[DWARF] Don't leak line numbers onto frame-setup instructions #161845
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@llvm/pr-subscribers-debuginfo Author: Orlando Cazalet-Hyams (OCHyams) ChangesFixes issue #157887 Full diff: https://github.com/llvm/llvm-project/pull/161845.diff 2 Files Affected:
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
index 05d3d18aa9557..073eb355491a7 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -2053,11 +2053,36 @@ void DwarfDebug::beginInstruction(const MachineInstr *MI) {
if (NoDebug)
return;
+ auto RecordLineZero = [&]() {
+ // Preserve the file and column numbers, if we can, to save space in
+ // the encoded line table.
+ // Do not update PrevInstLoc, it remembers the last non-0 line.
+ const MDNode *Scope = nullptr;
+ unsigned Column = 0;
+ if (PrevInstLoc) {
+ Scope = PrevInstLoc.getScope();
+ Column = PrevInstLoc.getCol();
+ }
+ recordSourceLine(/*Line=*/0, Column, Scope, /*Flags=*/0);
+ };
+
+ // When we emit a line-0 record, we don't update PrevInstLoc; so look at
+ // the last line number actually emitted, to see if it was line 0.
+ unsigned LastAsmLine =
+ Asm->OutStreamer->getContext().getCurrentDwarfLoc().getLine();
+
// Check if source location changes, but ignore DBG_VALUE and CFI locations.
// If the instruction is part of the function frame setup code, do not emit
// any line record, as there is no correspondence with any user code.
- if (MI->isMetaInstruction() || MI->getFlag(MachineInstr::FrameSetup))
+ if (MI->isMetaInstruction())
+ return;
+ if (MI->getFlag(MachineInstr::FrameSetup)) {
+ // Prevent a loc from the previous block leaking into frame setup instrs.
+ if (LastAsmLine && PrevInstBB && PrevInstBB != MI->getParent())
+ RecordLineZero();
return;
+ }
+
const DebugLoc &DL = MI->getDebugLoc();
unsigned Flags = 0;
@@ -2080,11 +2105,6 @@ void DwarfDebug::beginInstruction(const MachineInstr *MI) {
LocationString);
};
- // When we emit a line-0 record, we don't update PrevInstLoc; so look at
- // the last line number actually emitted, to see if it was line 0.
- unsigned LastAsmLine =
- Asm->OutStreamer->getContext().getCurrentDwarfLoc().getLine();
-
// There may be a mixture of scopes using and not using Key Instructions.
// Not-Key-Instructions functions inlined into Key Instructions functions
// should use not-key is_stmt handling. Key Instructions functions inlined
@@ -2150,18 +2170,8 @@ void DwarfDebug::beginInstruction(const MachineInstr *MI) {
// - Instruction is at the top of a block; we don't want to inherit the
// location from the physically previous (maybe unrelated) block.
if (UnknownLocations == Enable || PrevLabel ||
- (PrevInstBB && PrevInstBB != MI->getParent())) {
- // Preserve the file and column numbers, if we can, to save space in
- // the encoded line table.
- // Do not update PrevInstLoc, it remembers the last non-0 line.
- const MDNode *Scope = nullptr;
- unsigned Column = 0;
- if (PrevInstLoc) {
- Scope = PrevInstLoc.getScope();
- Column = PrevInstLoc.getCol();
- }
- recordSourceLine(/*Line=*/0, Column, Scope, /*Flags=*/0);
- }
+ (PrevInstBB && PrevInstBB != MI->getParent()))
+ RecordLineZero();
return;
}
diff --git a/llvm/test/DebugInfo/X86/shrink-wrap-frame-setup-no-loc.mir b/llvm/test/DebugInfo/X86/shrink-wrap-frame-setup-no-loc.mir
new file mode 100644
index 0000000000000..a6d9f96c4a592
--- /dev/null
+++ b/llvm/test/DebugInfo/X86/shrink-wrap-frame-setup-no-loc.mir
@@ -0,0 +1,139 @@
+# RUN: %llc_dwarf %s -o - -mtriple=x86_64-unknown-unknown | FileCheck %s
+
+## Check the line number from the ret above `.LBB0_1` doesn't leak onto the
+## frame setup instructions in the `.LBB0_1` block; `pushq %rax` should
+## explicitly get set to line zero.
+
+# CHECK: loop:
+# CHECK-NEXT: .Lfunc_begin0:
+# CHECK-NEXT: .cfi_startproc
+# CHECK-NEXT: # %bb.0:
+# CHECK-NEXT: .file 1 "/" "test.c"
+# CHECK-NEXT: .loc 1 5 16 prologue_end # test.c:5:16
+# CHECK-NEXT: testq %rax, %rax
+# CHECK-NEXT: je .LBB0_1
+# CHECK-NEXT: # %bb.2:
+# CHECK-NEXT: .loc 1 5 16 # test.c:5:16
+# CHECK-NEXT: retq
+# CHECK-NEXT: .LBB0_1:
+# -- Check the .loc below sets the current location to line 0.
