[PATCH] D70752: LowerDbgDeclare: look through bitcasts.

[Evgenii Stepanov via Phabricator via llvm-commits]

eugenis created this revision.
eugenis added reviewers: aprantl, vsk, pcc.
Herald added a subscriber: hiraditya.
Herald added a project: LLVM.
eugenis added a reviewer: echristo.
Herald added a subscriber: ormris.

Emit a value debug intrinsic (with OP_deref) when an alloca address is
passed to a function call after going through a bitcast.

This generates an FP or SP-relative location for the local variable in
the following case:

  int x;
  use((void *)&x;


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D70752

Files:
  llvm/lib/Transforms/Utils/Local.cpp
  llvm/test/Transforms/Util/dbg-call-bitcast.ll


Index: llvm/test/Transforms/Util/dbg-call-bitcast.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/Util/dbg-call-bitcast.ll
@@ -0,0 +1,42 @@
+; RUN: opt -instcombine -S %s | FileCheck %s
+
+define dso_local void @_Z1fv() {
+  %1 = alloca i32, align 4
+  %2 = bitcast i32* %1 to i8*
+  call void @llvm.lifetime.start.p0i8(i64 4, i8* nonnull %2)
+; CHECK: call void @llvm.dbg.value(metadata i32* %1, {{.*}}, metadata !DIExpression(DW_OP_deref)
+  call void @llvm.dbg.declare(metadata i32* %1, metadata !16, metadata !DIExpression()), !dbg !19
+  call void @_Z1gPv(i8* nonnull %2)
+  call void @llvm.lifetime.end.p0i8(i64 4, i8* nonnull %2)
+  ret void, !dbg !21
+}
+
+declare void @llvm.lifetime.start.p0i8(i64 immarg, i8* nocapture)
+declare void @llvm.dbg.declare(metadata, metadata, metadata)
+declare dso_local void @_Z1gPv(i8*)
+declare void @llvm.lifetime.end.p0i8(i64 immarg, i8* nocapture)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!8, !9, !10}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang version 10.0.0 (git at github.com:llvm/llvm-project.git cab64b5708f614c71d275ec9d134e68b8c3baedd)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, retainedTypes: !3, nameTableKind: None)
+!1 = !DIFile(filename: "dbg.cc", directory: "/tmp")
+!2 = !{}
+!3 = !{!4, !5}
+!4 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: null, size: 64)
+!5 = !DISubprogram(name: "g", linkageName: "_Z1gPv", scope: !1, file: !1, line: 1, type: !6, flags: DIFlagPrototyped, spFlags: DISPFlagOptimized, retainedNodes: !2)
+!6 = !DISubroutineType(types: !7)
+!7 = !{null, !4}
+!8 = !{i32 7, !"Dwarf Version", i32 4}
+!9 = !{i32 2, !"Debug Info Version", i32 3}
+!10 = !{i32 1, !"wchar_size", i32 4}
+!12 = distinct !DISubprogram(name: "f", linkageName: "_Z1fv", scope: !1, file: !1, line: 2, type: !13, scopeLine: 2, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !15)
+!13 = !DISubroutineType(types: !14)
+!14 = !{null}
+!15 = !{!16}
+!16 = !DILocalVariable(name: "x", scope: !12, file: !1, line: 3, type: !17)
+!17 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!18 = !DILocation(line: 3, column: 3, scope: !12)
+!19 = !DILocation(line: 3, column: 7, scope: !12)
+!20 = !DILocation(line: 4, column: 3, scope: !12)
+!21 = !DILocation(line: 5, column: 1, scope: !12)
Index: llvm/lib/Transforms/Utils/Local.cpp
===================================================================
--- llvm/lib/Transforms/Utils/Local.cpp
+++ llvm/lib/Transforms/Utils/Local.cpp
@@ -1421,22 +1421,32 @@
         }))
       continue;
 
-    for (auto &AIUse : AI->uses()) {
-      User *U = AIUse.getUser();
-      if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
-        if (AIUse.getOperandNo() == 1)
-          ConvertDebugDeclareToDebugValue(DDI, SI, DIB);
-      } else if (LoadInst *LI = dyn_cast<LoadInst>(U)) {
-        ConvertDebugDeclareToDebugValue(DDI, LI, DIB);
-      } else if (CallInst *CI = dyn_cast<CallInst>(U)) {
-        // This is a call by-value or some other instruction that takes a
-        // pointer to the variable. Insert a *value* intrinsic that describes
-        // the variable by dereferencing the alloca.
-        DebugLoc NewLoc = getDebugValueLoc(DDI, nullptr);
-        auto *DerefExpr =
-            DIExpression::append(DDI->getExpression(), dwarf::DW_OP_deref);
-        DIB.insertDbgValueIntrinsic(AI, DDI->getVariable(), DerefExpr, NewLoc,
-                                    CI);
+    SmallVector<const Value *, 8> WorkList;
+    WorkList.push_back(AI);
+    while (!WorkList.empty()) {
+      const Value *V = WorkList.pop_back_val();
+      for (auto &AIUse : V->uses()) {
+        User *U = AIUse.getUser();
+        if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
+          if (AIUse.getOperandNo() == 1)
+            ConvertDebugDeclareToDebugValue(DDI, SI, DIB);
+        } else if (LoadInst *LI = dyn_cast<LoadInst>(U)) {
+          ConvertDebugDeclareToDebugValue(DDI, LI, DIB);
+        } else if (CallInst *CI = dyn_cast<CallInst>(U)) {
+          // This is a call by-value or some other instruction that takes a
+          // pointer to the variable. Insert a *value* intrinsic that describes
+          // the variable by dereferencing the alloca.
+          if (!CI->isLifetimeStartOrEnd()) {
+            DebugLoc NewLoc = getDebugValueLoc(DDI, nullptr);
+            auto *DerefExpr =
+                DIExpression::append(DDI->getExpression(), dwarf::DW_OP_deref);
+            DIB.insertDbgValueIntrinsic(AI, DDI->getVariable(), DerefExpr,
+                                        NewLoc, CI);
+          }
+        } else if (BitCastInst *BI = dyn_cast<BitCastInst>(U)) {
+          if (BI->getType()->isPointerTy())
+            WorkList.push_back(BI);
+        }
       }
     }
     DDI->eraseFromParent();


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