[ISelDAG] Salvage debug info at isel by referring to frame indices. (#109126)

We can refer to frame index locations when salvaging debug info
for certain nodes, which prevents the compiler from optimizing
out the location.

Author: bevin-hansson

llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

@@ -11237,6 +11237,12 @@ void SelectionDAG::salvageDebugInfo(SDNode &N) {
   if (!N.getHasDebugValue())
     return;
 
+  auto GetLocationOperand = [](SDNode *Node, unsigned ResNo) {
+    if (auto *FISDN = dyn_cast<FrameIndexSDNode>(Node))
+      return SDDbgOperand::fromFrameIdx(FISDN->getIndex());
+    return SDDbgOperand::fromNode(Node, ResNo);
+  };
+
   SmallVector<SDDbgValue *, 2> ClonedDVs;
   for (auto *DV : GetDbgValues(&N)) {
     if (DV->isInvalidated())
@@ -11272,7 +11278,7 @@ void SelectionDAG::salvageDebugInfo(SDNode &N) {
           if (NewLocOps[i].getKind() != SDDbgOperand::SDNODE ||
               NewLocOps[i].getSDNode() != &N)
             continue;
-          NewLocOps[i] = SDDbgOperand::fromNode(N0.getNode(), N0.getResNo());
+          NewLocOps[i] = GetLocationOperand(N0.getNode(), N0.getResNo());
           if (RHSConstant) {
             SmallVector<uint64_t, 3> ExprOps;
             DIExpression::appendOffset(ExprOps, Offset);
@@ -11327,7 +11333,7 @@ void SelectionDAG::salvageDebugInfo(SDNode &N) {
             NewLocOps[i].getSDNode() != &N)
           continue;
 
-        NewLocOps[i] = SDDbgOperand::fromNode(N0.getNode(), N0.getResNo());
+        NewLocOps[i] = GetLocationOperand(N0.getNode(), N0.getResNo());
         DbgExpression = DIExpression::appendOpsToArg(DbgExpression, ExtOps, i);
         Changed = true;
       }
@@ -11350,7 +11356,11 @@ void SelectionDAG::salvageDebugInfo(SDNode &N) {
   }
 
   for (SDDbgValue *Dbg : ClonedDVs) {
-    assert(!Dbg->getSDNodes().empty() &&
+    assert((!Dbg->getSDNodes().empty() ||
+            llvm::any_of(Dbg->getLocationOps(),
+                         [&](const SDDbgOperand &Op) {
+                           return Op.getKind() == SDDbgOperand::FRAMEIX;
+                         })) &&
            "Salvaged DbgValue should depend on a new SDNode");
     AddDbgValue(Dbg, false);
   }

llvm/test/CodeGen/SPARC/salvage-debug-isel.ll

@@ -0,0 +1,69 @@
+; RUN: llc -march=sparc -O1 %s -o - -stop-after=finalize-isel | FileCheck %s
+
+; Debug info salvaging in isel means we should see a location for this variable.
+
+; CHECK-LABEL: name:            a
+; CHECK: DBG_VALUE %stack.0.b, $noreg, ![[#]], !DIExpression(DW_OP_plus_uconst, 3, DW_OP_stack_value)
+
+define dso_local zeroext i16 @a() local_unnamed_addr #0 !dbg !7 {
+entry:
+  %b = alloca [6 x i8], align 1
+  %arrayidx = getelementptr inbounds [6 x i8], ptr %b, i32 0, i32 undef, !dbg !27
+  store i8 4, ptr %arrayidx, align 1, !dbg !28
+  %arrayidx1 = getelementptr inbounds i8, ptr %b, i32 3, !dbg !32
+    #dbg_value(ptr %arrayidx1, !22, !DIExpression(), !25)
+  %0 = load i8, ptr %arrayidx1, align 1, !dbg !33
+  %tobool.not = icmp eq i8 %0, 0, !dbg !35
+  br i1 %tobool.not, label %if.end, label %for.cond, !dbg !36
+
+for.cond:                                         ; preds = %entry, %for.cond
+  br label %for.cond, !dbg !37, !llvm.loop !40
+
+if.end:                                           ; preds = %entry
+  ret i16 undef, !dbg !44
+}
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2, !3, !4, !5}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C11, file: !1, producer: "clang version 20.0.0git.prerel", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "file.c", directory: "/path", checksumkind: CSK_MD5, checksum: "aa7b5139660a2329a6409414c44cc1f6")
+!2 = !{i32 7, !"Dwarf Version", i32 5}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!4 = !{i32 1, !"wchar_size", i32 4}
+!5 = !{i32 7, !"debug-info-assignment-tracking", i1 true}
+!6 = !{!"clang version 20.0.0git.prerel"}
+!7 = distinct !DISubprogram(name: "a", scope: !1, file: !1, line: 2, type: !8, scopeLine: 2, flags: DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !13)
+!8 = !DISubroutineType(types: !9)
+!9 = !{!10}
+!10 = !DIDerivedType(tag: DW_TAG_typedef, name: "uint16_t", file: !11, line: 277, baseType: !12)
+!11 = !DIFile(filename: "stdint.h", directory: "", checksumkind: CSK_MD5, checksum: "d9e8f73f3756bbd642f1729623e09484")
+!12 = !DIBasicType(name: "unsigned short", size: 16, encoding: DW_ATE_unsigned)
+!13 = !{!14, !20, !22}
+!14 = !DILocalVariable(name: "b", scope: !7, file: !1, line: 3, type: !15)
+!15 = !DICompositeType(tag: DW_TAG_array_type, baseType: !16, size: 48, elements: !18)
+!16 = !DIDerivedType(tag: DW_TAG_typedef, name: "int8_t", file: !11, line: 298, baseType: !17)
+!17 = !DIBasicType(name: "signed char", size: 8, encoding: DW_ATE_signed_char)
+!18 = !{!19}
+!19 = !DISubrange(count: 6)
+!20 = !DILocalVariable(name: "c", scope: !7, file: !1, line: 4, type: !21)
+!21 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!22 = !DILocalVariable(name: "d", scope: !7, file: !1, line: 6, type: !23)
+!23 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !16, size: 32)
+!25 = !DILocation(line: 0, scope: !7)
+!27 = !DILocation(line: 5, column: 3, scope: !7)
+!28 = !DILocation(line: 5, column: 8, scope: !7)
+!32 = !DILocation(line: 6, column: 16, scope: !7)
+!33 = !DILocation(line: 7, column: 33, scope: !34)
+!34 = distinct !DILexicalBlock(scope: !7, file: !1, line: 7, column: 7)
+!35 = !DILocation(line: 7, column: 7, scope: !34)
+!36 = !DILocation(line: 7, column: 7, scope: !7)
+!37 = !DILocation(line: 8, column: 5, scope: !38)
+!38 = distinct !DILexicalBlock(scope: !39, file: !1, line: 8, column: 5)
+!39 = distinct !DILexicalBlock(scope: !34, file: !1, line: 8, column: 5)
+!40 = distinct !{!40, !41, !42, !43}
+!41 = !DILocation(line: 8, column: 5, scope: !39)
+!42 = !DILocation(line: 9, column: 7, scope: !39)
+!43 = !{!"llvm.loop.unroll.disable"}
+!44 = !DILocation(line: 10, column: 1, scope: !7)

