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[DebugInfo][InstrRef] Avoid crash when values optimised out late in sdag 

It appears that we can emit all the instructions for a function, including
debug instructions, and then optimise some of the values out late.
Specifically, in the attached test case, an argument gets optimised out
after DBG_VALUE / DBG_INSTR_REFs are created. This confuses
MachineFunction::finalizeDebugInstrRefs, which expects to be able to find a
defining instruction, and crashes instead.

Fix this by identifying when there's no defining instruction, and
translating that instead into a DBG_VALUE $noreg.

Differential Revision: https://reviews.llvm.org/D114476
This commit is contained in:
Jeremy Morse 2021-11-24 10:20:03 +00:00
parent d9af9c2c5a
commit b8f68ad9cd
2 changed files with 51 additions and 5 deletions
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11
llvm/lib/CodeGen/MachineFunction.cpp
View File

@ -1170,9 +1170,10 @@ auto MachineFunction::salvageCopySSA(MachineInstr &MI)
void MachineFunction::finalizeDebugInstrRefs() {
auto *TII = getSubtarget().getInstrInfo();
auto MakeDbgValue = [&](MachineInstr &MI) {
auto MakeUndefDbgValue = [&](MachineInstr &MI) {
const MCInstrDesc &RefII = TII->get(TargetOpcode::DBG_VALUE);
MI.setDesc(RefII);
MI.getOperand(0).setReg(0);
MI.getOperand(1).ChangeToRegister(0, false);
};
@ -1187,15 +1188,15 @@ void MachineFunction::finalizeDebugInstrRefs() {
Register Reg = MI.getOperand(0).getReg();
// Some vregs can be deleted as redundant in the meantime. Mark those
// as DBG_VALUE $noreg.
if (Reg == 0) {
MakeDbgValue(MI);
// as DBG_VALUE $noreg. Additionally, some normal instructions are
// quickly deleted, leaving dangling references to vregs with no def.
if (Reg == 0 || !RegInfo->hasOneDef(Reg)) {
MakeUndefDbgValue(MI);
continue;
}
assert(Reg.isVirtual());
MachineInstr &DefMI = *RegInfo->def_instr_begin(Reg);
assert(RegInfo->hasOneDef(Reg));
// If we've found a copy-like instruction, follow it back to the
// instruction that defines the source value, see salvageCopySSA docs

45
llvm/test/DebugInfo/X86/instr-ref-sdag-empty-vreg.ll Normal file
View File

@ -0,0 +1,45 @@
; RUN: llc %s -o - -stop-before=finalize-isel \
; RUN: -experimental-debug-variable-locations \
; RUN: | FileCheck %s
;; The multiply by zero of %width below causes %width to become unused very late
;; in SelectionDAG. As a result, DBG_INSTR_REFs are produced that refer to a
;; vreg that is never defined, which risks a crash. Check that we don't crash,
;; and produce an empty variable location.
; CHECK: DBG_VALUE $noreg
target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-unknown"
%class.Color = type { i8 }
define hidden void @_Z14drawXZWideLineR4Vec3RK5Colorf(%class.Color* %color, float %width) local_unnamed_addr !dbg !7 {
cond.false.i:
br label %_ZN4Vec39normalizeEv.exit, !dbg !12
_ZN4Vec39normalizeEv.exit: ; preds = %cond.false.i
call void @llvm.dbg.value(metadata float %width, metadata !11, metadata !DIExpression()), !dbg !12
%mul.i = fmul float %width, 0.000000e+00, !dbg !12
ret void, !dbg !12
}
; Function Attrs: nofree nosync nounwind readnone speculatable willreturn
declare void @llvm.dbg.value(metadata, metadata, metadata)
!llvm.dbg.cu = !{!0}
!llvm.module.flags = !{!3, !4, !5, !6}
!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug)
!1 = !DIFile(filename: "foo.cpp", directory: ".")
!2 = !DIBasicType(name: "int", size: 8, encoding: DW_ATE_signed)
!3 = !{i32 2, !"Dwarf Version", i32 4}
!4 = !{i32 2, !"Debug Info Version", i32 3}
!5 = !{i32 1, !"wchar_size", i32 2}
!6 = !{i32 7, !"PIC Level", i32 2}
!7 = distinct !DISubprogram(name: "foo", linkageName: "foo", scope: !1, file: !1, line: 6, type: !8, scopeLine: 6, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !10)
!8 = !DISubroutineType(types: !9)
!9 = !{!2, !2}
!10 = !{!11}
!11 = !DILocalVariable(name: "baz", scope: !7, file: !1, line: 7, type: !2)
!12 = !DILocation(line: 10, scope: !7)