From b5fced732416c1d9a2ffa1980ca1af88c06edd83 Mon Sep 17 00:00:00 2001
From: Reid Kleckner <rnk@google.com>
Date: Tue, 9 May 2017 19:59:29 +0000
Subject: [PATCH] [codeview] Check for a DIExpression offset for local
 variables

Fixes inalloca parameters, which previously all pointed to the same
offset. Extend the test to use llvm-readobj so that we can test the
offset in a readable way.

llvm-svn: 302578
---
 llvm/include/llvm/IR/DebugInfoMetadata.h      |  4 ++
 llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp | 10 ++++-
 llvm/lib/IR/DebugInfoMetadata.cpp             | 18 ++++++++
 .../DebugInfo/X86/dbg-declare-inalloca.ll     | 41 +++++++++++++++++++
 4 files changed, 72 insertions(+), 1 deletion(-)

diff --git a/llvm/include/llvm/IR/DebugInfoMetadata.h b/llvm/include/llvm/IR/DebugInfoMetadata.h
index 0331d5229e7f..36bc5ce91b69 100644
--- a/llvm/include/llvm/IR/DebugInfoMetadata.h
+++ b/llvm/include/llvm/IR/DebugInfoMetadata.h
@@ -2276,6 +2276,10 @@ public:
   /// Append \p Ops with operations to apply the \p Offset.
   static void appendOffset(SmallVectorImpl<uint64_t> &Ops, int64_t Offset);
 
+  /// If this is a constant offset, extract it. If there is no expression,
+  /// return true with an offset of zero.
+  bool extractIfOffset(int64_t &Offset) const;
+
   /// Constants for DIExpression::prepend.
   enum { NoDeref = false, WithDeref = true, WithStackValue = true };
 
diff --git a/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
index 87b45c001de4..9d60fff3bccc 100644
--- a/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
@@ -888,13 +888,21 @@ void CodeViewDebug::collectVariableInfoFromMFTable(
     if (!Scope)
       continue;
 
+    // If the variable has an attached offset expression, extract it.
+    // FIXME: Try to handle DW_OP_deref as well.
+    int64_t ExprOffset = 0;
+    if (VI.Expr)
+      if (!VI.Expr->extractIfOffset(ExprOffset))
+        continue;
+
     // Get the frame register used and the offset.
     unsigned FrameReg = 0;
     int FrameOffset = TFI->getFrameIndexReference(*Asm->MF, VI.Slot, FrameReg);
     uint16_t CVReg = TRI->getCodeViewRegNum(FrameReg);
 
     // Calculate the label ranges.
-    LocalVarDefRange DefRange = createDefRangeMem(CVReg, FrameOffset);
+    LocalVarDefRange DefRange =
+        createDefRangeMem(CVReg, FrameOffset + ExprOffset);
     for (const InsnRange &Range : Scope->getRanges()) {
       const MCSymbol *Begin = getLabelBeforeInsn(Range.first);
       const MCSymbol *End = getLabelAfterInsn(Range.second);
diff --git a/llvm/lib/IR/DebugInfoMetadata.cpp b/llvm/lib/IR/DebugInfoMetadata.cpp
index cdbe237766a3..e6c49cad0722 100644
--- a/llvm/lib/IR/DebugInfoMetadata.cpp
+++ b/llvm/lib/IR/DebugInfoMetadata.cpp
@@ -672,6 +672,24 @@ void DIExpression::appendOffset(SmallVectorImpl<uint64_t> &Ops,
   }
 }
 
+bool DIExpression::extractIfOffset(int64_t &Offset) const {
+  if (getNumElements() == 0) {
+    Offset = 0;
+    return true;
+  }
+  if (getNumElements() != 2)
+    return false;
+  if (Elements[0] == dwarf::DW_OP_plus) {
+    Offset = Elements[1];
+    return true;
+  }
+  if (Elements[0] == dwarf::DW_OP_minus) {
+    Offset = -Elements[1];
+    return true;
+  }
+  return false;
+}
+
 DIExpression *DIExpression::prepend(const DIExpression *Expr, bool Deref,
                                     int64_t Offset, bool StackValue) {
   SmallVector<uint64_t, 8> Ops;
diff --git a/llvm/test/DebugInfo/X86/dbg-declare-inalloca.ll b/llvm/test/DebugInfo/X86/dbg-declare-inalloca.ll
index 5301cd661467..e3f5c7e629b8 100644
--- a/llvm/test/DebugInfo/X86/dbg-declare-inalloca.ll
+++ b/llvm/test/DebugInfo/X86/dbg-declare-inalloca.ll
@@ -1,5 +1,6 @@
 ; RUN: llc -O0 < %s | FileCheck %s --check-prefix=CHECK --check-prefix=DEBUG
 ; RUN: llc < %s | FileCheck %s
+; RUN: llc -filetype=obj -O0 < %s | llvm-readobj -codeview - | FileCheck %s --check-prefix=OBJ
 
 ; IR generated by the following source:
 ; struct NonTrivial {
@@ -54,6 +55,46 @@
 ; CHECK:         .asciz  "c"
 ; CHECK:         .cv_def_range    [[start]] [[end]]
 
+; OBJ-LABEL: ProcStart {
+; OBJ:   Kind: S_GPROC32_ID (0x1147)
+; OBJ:   DisplayName: f
+; OBJ: }
+; OBJ: Local {
+; OBJ:   Type: NonTrivial (0x1007)
+; OBJ:   Flags [ (0x1)
+; OBJ:     IsParameter (0x1)
+; OBJ:   ]
+; OBJ:   VarName: a
+; OBJ: }
+; OBJ: DefRangeRegisterRel {
+; OBJ:   BaseRegister: 21
+; OBJ:   BasePointerOffset: 12
+; OBJ: }
+; OBJ: Local {
+; OBJ:   Type: int (0x74)
+; OBJ:   Flags [ (0x1)
+; OBJ:     IsParameter (0x1)
+; OBJ:   ]
+; OBJ:   VarName: b
+; OBJ: }
+; OBJ: DefRangeRegisterRel {
+; OBJ:   BaseRegister: 21
+; OBJ:   BasePointerOffset: 16
+; OBJ: }
+; FIXME: Retain unused.
+; OBJ: Local {
+; OBJ:   Type: int (0x74)
+; OBJ:   Flags [ (0x1)
+; OBJ:     IsParameter (0x1)
+; OBJ:   ]
+; OBJ:   VarName: c
+; OBJ: }
+; OBJ: DefRangeRegisterRel {
+; OBJ:   BaseRegister: 21
+; OBJ:   BasePointerOffset: 24
+; OBJ: }
+; OBJ-LABEL: ProcEnd {
+; OBJ: }
 
 
 ; ModuleID = 't.cpp'