[PATCH] D117489: [SDAG] Don't move DBG_VALUE instructions after insertion point during scheduling

[Nikita Popov via Phabricator via llvm-commits]

nikic created this revision.
nikic added reviewers: fhahn, aprantl.
Herald added subscribers: pengfei, hiraditya, MatzeB.
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EmitSchedule() shouldn't be touching instructions after the provided insertion point. The change introduced in D83561 <https://reviews.llvm.org/D83561> performs a scan to the end of the block, and thus may move unrelated instructions. In particular, this ends up moving instructions that have been produced by FastISel and will later be deleted. Moving them means that more instructions than intended are removed.

Fix this by stopping the iteration when the insertion point is reached.


https://reviews.llvm.org/D117489

Files:
  llvm/lib/CodeGen/SelectionDAG/ScheduleDAGSDNodes.cpp
  llvm/test/CodeGen/X86/pr53243-tail-call-fastisel.ll


Index: llvm/test/CodeGen/X86/pr53243-tail-call-fastisel.ll
===================================================================
--- /dev/null
+++ llvm/test/CodeGen/X86/pr53243-tail-call-fastisel.ll
@@ -0,0 +1,50 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -O0 -fast-isel -mtriple=x86_64-- < %s | FileCheck %s
+
+define void @test() {
+; CHECK-LABEL: test:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    jmp set_state at PLT # TAILCALL
+  tail call void @set_state()
+  call void @llvm.dbg.value(metadata i64 0, metadata !12, metadata !DIExpression()), !dbg !27
+  ret void
+}
+
+declare void @set_state()
+
+; Function Attrs: nofree nosync nounwind readnone speculatable willreturn
+declare void @llvm.dbg.value(metadata, metadata, metadata) #0
+
+attributes #0 = { nofree nosync nounwind readnone speculatable willreturn }
+
+!llvm.module.flags = !{!0}
+!llvm.dbg.cu = !{!1}
+
+!0 = !{i32 2, !"Debug Info Version", i32 3}
+!1 = distinct !DICompileUnit(language: DW_LANG_Rust, file: !2, producer: "clang LLVM (rustc version 1.60.0-nightly (ec4bcaac4 2022-01-15))", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !3)
+!2 = !DIFile(filename: "src/lib.rs/@/bug.63e521cd-cgu.0", directory: "/tmp/rust-bug")
+!3 = !{!4}
+!4 = !DICompositeType(tag: DW_TAG_enumeration_type, name: "Option", scope: !6, file: !5, baseType: !8, size: 8, align: 8, flags: DIFlagEnumClass, elements: !9)
+!5 = !DIFile(filename: "<unknown>", directory: "")
+!6 = !DINamespace(name: "option", scope: !7)
+!7 = !DINamespace(name: "core", scope: null)
+!8 = !DIBasicType(name: "u8", size: 8, encoding: DW_ATE_unsigned)
+!9 = !{!10, !11}
+!10 = !DIEnumerator(name: "None", value: 0)
+!11 = !DIEnumerator(name: "Some", value: 1)
+!12 = !DILocalVariable(name: "msg", arg: 2, scope: !13, file: !14, line: 689, type: !17)
+!13 = distinct !DISubprogram(name: "expect<()>", linkageName: "_ZN4core6option15Option$LT$T$GT$6expect17h9a574c18f194c213E", scope: !4, file: !14, line: 689, type: !15, scopeLine: 689, flags: DIFlagPrototyped, spFlags: DISPFlagLocalToUnit | DISPFlagDefinition | DISPFlagOptimized, unit: !1, templateParams: !24, retainedNodes: !23)
+!14 = !DIFile(filename: "/rustc/ec4bcaac450279b029f3480b8b8f1b82ab36a5eb/library/core/src/option.rs", directory: "", checksumkind: CSK_MD5, checksum: "4120c8557937a0772190a676ec193800")
+!15 = !DISubroutineType(types: !16)
+!16 = !{null, !4, !17}
+!17 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "&str", file: !5, size: 128, align: 64, elements: !18, templateParams: !23, identifier: "84eec819988617519061e0b609a72fe3")
+!18 = !{!19, !21}
+!19 = !DIDerivedType(tag: DW_TAG_member, name: "data_ptr", scope: !17, file: !5, baseType: !20, size: 64, align: 64)
+!20 = !DIDerivedType(tag: DW_TAG_pointer_type, name: "*const u8", baseType: !8, size: 64, align: 64, dwarfAddressSpace: 0)
+!21 = !DIDerivedType(tag: DW_TAG_member, name: "length", scope: !17, file: !5, baseType: !22, size: 64, align: 64, offset: 64)
+!22 = !DIBasicType(name: "usize", size: 64, encoding: DW_ATE_unsigned)
+!23 = !{}
+!24 = !{!25}
+!25 = !DITemplateTypeParameter(name: "T", type: !26)
+!26 = !DIBasicType(name: "()", encoding: DW_ATE_unsigned)
+!27 = !DILocation(line: 0, scope: !13)
Index: llvm/lib/CodeGen/SelectionDAG/ScheduleDAGSDNodes.cpp
===================================================================
--- llvm/lib/CodeGen/SelectionDAG/ScheduleDAGSDNodes.cpp
+++ llvm/lib/CodeGen/SelectionDAG/ScheduleDAGSDNodes.cpp
@@ -1060,8 +1060,9 @@
       if (!MI.isDebugValue())
         continue;
 
+      // Only scan up to insertion point.
       if (&MI == InsertPos)
-        InsertPos = std::prev(InsertPos->getIterator());
+        break;
 
       // The DBG_VALUE was referencing a value produced by a terminator. By
       // moving the DBG_VALUE, the referenced value also needs invalidating.


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