[KeyInstr] Fully support mixed key/non-key inlining modes #144103
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…ission A non-key-instructions function inlined into a key-instructions function uses non-key-instructions is_stmt placement (without `findForceIsStmtInstrs`). A key-instructions function inlined into a non-key-instructions function currently results in falling back to non-key-instructions for the inlined scope too. Both of these consessions (not using `findForceIsStmtInstrs` in the 1st case, and not using Key Instructions for the inlined scope in the 2nd) are for performance reasons; to do the right thing we'd need to run both `findForceIsStmtInstrs` and `computeKeyInstructions` - in case that's controversial I've got a seperate PR for that. <link to PR>
<link to cost>
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@llvm/pr-subscribers-debuginfo Author: Orlando Cazalet-Hyams (OCHyams) ChangesPatch 3/4 adding bitcode support, though the final patch doesn't depend on this one. Ignore the 1st commit in this PR (I'll rebase once the parent commit is merged). See <TODO: PR link>. There's a cost to doing the right thing here, these numbers are for non-key-instructions builds: Full diff: https://github.com/llvm/llvm-project/pull/144103.diff 2 Files Affected:
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
index 0edfca78b0886..44fa223a35635 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -169,8 +169,10 @@ static cl::opt<DwarfDebug::MinimizeAddrInV5> MinimizeAddrInV5Option(
"Stuff")),
cl::init(DwarfDebug::MinimizeAddrInV5::Default));
-static cl::opt<bool> KeyInstructionsAreStmts("dwarf-use-key-instructions",
- cl::Hidden, cl::init(false));
+/// Set to false to ignore Key Instructions metadata.
+static cl::opt<bool> KeyInstructionsAreStmts(
+ "dwarf-use-key-instructions", cl::Hidden, cl::init(true),
+ cl::desc("Set to false to ignore Key Instructions metadata"));
static constexpr unsigned ULEB128PadSize = 4;
@@ -2077,8 +2079,16 @@ void DwarfDebug::beginInstruction(const MachineInstr *MI) {
unsigned LastAsmLine =
Asm->OutStreamer->getContext().getCurrentDwarfLoc().getLine();
+ // Not-Key-Instructions functions inlined into Key Instructions functions
+ // should use default is_stmt handling. Key instructions functions
+ // inlined into not-key-instructions functions should use Key Instructions
+ // is_stmt handling.
+ bool ScopeUsesKeyInstructions =
+ KeyInstructionsAreStmts && DL &&
+ DL->getScope()->getSubprogram()->getKeyInstructionsEnabled();
+
bool IsKey = false;
- if (KeyInstructionsAreStmts && DL && DL.getLine())
+ if (ScopeUsesKeyInstructions && DL && DL.getLine())
IsKey = KeyInstructions.contains(MI);
if (!DL && MI == PrologEndLoc) {
@@ -2158,7 +2168,7 @@ void DwarfDebug::beginInstruction(const MachineInstr *MI) {
PrologEndLoc = nullptr;
}
- if (KeyInstructionsAreStmts) {
+ if (ScopeUsesKeyInstructions) {
if (IsKey)
Flags |= DWARF2_FLAG_IS_STMT;
} else {
@@ -2651,10 +2661,12 @@ void DwarfDebug::beginFunctionImpl(const MachineFunction *MF) {
PrologEndLoc = emitInitialLocDirective(
*MF, Asm->OutStreamer->getContext().getDwarfCompileUnitID());
+ // Run both `findForceIsStmtInstrs` and `computeKeyInstructions` because
+ // not-key-instructions functions may be inlined into key-instructions
+ // functions and vice versa.
if (KeyInstructionsAreStmts)
computeKeyInstructions(MF);
- else
- findForceIsStmtInstrs(MF);
+ findForceIsStmtInstrs(MF);
}
unsigned
diff --git a/llvm/test/DebugInfo/KeyInstructions/X86/dwarf-inline-modes.mir b/llvm/test/DebugInfo/KeyInstructions/X86/dwarf-inline-modes.mir
new file mode 100644
index 0000000000000..39fb4126332e5
--- /dev/null
+++ b/llvm/test/DebugInfo/KeyInstructions/X86/dwarf-inline-modes.mir
@@ -0,0 +1,92 @@
+# RUN: llc %s --start-after=livedebugvalues --dwarf-use-key-instructions --filetype=obj -o - \
+# RUN: | llvm-objdump -d - --no-show-raw-insn \
+# RUN: | FileCheck %s --check-prefix=OBJ
+
+# RUN: llc %s --start-after=livedebugvalues --dwarf-use-key-instructions --filetype=obj -o - \
+# RUN: | llvm-dwarfdump - --debug-line \
+# RUN: | FileCheck %s --check-prefix=DBG
+
+
+
+--- |
+ target triple = "x86_64-unknown-linux-gnu"
+
+ define hidden noundef i32 @key() local_unnamed_addr !dbg !5 {
+ entry:
+ ret i32 0
+ }
+
+ define hidden noundef i32 @not_key() local_unnamed_addr !dbg !9 {
+ entry:
+ ret i32 0
+ }
+
+ !llvm.dbg.cu = !{!0}
+ !llvm.module.flags = !{!2, !3}
+ !llvm.ident = !{!4}
+
+ !0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_17, file: !1, producer: "clang version 21.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: LineTablesOnly, splitDebugInlining: false, nameTableKind: None)
+ !1 = !DIFile(filename: "test.cpp", directory: "/")
+ !2 = !{i32 7, !"Dwarf Version", i32 5}
+ !3 = !{i32 2, !"Debug Info Version", i32 3}
+ !4 = !{!"clang version 21.0.0"}
+ !5 = distinct !DISubprogram(name: "key", scope: !1, file: !1, line: 1, type: !6, scopeLine: 1, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, keyInstructions: true)
+ !6 = !DISubroutineType(types: !7)
+ !7 = !{}
+ !9 = distinct !DISubprogram(name: "not_key", scope: !1, file: !1, line: 1, type: !6, scopeLine: 1, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, keyInstructions: false)
+ !10 = distinct !DILocation(line: 5, scope: !5)
+ !11 = distinct !DILocation(line: 9, scope: !9)
+...
