Improve debug info generated with enabled AddressSanitizer.

When ASan replaces <alloca instruction> with
<offset into a common large alloca>, it should also patch
llvm.dbg.declare calls and replace debug info descriptors to mark
that we've replaced alloca with a value that stores an address
of the user variable, not the user variable itself.

See PR11818 for more context.

llvm-svn: 169984

llvm/include/llvm/DebugInfo.h

@@ -635,6 +635,7 @@ namespace llvm {
       DIFile F = getFieldAs<DIFile>(3);
       return F.getCompileUnit();
     }
+    DIFile getFile() const              { return getFieldAs<DIFile>(3); }
     unsigned getLineNumber() const      {
       return (getUnsignedField(4) << 8) >> 8;
     }

llvm/include/llvm/Transforms/Utils/Local.h

@@ -252,6 +252,11 @@ bool LowerDbgDeclare(Function &F);
 /// an alloca, if any.
 DbgDeclareInst *FindAllocaDbgDeclare(Value *V);
 
+/// replaceDbgDeclareForAlloca - Replaces llvm.dbg.declare instruction when
+/// alloca is replaced with a new value.
+bool replaceDbgDeclareForAlloca(AllocaInst *AI, Value *NewAllocaAddress,
+                                DIBuilder &Builder);
+
 } // End llvm namespace
 
 #endif

llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp

@@ -25,6 +25,7 @@
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/Triple.h"
 #include "llvm/DataLayout.h"
+#include "llvm/DIBuilder.h"
 #include "llvm/Function.h"
 #include "llvm/IRBuilder.h"
 #include "llvm/InlineAsm.h"
@@ -38,6 +39,7 @@
 #include "llvm/Support/system_error.h"
 #include "llvm/Target/TargetMachine.h"
 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
+#include "llvm/Transforms/Utils/Local.h"
 #include "llvm/Transforms/Utils/ModuleUtils.h"
 #include "llvm/Type.h"
 #include <algorithm>
@@ -1158,6 +1160,7 @@ bool AddressSanitizer::poisonStackInFunction(Function &F) {
   SmallVector<Instruction*, 8> RetVec;
   uint64_t TotalSize = 0;
   bool HavePoisonedAllocas = false;
+  DIBuilder DIB(*F.getParent());
 
   // Filter out Alloca instructions we want (and can) handle.
   // Collect Ret instructions.
@@ -1228,6 +1231,7 @@ bool AddressSanitizer::poisonStackInFunction(Function &F) {
     Value *NewAllocaPtr = IRB.CreateIntToPtr(
             IRB.CreateAdd(LocalStackBase, ConstantInt::get(IntptrTy, Pos)),
             AI->getType());
+    replaceDbgDeclareForAlloca(AI, NewAllocaPtr, DIB);
     AI->replaceAllUsesWith(NewAllocaPtr);
     // Analyze lifetime intrinsics only for static allocas we handle.
     if (CheckLifetime)

llvm/lib/Transforms/Utils/Local.cpp

@@ -928,3 +928,38 @@ DbgDeclareInst *llvm::FindAllocaDbgDeclare(Value *V) {
 
   return 0;
 }
+
+bool llvm::replaceDbgDeclareForAlloca(AllocaInst *AI, Value *NewAllocaAddress,
+                                      DIBuilder &Builder) {
+  DbgDeclareInst *DDI = FindAllocaDbgDeclare(AI);
+  if (!DDI)
+    return false;
+  DIVariable DIVar(DDI->getVariable());
+  if (!DIVar.Verify())
+    return false;
+
+  // Create a copy of the original DIDescriptor for user variable, appending
+  // "deref" operation to a list of address elements, as new llvm.dbg.declare
+  // will take a value storing address of the memory for variable, not
+  // alloca itself.
+  Type *Int64Ty = Type::getInt64Ty(AI->getContext());
+  SmallVector<Value*, 4> NewDIVarAddress;
+  if (DIVar.hasComplexAddress()) {
+    for (unsigned i = 0, n = DIVar.getNumAddrElements(); i < n; ++i) {
+      NewDIVarAddress.push_back(
+          ConstantInt::get(Int64Ty, DIVar.getAddrElement(i)));
+    }
+  }
+  NewDIVarAddress.push_back(ConstantInt::get(Int64Ty, DIBuilder::OpDeref));
+  DIVariable NewDIVar = Builder.createComplexVariable(
+      DIVar.getTag(), DIVar.getContext(), DIVar.getName(),
+      DIVar.getFile(), DIVar.getLineNumber(), DIVar.getType(),
+      NewDIVarAddress, DIVar.getArgNumber());
+
+  // Insert llvm.dbg.declare in the same basic block as the original alloca,
+  // and remove old llvm.dbg.declare.
+  BasicBlock *BB = AI->getParent();
+  Builder.insertDeclare(NewAllocaAddress, NewDIVar, BB);
+  DDI->eraseFromParent();
+  return true;
+}

