %do.body, %entry
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%c.addr.0 = phi i32 [ %c, %entry ], [ %mul, %do.body ]
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%mul = mul nsw i32 %c.addr.0, %c.addr.0, !dbg !30
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call void @llvm.dbg.assign(metadata i32 %b, metadata !16, metadata !DIExpression(), metadata !28, metadata ptr %a.addr, metadata !DIExpression()), !dbg !20
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tail call void @_Z1ev(), !dbg !33
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%call = tail call noundef i32 @_Z1dv(), !dbg !34
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%tobool.not = icmp eq i32 %call, 0, !dbg !34
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br i1 %tobool.not, label %do.end, label %do.body, !dbg !35, !llvm.loop !36
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do.end: ; preds = %do.body
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call void @_Z2esPi(ptr noundef nonnull %a.addr), !dbg !39
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%0 = load i32, ptr %a.addr, align 4, !dbg !40
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%add = add nsw i32 %0, %mul, !dbg !41
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ret i32 %add, !dbg !42
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}
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declare !dbg !43 dso_local void @_Z1ev() local_unnamed_addr #1
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declare !dbg !47 dso_local noundef i32 @_Z1dv() local_unnamed_addr #1
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declare !dbg !50 dso_local void @_Z2esPi(ptr noundef) local_unnamed_addr #1
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declare void @llvm.dbg.assign(metadata, metadata, metadata, metadata, metadata, metadata) #2
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declare void @llvm.dbg.value(metadata, metadata, metadata) #3
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!llvm.dbg.cu = !{!2}
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!llvm.module.flags = !{!7, !8, !9, !10, !1000}
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!llvm.ident = !{!11}
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!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
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!1 = distinct !DIGlobalVariable(name: "g", scope: !2, file: !3, line: 4, type: !5, isLocal: false, isDefinition: true)
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!2 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !3, producer: "clang version 14.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, globals: !4, splitDebugInlining: false, nameTableKind: None)
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!3 = !DIFile(filename: "test.cpp", directory: "/")
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!4 = !{!0}
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!5 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !6, size: 64)
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!6 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
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!7 = !{i32 7, !"Dwarf Version", i32 5}
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!8 = !{i32 2, !"Debug Info Version", i32 3}
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!9 = !{i32 1, !"wchar_size", i32 4}
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!10 = !{i32 7, !"uwtable", i32 1}
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!11 = !{!"clang version 14.0.0"}
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!12 = distinct !DISubprogram(name: "f", linkageName: "_Z1fiii", scope: !3, file: !3, line: 5, type: !13, scopeLine: 5, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !2, retainedNodes: !15)
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!13 = !DISubroutineType(types: !14)
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!14 = !{!6, !6, !6, !6}
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!15 = !{!16, !17, !18}
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!16 = !DILocalVariable(name: "a", arg: 1, scope: !12, file: !3, line: 5, type: !6)
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!17 = !DILocalVariable(name: "b", arg: 2, scope: !12, file: !3, line: 5, type: !6)
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!18 = !DILocalVariable(name: "c", arg: 3, scope: !12, file: !3, line: 5, type: !6)
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!19 = distinct !DIAssignID()
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!20 = !DILocation(line: 0, scope: !12)
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!21 = distinct !DIAssignID()
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!22 = distinct !DIAssignID()
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!23 = distinct !DIAssignID()
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!28 = distinct !DIAssignID()
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!29 = !DILocation(line: 6, column: 3, scope: !12)
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!30 = !DILocation(line: 8, column: 7, scope: !31)
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!31 = distinct !DILexicalBlock(scope: !12, file: !3, line: 6, column: 6)
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!32 = distinct !DIAssignID()
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!33 = !DILocation(line: 10, column: 5, scope: !31)
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!34 = !DILocation(line: 11, column: 12, scope: !12)
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!35 = !DILocation(line: 11, column: 3, scope: !31)
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!36 = distinct !{!36, !29, !37, !38}
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!37 = !DILocation(line: 11, column: 15, scope: !12)
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!38 = !{!"llvm.loop.mustprogress"}
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!39 = !DILocation(line: 12, column: 3, scope: !12)
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!40 = !DILocation(line: 13, column: 10, scope: !12)
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!41 = !DILocation(line: 13, column: 12, scope: !12)
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!42 = !DILocation(line: 13, column: 3, scope: !12)
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!43 = !DISubprogram(name: "e", linkageName: "_Z1ev", scope: !3, file: !3, line: 2, type: !44, flags: DIFlagPrototyped, spFlags: DISPFlagOptimized, retainedNodes: !46)
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!44 = !DISubroutineType(types: !45)
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!45 = !{null}
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!46 = !{}
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!47 = !DISubprogram(name: "d", linkageName: "_Z1dv", scope: !3, file: !3, line: 1, type: !48, flags: DIFlagPrototyped, spFlags: DISPFlagOptimized, retainedNodes: !46)
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!48 = !DISubroutineType(types: !49)
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!49 = !{!6}
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!50 = !DISubprogram(name: "es", linkageName: "_Z2esPi", scope: !3, file: !3, line: 3, type: !51, flags: DIFlagPrototyped, spFlags: DISPFlagOptimized, retainedNodes: !46)
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!51 = !DISubroutineType(types: !52)
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!52 = !{null, !5}
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!1000 = !{i32 7, !"debug-info-assignment-tracking", i1 true}
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