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>
97 lines
3.7 KiB
LLVM
97 lines
3.7 KiB
LLVM
; RUN: llc %s -stop-after=finalize-isel -o - | FileCheck %s --implicit-check-not=DBG_VALUE
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;; Check stores to an address computed as a negative offset from an alloca are
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;; ignored by the assignment tracking analysis. For this example that should
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;; result in no DBG_VALUEs in the while.body.lr.ph branch.
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;;
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;; See llvm.org/PR62838 for more info.
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;;
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;; $ clang test.c -O1 -g
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;; $ cat tes.c
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;; void a(int *p);
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;; __attribute__((nodebug)) int b;
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;;
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;; int main() {
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;; int c[1];
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;; __attribute__((nodebug)) int d = -1;
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;;
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;; while (b) {
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;; c[0] = 0;
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;; c[d] = 0;
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;; }
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;; a(c);
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;; return 0;
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;; }
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; CHECK: bb.0.entry:
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; CHECK-NEXT: successors
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; CHECK-NEXT: {{^ *$}}
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; CHECK-NEXT: DBG_VALUE %stack.0.c, $noreg, ![[#]], !DIExpression(DW_OP_deref)
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; CHECK: bb.2.while.body:
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; CHECK-NEXT: successors
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; CHECK-NEXT: {{^ *$}}
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; CHECK-NEXT: DBG_VALUE 0, $noreg, ![[#]], !DIExpression()
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;; After the escaping call to @a, the memory location is reinstated.
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; CHECK: CALL64pcrel32 {{.*}}@a
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; CHECK: DBG_VALUE %stack.0.c, $noreg, ![[#]], !DIExpression(DW_OP_deref)
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target triple = "x86_64-unknown-linux-gnu"
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@b = dso_local local_unnamed_addr global i32 0, align 4
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define dso_local i32 @main() local_unnamed_addr #0 !dbg !10 {
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entry:
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%c = alloca [1 x i32], align 4, !DIAssignID !19
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call void @llvm.dbg.assign(metadata i1 undef, metadata !15, metadata !DIExpression(), metadata !19, metadata ptr %c, metadata !DIExpression()), !dbg !20
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%0 = load i32, ptr @b, align 4
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%tobool.not = icmp eq i32 %0, 0
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br i1 %tobool.not, label %while.end, label %while.body.lr.ph
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while.body.lr.ph: ; preds = %entry
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%arrayidx1 = getelementptr inbounds [1 x i32], ptr %c, i64 0, i64 -1
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store i32 0, ptr %arrayidx1, align 4
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br label %while.body
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while.body: ; preds = %while.body, %while.body.lr.ph
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call void @llvm.dbg.assign(metadata i32 0, metadata !15, metadata !DIExpression(), metadata !28, metadata ptr %c, metadata !DIExpression()), !dbg !20
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br label %while.body
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while.end: ; preds = %entry
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call void @a(ptr noundef nonnull %c)
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ret i32 0
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}
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declare !dbg !31 void @a(ptr noundef) local_unnamed_addr #2
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declare void @llvm.dbg.assign(metadata, metadata, metadata, metadata, metadata, metadata) #3
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!llvm.dbg.cu = !{!0}
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!llvm.module.flags = !{!2, !3, !8}
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!llvm.ident = !{!9}
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!0 = distinct !DICompileUnit(language: DW_LANG_C11, file: !1, producer: "clang version 17.0.0)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: None)
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!1 = !DIFile(filename: "test.c", directory: "/")
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!2 = !{i32 7, !"Dwarf Version", i32 5}
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!3 = !{i32 2, !"Debug Info Version", i32 3}
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!8 = !{i32 7, !"debug-info-assignment-tracking", i1 true}
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!9 = !{!"clang version 17.0.0"}
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!10 = distinct !DISubprogram(name: "main", scope: !1, file: !1, line: 4, type: !11, scopeLine: 4, flags: DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !14)
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!11 = !DISubroutineType(types: !12)
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!12 = !{!13}
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!13 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
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!14 = !{!15}
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!15 = !DILocalVariable(name: "c", scope: !10, file: !1, line: 5, type: !16)
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!16 = !DICompositeType(tag: DW_TAG_array_type, baseType: !13, size: 32, elements: !17)
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!17 = !{!18}
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!18 = !DISubrange(count: 1)
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!19 = distinct !DIAssignID()
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!20 = !DILocation(line: 0, scope: !10)
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!28 = distinct !DIAssignID()
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!31 = !DISubprogram(name: "a", scope: !1, file: !1, line: 1, type: !32, flags: DIFlagPrototyped, spFlags: DISPFlagOptimized, retainedNodes: !35)
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!32 = !DISubroutineType(types: !33)
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!33 = !{null, !34}
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!34 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !13, size: 64)
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!35 = !{}
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