llvm/test/Instrumentation/AddressSanitizer/debug_info.ll

@@ -0,0 +1,60 @@
+; RUN: opt < %s -asan -asan-module -S | FileCheck %s
+
+; Checks that llvm.dbg.declare instructions are updated 
+; accordingly as we merge allocas.
+
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define i32 @_Z3zzzi(i32 %p) nounwind uwtable address_safety {
+entry:
+  %p.addr = alloca i32, align 4
+  %r = alloca i32, align 4
+  store i32 %p, i32* %p.addr, align 4
+  call void @llvm.dbg.declare(metadata !{i32* %p.addr}, metadata !10), !dbg !11
+  call void @llvm.dbg.declare(metadata !{i32* %r}, metadata !12), !dbg !14
+  %0 = load i32* %p.addr, align 4, !dbg !14
+  %add = add nsw i32 %0, 1, !dbg !14
+  store i32 %add, i32* %r, align 4, !dbg !14
+  %1 = load i32* %r, align 4, !dbg !15
+  ret i32 %1, !dbg !15
+}
+
+;   CHECK: define i32 @_Z3zzzi
+;   CHECK: entry:
+; Verify that llvm.dbg.declare calls are in the entry basic block.
+;   CHECK-NOT: %entry
+;   CHECK: call void @llvm.dbg.declare(metadata {{.*}}, metadata ![[ARG_ID:[0-9]+]])
+;   CHECK-NOT: %entry
+;   CHECK: call void @llvm.dbg.declare(metadata {{.*}}, metadata ![[VAR_ID:[0-9]+]])
+
+declare void @llvm.dbg.declare(metadata, metadata) nounwind readnone
+
+!llvm.dbg.cu = !{!0}
+
+!0 = metadata !{i32 786449, i32 0, i32 4, metadata !"a.cc", metadata !"/usr/local/google/llvm_cmake_clang/tmp/debuginfo", metadata !"clang version 3.3 (trunk 169314)", i1 true, i1 false, metadata !"", i32 0, metadata !1, metadata !1, metadata !3, metadata !1} ; [ DW_TAG_compile_unit ] [/usr/local/google/llvm_cmake_clang/tmp/debuginfo/a.cc] [DW_LANG_C_plus_plus]
+!1 = metadata !{metadata !2}
+!2 = metadata !{i32 0}
+!3 = metadata !{metadata !4}
+!4 = metadata !{metadata !5}
+!5 = metadata !{i32 786478, i32 0, metadata !6, metadata !"zzz", metadata !"zzz", metadata !"_Z3zzzi", metadata !6, i32 1, metadata !7, i1 false, i1 true, i32 0, i32 0, null, i32 256, i1 false, i32 (i32)* @_Z3zzzi, null, null, metadata !1, i32 1} ; [ DW_TAG_subprogram ] [line 1] [def] [zzz]
+!6 = metadata !{i32 786473, metadata !"a.cc", metadata !"/usr/local/google/llvm_cmake_clang/tmp/debuginfo", null} ; [ DW_TAG_file_type ]
+!7 = metadata !{i32 786453, i32 0, metadata !"", i32 0, i32 0, i64 0, i64 0, i64 0, i32 0, null, metadata !8, i32 0, i32 0} ; [ DW_TAG_subroutine_type ] [line 0, size 0, align 0, offset 0] [from ]
+!8 = metadata !{metadata !9, metadata !9}
+!9 = metadata !{i32 786468, null, metadata !"int", null, i32 0, i64 32, i64 32, i64 0, i32 0, i32 5} ; [ DW_TAG_base_type ] [int] [line 0, size 32, align 32, offset 0, enc DW_ATE_signed]
+!10 = metadata !{i32 786689, metadata !5, metadata !"p", metadata !6, i32 16777217, metadata !9, i32 0, i32 0} ; [ DW_TAG_arg_variable ] [p] [line 1]
+!11 = metadata !{i32 1, i32 0, metadata !5, null}
+!12 = metadata !{i32 786688, metadata !13, metadata !"r", metadata !6, i32 2, metadata !9, i32 0, i32 0} ; [ DW_TAG_auto_variable ] [r] [line 2]
+
+; Verify that debug descriptors for argument and local variable will be replaced
+; with descriptors that end with OpDeref (encoded as 2).
+;   CHECK: ![[ARG_ID]] = metadata {{.*}} i64 2} ; [ DW_TAG_arg_variable ] [p] [line 1]
+;   CHECK: ![[VAR_ID]] = metadata {{.*}} i64 2} ; [ DW_TAG_auto_variable ] [r] [line 2]
+; Verify that there are no more variable descriptors.
+;   CHECK-NOT: DW_TAG_arg_variable
+;   CHECK-NOT: DW_TAG_auto_variable
+
+
+!13 = metadata !{i32 786443, metadata !5, i32 1, i32 0, metadata !6, i32 0} ; [ DW_TAG_lexical_block ] [/usr/local/google/llvm_cmake_clang/tmp/debuginfo/a.cc]
+!14 = metadata !{i32 2, i32 0, metadata !13, null}
+!15 = metadata !{i32 3, i32 0, metadata !13, null}