From e7c9a6cae09d99388d8384ca7c0fb5b24b353975 Mon Sep 17 00:00:00 2001
From: Nikita Popov <npopov@redhat.com>
Date: Mon, 17 Jan 2022 15:48:01 +0100
Subject: [PATCH] [SDAG] Don't move DBG_VALUE instructions after insertion
 point during scheduling (PR53243)

EmitSchedule() shouldn't be touching instructions after the provided
insertion point. The change introduced in 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.

Fixes https://github.com/llvm/llvm-project/issues/53243.

Differential Revision: https://reviews.llvm.org/D117489
---
 .../SelectionDAG/ScheduleDAGSDNodes.cpp       |  7 ++--
 .../CodeGen/X86/pr53243-tail-call-fastisel.ll | 39 +++++++++++++++++++
 2 files changed, 43 insertions(+), 3 deletions(-)
 create mode 100644 llvm/test/CodeGen/X86/pr53243-tail-call-fastisel.ll

diff --git a/llvm/lib/CodeGen/SelectionDAG/ScheduleDAGSDNodes.cpp b/llvm/lib/CodeGen/SelectionDAG/ScheduleDAGSDNodes.cpp
index bec240d6c4d4..403f34573899 100644
--- a/llvm/lib/CodeGen/SelectionDAG/ScheduleDAGSDNodes.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/ScheduleDAGSDNodes.cpp
@@ -1057,12 +1057,13 @@ EmitSchedule(MachineBasicBlock::iterator &InsertPos) {
            "first terminator cannot be a debug value");
     for (MachineInstr &MI : make_early_inc_range(
              make_range(std::next(FirstTerm), InsertBB->end()))) {
+      // Only scan up to insertion point.
+      if (&MI == InsertPos)
+        break;
+
       if (!MI.isDebugValue())
         continue;
 
-      if (&MI == InsertPos)
-        InsertPos = std::prev(InsertPos->getIterator());
-
       // The DBG_VALUE was referencing a value produced by a terminator. By
       // moving the DBG_VALUE, the referenced value also needs invalidating.
       MI.getOperand(0).ChangeToRegister(0, false);
diff --git a/llvm/test/CodeGen/X86/pr53243-tail-call-fastisel.ll b/llvm/test/CodeGen/X86/pr53243-tail-call-fastisel.ll
new file mode 100644
index 000000000000..333eff8fb008
--- /dev/null
+++ b/llvm/test/CodeGen/X86/pr53243-tail-call-fastisel.ll
@@ -0,0 +1,39 @@
+; 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@PLT # TAILCALL
+  tail call void @set_state()
+  call void @llvm.dbg.value(metadata i64 0, metadata !10, metadata !DIExpression()), !dbg !16
+  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", file: !5, baseType: !6, size: 8, align: 8, flags: DIFlagEnumClass, elements: !7)
+!5 = !DIFile(filename: "<unknown>", directory: "")
+!6 = !DIBasicType(name: "u8", size: 8, encoding: DW_ATE_unsigned)
+!7 = !{!8, !9}
+!8 = !DIEnumerator(name: "None", value: 0)
+!9 = !DIEnumerator(name: "Some", value: 1)
+!10 = !DILocalVariable(name: "msg", arg: 2, scope: !11, file: !12, line: 689, type: !6)
+!11 = distinct !DISubprogram(name: "expect<()>", linkageName: "_ZN4core6option15Option$LT$T$GT$6expect17h9a574c18f194c213E", scope: !4, file: !12, line: 689, type: !13, scopeLine: 689, flags: DIFlagPrototyped, spFlags: DISPFlagLocalToUnit | DISPFlagDefinition | DISPFlagOptimized, unit: !1, templateParams: !15, retainedNodes: !15)
+!12 = !DIFile(filename: "/rustc/ec4bcaac450279b029f3480b8b8f1b82ab36a5eb/library/core/src/option.rs", directory: "", checksumkind: CSK_MD5, checksum: "4120c8557937a0772190a676ec193800")
+!13 = !DISubroutineType(types: !14)
+!14 = !{null, !4}
+!15 = !{}
+!16 = !DILocation(line: 0, scope: !11)