+# CHECK-NEXT: .loc 1 0 16 is_stmt 0 # test.c:0:16
+# CHECK-NEXT: pushq %rax
+# CHECK-NEXT: .cfi_def_cfa_offset 16
+# CHECK-NEXT: addq $8, %rsp
+# CHECK-NEXT: .cfi_def_cfa_offset 8
+# CHECK-NEXT: .loc 1 5 16 is_stmt 1 # test.c:5:16
+# CHECK-NEXT: retq
+
+--- |
+ source_filename = "reduced.ll"
+ target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
+ target triple = "x86_64-unknown-unknown"
+
+ define void @loop(i64 %i) !dbg !4 {
+ entry:
+ %cmp.not = icmp eq i64 %i, 0, !dbg !7
+ br i1 %cmp.not, label %for.body, label %for.end
+
+ for.body: ; preds = %entry
+ %puts10 = tail call i32 null(ptr null)
+ %inc = add i64 0, 0
+ br label %for.end
+
+ for.end: ; preds = %for.body, %entry
+ ret void
+ }
+
+ !llvm.dbg.cu = !{!0}
+ !llvm.module.flags = !{!3}
+
+ !0 = distinct !DICompileUnit(language: DW_LANG_C11, file: !1, producer: "clang version 22.0.0git", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, globals: !2, splitDebugInlining: false, nameTableKind: None)
+ !1 = !DIFile(filename: "test.c", directory: "/")
+ !2 = !{}
+ !3 = !{i32 2, !"Debug Info Version", i32 3}
+ !4 = distinct !DISubprogram(name: "loop", scope: !1, file: !1, line: 4, type: !5, scopeLine: 4, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !2, keyInstructions: true)
+ !5 = !DISubroutineType(types: !6)
+ !6 = !{null}
+ !7 = !DILocation(line: 5, column: 16, scope: !8, atomGroup: 720, atomRank: 2)
+ !8 = distinct !DILexicalBlock(scope: !4, file: !1, line: 5, column: 9)
+...
+---
+name: loop
+alignment: 16
+exposesReturnsTwice: false
+legalized: false
+regBankSelected: false
+selected: false
+failedISel: false
+tracksRegLiveness: true
+hasWinCFI: false
+noPhis: false
+isSSA: true
+noVRegs: false
+hasFakeUses: false
+callsEHReturn: false
+callsUnwindInit: false
+hasEHContTarget: false
+hasEHScopes: false
+hasEHFunclets: false
+isOutlined: false
+debugInstrRef: false
+failsVerification: false
+tracksDebugUserValues: false
+registers:
+ - { id: 0, class: gr64, preferred-register: '', flags: [ ] }
+ - { id: 1, class: gr32, preferred-register: '', flags: [ ] }
+ - { id: 2, class: gr64, preferred-register: '', flags: [ ] }
+ - { id: 3, class: gr32, preferred-register: '', flags: [ ] }
+ - { id: 4, class: gr64, preferred-register: '', flags: [ ] }
+ - { id: 5, class: gr32, preferred-register: '', flags: [ ] }
+ - { id: 6, class: gr32, preferred-register: '', flags: [ ] }
+ - { id: 7, class: gr64, preferred-register: '', flags: [ ] }
+liveins: []
+frameInfo:
+ isFrameAddressTaken: false
+ isReturnAddressTaken: false
+ hasStackMap: false
+ hasPatchPoint: false
+ stackSize: 0
+ offsetAdjustment: 0
+ maxAlignment: 1
+ adjustsStack: false
+ hasCalls: true
+ stackProtector: ''
+ functionContext: ''
+ maxCallFrameSize: 4294967295
+ cvBytesOfCalleeSavedRegisters: 0
+ hasOpaqueSPAdjustment: false
+ hasVAStart: false
+ hasMustTailInVarArgFunc: false
+ hasTailCall: false
+ isCalleeSavedInfoValid: false
+ localFrameSize: 0
+fixedStack: []
+stack: []
+entry_values: []
+callSites: []
+debugValueSubstitutions: []
+constants: []
+machineFunctionInfo:
+ amxProgModel: None
+body: |
+ bb.0:
+ successors: %bb.1(0x30000000), %bb.2(0x50000000)
+ liveins: $rdi
+
+ %7:gr64 = IMPLICIT_DEF
+ TEST64rr undef %7, undef %7, implicit-def $eflags, debug-location !7
+ JCC_1 %bb.2, 5, implicit $eflags
+ JMP_1 %bb.1
+
+ bb.1:
+ successors: %bb.2(0x80000000)
+
+ ADJCALLSTACKDOWN64 0, 0, 0, implicit-def dead $rsp, implicit-def dead $eflags, implicit-def dead $ssp, implicit $rsp, implicit $ssp
+ ADJCALLSTACKUP64 0, 0, implicit-def dead $rsp, implicit-def dead $eflags, implicit-def dead $ssp, implicit $rsp, implicit $ssp
+
+ bb.2:
+ RET 0, debug-location !7
+...
|
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Code change LGTM. |
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Thanks!
No they were not. I can change this to use auto-generated checks if you think that's better for maintainability etc? |
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Ping :) |
jmorse
approved these changes
Oct 17, 2025
There was a problem hiding this comment.
LGTM; ideally the MIR would be generated with --simplify-mir.
I wonder whether the MIR is running the correct set of passes... we could start at a lower level where the push instructions exist and have framesetup flags. But on the other hand we cover the whole lowering-stack-changes-to-instructions process by having the test start this high, so the coverage is better. YMMV; I think it's probably fine as it is.
Learnt something new!
Starting after livedebugvalues (as an arbitrary late pass). How does this look? |
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Fixes issue #157887