+---
+name: key
+alignment: 16
+body: |
+ bb.0.entry:
+
+ ; OBJ: 0000000000000000 <key>:
+ ; OBJ-NEXT: 0: movl $0x1, %eax
+ ; OBJ-NEXT: 5: movl $0x2, %eax
+ ; OBJ-NEXT: a: movl $0x3, %eax
+ ; OBJ-NEXT: f: movl $0x4, %eax
+ ; OBJ-NEXT: 14: movl $0x5, %eax
+ ; OBJ-NEXT: 19: retq
+ ;
+ ; DBG: Address Line Column File ISA Discriminator OpIndex Flags
+ ; DBG-NEXT: ------------------ ------ ------ ------ --- ------------- ------- -------------
+ ; DBG-NEXT: 0x0000000000000000 1 0 0 0 0 0 is_stmt prologue_end
+ ; DBG-NEXT: 0x0000000000000005 2 0 0 0 0 0 is_stmt
+ ; DBG-NEXT: 0x000000000000000a 2 0 0 0 0 0
+ ; DBG-NEXT: 0x000000000000000f 3 0 0 0 0 0 is_stmt
+ ; DBG-NEXT: 0x0000000000000014 3 0 0 0 0 0
+ ;
+ $eax = MOV32ri 1, debug-location !DILocation(line: 1, scope: !5) ; is_stmt (prologue_end)
+ $eax = MOV32ri 2, debug-location !DILocation(line: 2, scope: !5, atomGroup: 1, atomRank: 1) ; is_stmt (key)
+ $eax = MOV32ri 3, debug-location !DILocation(line: 2, scope: !9, inlinedAt: !10)
+ $eax = MOV32ri 4, debug-location !DILocation(line: 3, scope: !9, inlinedAt: !10) ; is_stmt (not_key)
+ $eax = MOV32ri 5, debug-location !DILocation(line: 3, scope: !5, atomGroup: 1, atomRank: 2) ; is_stmt (key)
+ RET64 $eax, debug-location !DILocation(line: 3, scope: !5, atomGroup: 1, atomRank: 1)
+...
+---
+name: not_key
+alignment: 16
+body: |
+ bb.0.entry:
+
+ ; OBJ: 0000000000000020 <not_key>:
+ ; OBJ-NEXT: 20: movl $0x1, %eax
+ ; OBJ-NEXT: 25: movl $0x2, %eax
+ ; OBJ-NEXT: 2a: movl $0x3, %eax
+ ; OBJ-NEXT: 2f: retq
+ ;
+ ; Address Line Column File ISA Discriminator OpIndex Flags
+ ; ------------------ ------ ------ ------ --- ------------- ------- -------------
+ ; DBG-NEXT: 0x0000000000000020 1 0 0 0 0 0 is_stmt prologue_end
+ ; DBG-NEXT: 0x0000000000000025 2 0 0 0 0 0
+ ; DBG-NEXT: 0x000000000000002a 3 0 0 0 0 0 is_stmt
+ ; DBG-NEXT: 0x000000000000002f 3 0 0 0 0 0
+ ;
+ $eax = MOV32ri 1, debug-location !DILocation(line: 1, scope: !9) ; is_stmt (prologue_end)
+ $eax = MOV32ri 2, debug-location !DILocation(line: 2, scope: !5, inlinedAt: !11, atomGroup: 1, atomRank: 2)
+ $eax = MOV32ri 3, debug-location !DILocation(line: 3, scope: !5, inlinedAt: !11, atomGroup: 1, atomRank: 1) ; is_stmt (key)
+ RET64 $eax, debug-location !DILocation(line: 3, scope: !9)
+...
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This was referenced Jun 13, 2025
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Patch 3/4 adding bitcode support, though the final patch doesn't depend on this one. Ignore the 1st commit in this PR (I'll rebase once the parent commit is merged).
See summary in #144104 which this patch depends on. There's a cost to doing the right thing here, these numbers are for non-key-instructions builds:
https://llvm-compile-time-tracker.com/compare.php?from=bbdb9a446a87de0e3fc45a4016ceec41edb5c51b&to=25537e1b9cd4a50dd1b8575b5ad3ba250b7c0c12&stat=instructions%3Au