[llvm] [FastISel][DebugInfo] Handle dbg.value targeting allocas (PR #67187)

[Felipe de Azevedo Piovezan via llvm-commits]

https://github.com/felipepiovezan created https://github.com/llvm/llvm-project/pull/67187

FastISel currently drops dbg.values targeting allocas. It may seem surprising that a simple case would fail to be lowered, but dbg.values targeting allocas are not common; we usually have dbg.declares doing that, and those are handled by the common code between FastISel and SelectionDAGISel.

This patch addresses the issue by querying the static alloca map from FuncInfo. If we have a frame index for it, we create a DBG_VALUE intrinsic from it.

>From 9be11058c95003f3ce1da6812c78f6e3130eb53e Mon Sep 17 00:00:00 2001
From: Felipe de Azevedo Piovezan <fpiovezan at apple.com>
Date: Fri, 22 Sep 2023 11:05:03 -0400
Subject: [PATCH] [FastISel][DebugInfo] Handle dbg.value targeting allocas

FastISel currently drops dbg.values targeting allocas. It may seem surprising
that a simple case would fail to be lowered, but dbg.values targeting allocas
are not common; we usually have dbg.declares doing that, and those are handled
by the common code between FastISel and SelectionDAGISel.

This patch addresses the issue by querying the static alloca map from FuncInfo.
If we have a frame index for it, we create a DBG_VALUE intrinsic from it.
---
 llvm/lib/CodeGen/SelectionDAG/FastISel.cpp    |  8 +++++
 .../CodeGen/X86/fast-isel-dbg-value-alloca.ll | 32 +++++++++++++++++++
 2 files changed, 40 insertions(+)
 create mode 100644 llvm/test/CodeGen/X86/fast-isel-dbg-value-alloca.ll

diff --git a/llvm/lib/CodeGen/SelectionDAG/FastISel.cpp b/llvm/lib/CodeGen/SelectionDAG/FastISel.cpp
index f0affce7b6b805c..a831295863399b5 100644
--- a/llvm/lib/CodeGen/SelectionDAG/FastISel.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/FastISel.cpp
@@ -1327,6 +1327,14 @@ bool FastISel::selectIntrinsicCall(const IntrinsicInst *II) {
                         << *DI << "\n");
       return true;
     }
+    if (auto SI = FuncInfo.StaticAllocaMap.find(dyn_cast<AllocaInst>(V));
+        SI != FuncInfo.StaticAllocaMap.end()) {
+      MachineOperand FrameIndexOp = MachineOperand::CreateFI(SI->second);
+      bool IsIndirect = false;
+      BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, MIMD.getDL(), II, IsIndirect,
+              FrameIndexOp, Var, Expr);
+      return true;
+    }
     if (Register Reg = lookUpRegForValue(V)) {
       // FIXME: This does not handle register-indirect values at offset 0.
       if (!FuncInfo.MF->useDebugInstrRef()) {
diff --git a/llvm/test/CodeGen/X86/fast-isel-dbg-value-alloca.ll b/llvm/test/CodeGen/X86/fast-isel-dbg-value-alloca.ll
new file mode 100644
index 000000000000000..77f883ee9bd3a73
--- /dev/null
+++ b/llvm/test/CodeGen/X86/fast-isel-dbg-value-alloca.ll
@@ -0,0 +1,32 @@
+; RUN: llc -fast-isel -fast-isel-abort=1 -mtriple=x86_64-unknown-unknown -stop-after=finalize-isel %s -o - | \
+; RUN:    FileCheck %s
+
+define void @foo(ptr noalias nocapture %arg) !dbg !38 {
+  %k.debug = alloca ptr, align 8
+  store ptr %arg, ptr %k.debug, align 8, !dbg !70
+  call void @llvm.dbg.value(metadata ptr %k.debug, metadata !55, metadata !DIExpression(DW_OP_deref)), !dbg !70
+; CHECK: call void @llvm.dbg.value(metadata ptr %{{.*}}, metadata ![[VAR:.*]], metadata ![[EXPR:.*]])
+; CHECK: DBG_VALUE %stack.0{{.*}}, $noreg, ![[VAR]], ![[EXPR]]
+  ret void, !dbg !70
+}
+
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+!llvm.module.flags = !{!6, !7, !8, !9}
+!llvm.dbg.cu = !{!16}
+
+!6 = !{i32 7, !"Dwarf Version", i32 4}
+!7 = !{i32 2, !"Debug Info Version", i32 3}
+!8 = !{i32 1, !"wchar_size", i32 4}
+!9 = !{i32 8, !"PIC Level", i32 2}
+!16 = distinct !DICompileUnit(language: DW_LANG_Swift, file: !17, producer: "blah", isOptimized: false, runtimeVersion: 5, emissionKind: FullDebug, sysroot: "blah", sdk: "blah")
+!17 = !DIFile(filename: "blah", directory: "blah")
+!38 = distinct !DISubprogram(name: "blah", linkageName: "$blah", scope: !17, file: !17, line: 34, type: !39, scopeLine: 34, spFlags: DISPFlagDefinition, unit: !16, retainedNodes: !43)
+!39 = !DISubroutineType(types: !40)
+!40 = !{!41, !41}
+!41 = !DICompositeType(tag: DW_TAG_structure_type, name: "blah")
+!43 = !{!49, !55}
+!49 = !DILocalVariable(name: "x", arg: 1, scope: !38, file: !17, line: 34, type: !41)
+!55 = !DILocalVariable(name: "k", scope: !56, file: !17, line: 36, type: !41)
+!56 = distinct !DILexicalBlock(scope: !38, file: !17, line: 36, column: 9)
+!70 = !DILocation(line: 36, column: 9, scope: !56)