llvm/test/CodeGen/X86/pr57673.ll

@@ -37,7 +37,7 @@ define void @foo() {
   ; NORMAL-NEXT: {{  $}}
   ; NORMAL-NEXT:   [[MOVUPSrm:%[0-9]+]]:vr128 = MOVUPSrm %stack.1.i, 1, $noreg, 40, $noreg :: (load (s128) from %ir.i4, align 8)
   ; NORMAL-NEXT:   MOVUPSmr $noreg, 1, $noreg, 0, $noreg, killed [[MOVUPSrm]] :: (store (s128) into `ptr null`, align 8)
-  ; NORMAL-NEXT:   DBG_VALUE $noreg, $noreg, !3, !DIExpression(), debug-location !8
+  ; NORMAL-NEXT:   DBG_VALUE_LIST !3, !DIExpression(DW_OP_LLVM_arg, 0, DW_OP_plus_uconst, 40, DW_OP_stack_value), %stack.1.i, %stack.1.i, debug-location !8
   ; NORMAL-NEXT:   [[MOVUPSrm1:%[0-9]+]]:vr128 = MOVUPSrm %stack.1.i, 1, $noreg, 40, $noreg :: (load (s128) from %ir.i6, align 8)
   ; NORMAL-NEXT:   MOVUPSmr $noreg, 1, $noreg, 0, $noreg, killed [[MOVUPSrm1]] :: (store (s128) into `ptr null`, align 8)
   ; NORMAL-NEXT: {{  $}}
@@ -76,7 +76,7 @@ define void @foo() {
   ; INSTRREF-NEXT: {{  $}}
   ; INSTRREF-NEXT:   [[MOVUPSrm:%[0-9]+]]:vr128 = MOVUPSrm %stack.1.i, 1, $noreg, 40, $noreg :: (load (s128) from %ir.i4, align 8)
   ; INSTRREF-NEXT:   MOVUPSmr $noreg, 1, $noreg, 0, $noreg, killed [[MOVUPSrm]] :: (store (s128) into `ptr null`, align 8)
-  ; INSTRREF-NEXT:   DBG_VALUE $noreg, $noreg, !3, !DIExpression(), debug-location !8
+  ; INSTRREF-NEXT:   DBG_VALUE_LIST !3, !DIExpression(DW_OP_LLVM_arg, 0, DW_OP_plus_uconst, 40, DW_OP_stack_value), %stack.1.i, %stack.1.i, debug-location !8
   ; INSTRREF-NEXT:   [[MOVUPSrm1:%[0-9]+]]:vr128 = MOVUPSrm %stack.1.i, 1, $noreg, 40, $noreg :: (load (s128) from %ir.i6, align 8)
   ; INSTRREF-NEXT:   MOVUPSmr $noreg, 1, $noreg, 0, $noreg, killed [[MOVUPSrm1]] :: (store (s128) into `ptr null`, align 8)
   ; INSTRREF-NEXT: {{  $}}