From: Reid Kleckner <rnk@google.com>
Date: Wed, 31 Aug 2016 20:35:01 +0000 (+0000)
Subject: [codeview] Don't emit vshape info for classes without vfptrs
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=3a4bcdc687c7076c6a0a602786b2c72f6e2d243c;p=clang

[codeview] Don't emit vshape info for classes without vfptrs

Classes with no virtual methods or whose virtual methods were all
inherited from virtual bases don't have a vfptr at offset zero. We were
crashing attempting to get the layout of that non-existent vftable.

We don't need any vshape info in this case because the debugger can
infer it from the base class information. The current class may not
introduce any virtual methods if we are in this situation.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@280287 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/CodeGen/CGDebugInfo.cpp b/lib/CodeGen/CGDebugInfo.cpp
index 00e0da4d9f..fbbf23a96b 100644
--- a/lib/CodeGen/CGDebugInfo.cpp
+++ b/lib/CodeGen/CGDebugInfo.cpp
@@ -1555,6 +1555,14 @@ void CGDebugInfo::CollectVTableInfo(const CXXRecordDecl *RD, llvm::DIFile *Unit,
   if (!RD->isDynamicClass())
     return;
 
+  // Don't emit any vtable shape or vptr info if this class doesn't have an
+  // extendable vfptr. This can happen if the class doesn't have virtual
+  // methods, or in the MS ABI if those virtual methods only come from virtually
+  // inherited bases.
+  const ASTRecordLayout &RL = CGM.getContext().getASTRecordLayout(RD);
+  if (!RL.hasExtendableVFPtr())
+    return;
+
   // CodeView needs to know how large the vtable of every dynamic class is, so
   // emit a special named pointer type into the element list. The vptr type
   // points to this type as well.
@@ -1580,7 +1588,6 @@ void CGDebugInfo::CollectVTableInfo(const CXXRecordDecl *RD, llvm::DIFile *Unit,
   }
 
   // If there is a primary base then the artificial vptr member lives there.
-  const ASTRecordLayout &RL = CGM.getContext().getASTRecordLayout(RD);
   if (RL.getPrimaryBase())
     return;
 
diff --git a/test/CodeGenCXX/debug-info-ms-vbase.cpp b/test/CodeGenCXX/debug-info-ms-vbase.cpp
new file mode 100644
index 0000000000..810212e8d2
--- /dev/null
+++ b/test/CodeGenCXX/debug-info-ms-vbase.cpp
@@ -0,0 +1,54 @@
+// RUN: %clang_cc1 %s -triple=i686-pc-windows-msvc -debug-info-kind=limited -gcodeview -emit-llvm -o - | FileCheck %s
+
+// Tests virtual bases in the MS ABI.
+
+struct POD { int pod; };
+
+struct DynamicNoVFPtr : virtual POD { };
+
+DynamicNoVFPtr dynamic_no_vfptr;
+
+// CHECK: ![[DynamicNoVFPtr:[0-9]+]] = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "DynamicNoVFPtr",
+// CHECK-SAME: elements: ![[elements:[0-9]+]]
+
+// CHECK: ![[elements]] = !{![[POD_base:[0-9]+]]}
+
+// CHECK: ![[POD_base]] = !DIDerivedType(tag: DW_TAG_inheritance, scope: ![[DynamicNoVFPtr]],
+// CHECK-SAME: baseType: ![[POD:[0-9]+]], offset: 4, flags: DIFlagVirtual)
+
+// CHECK: ![[POD]] = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "POD"
+
+struct HasVirtualMethod { virtual void f(); };
+
+struct NoPrimaryBase : virtual HasVirtualMethod { };
+
+NoPrimaryBase no_primary_base;
+
+// CHECK: ![[NoPrimaryBase:[0-9]+]] = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "NoPrimaryBase",
+// CHECK-SAME: elements: ![[elements:[0-9]+]]
+
+// CHECK: ![[elements]] = !{![[NoPrimaryBase_base:[0-9]+]]}
+
+// CHECK: ![[NoPrimaryBase_base]] = !DIDerivedType(tag: DW_TAG_inheritance, scope: ![[NoPrimaryBase]],
+// CHECK-SAME: baseType: ![[HasVirtualMethod:[0-9]+]], offset: 4, flags: DIFlagVirtual)
+
+// CHECK: ![[HasVirtualMethod]] = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "HasVirtualMethod"
+
+struct SecondaryVTable { virtual void g(); };
+
+struct HasPrimaryBase : virtual SecondaryVTable, HasVirtualMethod { };
+
+HasPrimaryBase has_primary_base;
+
+// CHECK: ![[HasPrimaryBase:[0-9]+]] = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "HasPrimaryBase",
+// CHECK-SAME: elements: ![[elements:[0-9]+]]
+
+// CHECK: ![[elements]] = !{![[SecondaryVTable_base:[0-9]+]], ![[HasVirtualMethod_base:[0-9]+]], ![[vshape:[0-9]+]]}
+
+// CHECK: ![[SecondaryVTable_base]] = !DIDerivedType(tag: DW_TAG_inheritance, scope: ![[HasPrimaryBase]],
+// CHECK-SAME: baseType: ![[SecondaryVTable:[0-9]+]], offset: 4, flags: DIFlagVirtual)
+
+// CHECK: ![[SecondaryVTable]] = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "SecondaryVTable"
+
+// CHECK: ![[HasVirtualMethod_base]] = !DIDerivedType(tag: DW_TAG_inheritance, scope: ![[HasPrimaryBase]], baseType: ![[HasVirtualMethod]])
+