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

[Felipe de Azevedo Piovezan via llvm-commits]

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

>From 63ed0f48ce2e22533163eba14b03ab546e19d140 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.

One X86 test now generates more debug information and an extra redundant label
that we had to account for.
---
 llvm/lib/CodeGen/SelectionDAG/FastISel.cpp    |  8 +++++
 .../CodeGen/X86/fast-isel-dbg-value-alloca.ll | 32 +++++++++++++++++++
 llvm/test/DebugInfo/COFF/lines-bb-start.ll    |  2 ++
 3 files changed, 42 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)
diff --git a/llvm/test/DebugInfo/COFF/lines-bb-start.ll b/llvm/test/DebugInfo/COFF/lines-bb-start.ll
index 9ff112cf7ae7c35..70c96b368c9ad9b 100644
--- a/llvm/test/DebugInfo/COFF/lines-bb-start.ll
+++ b/llvm/test/DebugInfo/COFF/lines-bb-start.ll
@@ -90,6 +90,8 @@ return:                                           ; preds = %if.end, %if.then
 ; CHECK:         .cv_loc {{.*}} # t.c:4:5
 ; CHECK:         jmp     LBB{{.*}}
 ; CHECK: LBB2_{{.*}}:                                 # %if.end
+; CHECK-NEXT: L{{.*}}:
+; CHECK-NEXT: DEBUG_VALUE: lea_dbg_value:
 ; CHECK-NEXT:    .cv_loc {{.*}} # t.c:5:3
 ; CHECK:         leal 4(%esp), %[[reg:[^ ]*]]
 ; CHECK:         movl    %[[reg]], (%esp)