[llvm] [RemoveDIs] Insert PHIs before debug records in hardware loops (PR #85288)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-debuginfo

Author: Stephen Tozer (SLTozer)

<details>
<summary>Changes</summary>

Fixes: https://github.com/llvm/llvm-project/issues/85254

Hardware loops inserts PHIs at the position `getFirstNonPhi()`, which is incorrect - instead, `getFirstNonPhiIt()` is required to not insert the PHI after any debug records that immediately follow the last existing PHI.

---
Full diff: https://github.com/llvm/llvm-project/pull/85288.diff


2 Files Affected:

- (modified) llvm/lib/CodeGen/HardwareLoops.cpp (+1-1) 
- (added) llvm/test/DebugInfo/ARM/hardware-loop-phi-insertion.ll (+84) 


``````````diff
diff --git a/llvm/lib/CodeGen/HardwareLoops.cpp b/llvm/lib/CodeGen/HardwareLoops.cpp
index c536ec9f79d625..cc5aad14e1b56f 100644
--- a/llvm/lib/CodeGen/HardwareLoops.cpp
+++ b/llvm/lib/CodeGen/HardwareLoops.cpp
@@ -580,7 +580,7 @@ PHINode* HardwareLoop::InsertPHICounter(Value *NumElts, Value *EltsRem) {
   BasicBlock *Preheader = L->getLoopPreheader();
   BasicBlock *Header = L->getHeader();
   BasicBlock *Latch = ExitBranch->getParent();
-  IRBuilder<> Builder(Header->getFirstNonPHI());
+  IRBuilder<> Builder(Header, Header->getFirstNonPHIIt());
   PHINode *Index = Builder.CreatePHI(NumElts->getType(), 2);
   Index->addIncoming(NumElts, Preheader);
   Index->addIncoming(EltsRem, Latch);
diff --git a/llvm/test/DebugInfo/ARM/hardware-loop-phi-insertion.ll b/llvm/test/DebugInfo/ARM/hardware-loop-phi-insertion.ll
new file mode 100644
index 00000000000000..9240bf25b6f63f
--- /dev/null
+++ b/llvm/test/DebugInfo/ARM/hardware-loop-phi-insertion.ll
@@ -0,0 +1,84 @@
+; RUN: llc --stop-after=hardware-loops < %s | FileCheck %s
+
+;; Tests that Hardware Loop Insertion does not insert new phi nodes after debug
+;; records when they appear immediately after the last existing phi node.
+
+; CHECK-LABEL: for.body:
+; CHECK-NEXT: = phi i32
+; CHECK-NEXT: = phi i32
+; CHECK-NEXT: call void @llvm.dbg.value
+
+source_filename = "repro.c"
+target datalayout = "e-m:e-p:32:32-Fi8-i64:64-v128:64:128-a:0:32-n32-S64"
+target triple = "thumbv8.1m.main-arm-none-eabi"
+
+ at z = dso_local local_unnamed_addr global i32 42, align 4, !dbg !0
+ at arr = dso_local local_unnamed_addr global [10 x i32] zeroinitializer, align 4, !dbg !5
+
+define dso_local void @func1() local_unnamed_addr #0 !dbg !18 {
+entry:
+  %0 = load i32, ptr @z, align 4, !tbaa !26
+  br label %for.body, !dbg !30
+
+for.body:                                         ; preds = %entry, %for.body
+  %p1.04 = phi ptr [ @arr, %entry ], [ %incdec.ptr, %for.body ]
+  %i.03 = phi i32 [ 0, %entry ], [ %inc, %for.body ]
+  tail call void @llvm.dbg.value(metadata ptr %p1.04, metadata !23, metadata !DIExpression()), !dbg !25
+  store i32 %0, ptr %p1.04, align 4, !dbg !32, !tbaa !26
+  %inc = add nuw nsw i32 %i.03, 1, !dbg !34
+  %incdec.ptr = getelementptr inbounds i8, ptr %p1.04, i32 4, !dbg !35
+  %exitcond.not = icmp eq i32 %inc, 10, !dbg !36
+  br i1 %exitcond.not, label %for.end, label %for.body, !dbg !30, !llvm.loop !37
+
+for.end:                                          ; preds = %for.body
+  ret void, !dbg !41
+}
+
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!2}
+!llvm.module.flags = !{!11, !12, !13, !14, !15, !16}
+!llvm.ident = !{!17}
+
+!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+!1 = distinct !DIGlobalVariable(name: "z", scope: !2, file: !3, line: 2, type: !8, isLocal: false, isDefinition: true)
+!2 = distinct !DICompileUnit(language: DW_LANG_C11, file: !3, producer: "clang version 19.0.0git", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, globals: !4, splitDebugInlining: false, nameTableKind: None)
+!3 = !DIFile(filename: "repro.c", directory: "/home/gbtozers/dev/upstream-llvm")
+!4 = !{!0, !5}
+!5 = !DIGlobalVariableExpression(var: !6, expr: !DIExpression())
+!6 = distinct !DIGlobalVariable(name: "arr", scope: !2, file: !3, line: 1, type: !7, isLocal: false, isDefinition: true)
+!7 = !DICompositeType(tag: DW_TAG_array_type, baseType: !8, size: 320, elements: !9)
+!8 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!9 = !{!10}
+!10 = !DISubrange(count: 10)
+!11 = !{i32 7, !"Dwarf Version", i32 5}
+!12 = !{i32 2, !"Debug Info Version", i32 3}
+!13 = !{i32 1, !"wchar_size", i32 4}
+!14 = !{i32 1, !"min_enum_size", i32 4}
+!15 = !{i32 7, !"frame-pointer", i32 2}
+!16 = !{i32 7, !"debug-info-assignment-tracking", i1 true}
+!17 = !{!"clang version 19.0.0git"}
+!18 = distinct !DISubprogram(name: "func1", scope: !3, file: !3, line: 4, type: !19, scopeLine: 5, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !2, retainedNodes: !21)
+!19 = !DISubroutineType(types: !20)
+!20 = !{null}
+!21 = !{!23}
+!22 = !DILocalVariable(name: "i", scope: !18, file: !3, line: 6, type: !8)
+!23 = !DILocalVariable(name: "p1", scope: !18, file: !3, line: 7, type: !24)
+!24 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !8, size: 32)
+!25 = !DILocation(line: 0, scope: !18)
+!26 = !{!27, !27, i64 0}
+!27 = !{!"int", !28, i64 0}
+!28 = !{!"omnipotent char", !29, i64 0}
+!29 = !{!"Simple C/C++ TBAA"}
+!30 = !DILocation(line: 8, column: 3, scope: !31)
+!31 = distinct !DILexicalBlock(scope: !18, file: !3, line: 8, column: 3)
+!32 = !DILocation(line: 9, column: 10, scope: !33)
+!33 = distinct !DILexicalBlock(scope: !31, file: !3, line: 8, column: 3)
+!34 = !DILocation(line: 8, column: 27, scope: !33)
+!35 = !DILocation(line: 8, column: 32, scope: !33)
+!36 = !DILocation(line: 8, column: 21, scope: !33)
+!37 = distinct !{!37, !30, !38, !39, !40}
+!38 = !DILocation(line: 9, column: 12, scope: !31)
+!39 = !{!"llvm.loop.mustprogress"}
+!40 = !{!"llvm.loop.unroll.disable"}
+!41 = !DILocation(line: 10, column: 1, scope: !18)

``````````

</details>


https://github.com/llvm/llvm-project/pull/85288