Extend the ExternalASTSource interface to allow the AST source to

provide the layout of records, rather than letting Clang compute
the layout itself. LLDB provides the motivation for this feature:
because various layout-altering attributes (packed, aligned, etc.)
don't get reliably get placed into DWARF, the record layouts computed
by LLDB from the reconstructed records differ from the actual layouts,
and badness occurs. This interface lets the DWARF data drive layout,
so we don't need the attributes preserved to get the answer write.

The testing methodology for this change is fun. I've introduced a
variant of -fdump-record-layouts called -fdump-record-layouts-simple
that always has the simple C format and provides size/alignment/field
offsets. There is also a -cc1 option -foverride-record-layout=<file>
to take the output of -fdump-record-layouts-simple and parse it to
produce a set of overridden layouts, which is introduced into the AST
via a testing-only ExternalASTSource (called
LayoutOverrideSource). Each test contains a number of records to lay
out, which use various layout-changing attributes, and then dumps the
layouts. We then run the test again, using the preprocessor to
eliminate the layout-changing attributes entirely (which would give us
different layouts for the records), but supplying the
previously-computed record layouts. Finally, we diff the layouts
produced from the two runs to be sure that they are identical.

Note that this code makes the assumption that we don't *have* to
provide the offsets of bases or virtual bases to get the layout right,
because the alignment attributes don't affect it. I believe this
assumption holds, but if it does not, we can extend
LayoutOverrideSource to also provide base offset information.

Fixes the Clang side of <rdar://problem/10169539>.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@149055 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 206 insertions, 0 deletions

diff --git a/lib/Frontend/LayoutOverrideSource.cpp b/lib/Frontend/LayoutOverrideSource.cpp
new file mode 100644
index 0000000000..3af2cc2bbe
--- /dev/null
+++ b/lib/Frontend/LayoutOverrideSource.cpp
@@ -0,0 +1,206 @@
+//===--- LayoutOverrideSource.cpp --Override Record Layouts ---------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+#include "clang/Frontend/LayoutOverrideSource.h"
+#include "clang/AST/Decl.h"
+#include "llvm/Support/raw_ostream.h"
+#include <fstream>
+#include <string>
+
+using namespace clang;
+
+/// \brief Parse a simple identifier.
+std::string parseName(StringRef S) {
+  unsigned Offset = 0;
+  while (Offset < S.size() &&
+         (isalpha(S[Offset]) || S[Offset] == '_' ||
+          (Offset > 0 && isdigit(S[Offset]))))
+    ++Offset;
+  
+  return S.substr(0, Offset).str();
+}
+
+LayoutOverrideSource::LayoutOverrideSource(llvm::StringRef Filename) {
+  std::ifstream Input(Filename.str().c_str());
+  if (!Input.is_open())
+    return;
+  
+  // Parse the output of -fdump-record-layouts.
+  std::string CurrentType;
+  Layout CurrentLayout;
+  bool ExpectingType = false;
+  
+  while (Input.good()) {
+    std::string Line;
+    getline(Input, Line);
+    
+    StringRef LineStr(Line);
+
+    // Determine whether the following line will start a 
+    if (LineStr.find("*** Dumping AST Record Layout") != StringRef::npos)  {
+      // Flush the last type/layout, if there is one.
+      if (!CurrentType.empty())
+        Layouts[CurrentType] = CurrentLayout;
+      CurrentLayout = Layout();
+      
+      ExpectingType = true;
+      continue;
+    }
+    
+    // If we're expecting a type, grab it.
+    if (ExpectingType) {
+      ExpectingType = false;
+      
+      StringRef::size_type Pos;
+      if ((Pos = LineStr.find("struct ")) != StringRef::npos)
+        LineStr = LineStr.substr(Pos + strlen("struct "));
+      else if ((Pos = LineStr.find("class ")) != StringRef::npos)
+        LineStr = LineStr.substr(Pos + strlen("class "));
+      else if ((Pos = LineStr.find("union ")) != StringRef::npos)
+        LineStr = LineStr.substr(Pos + strlen("union "));
+      else
+        continue;
+      
+      // Find the name of the type.
+      CurrentType = parseName(LineStr);
+      CurrentLayout = Layout();
+      continue;
+    }
+    
+    // Check for the size of the type.
+    StringRef::size_type Pos = LineStr.find("Size:");
+    if (Pos != StringRef::npos) {
+      // Skip past the "Size:" prefix.
+      LineStr = LineStr.substr(Pos + strlen("Size:"));
+      
+      unsigned long long Size = 0;
+      (void)LineStr.getAsInteger(10, Size);
+      CurrentLayout.Size = Size;
+      continue;
+    }
+
+    // Check for the alignment of the type.
+    Pos = LineStr.find("Alignment:");
+    if (Pos != StringRef::npos) {
+      // Skip past the "Alignment:" prefix.
+      LineStr = LineStr.substr(Pos + strlen("Alignment:"));
+      
+      unsigned long long Alignment = 0;
+      (void)LineStr.getAsInteger(10, Alignment);
+      CurrentLayout.Align = Alignment;
+      continue;
+    }
+    
+    // Check for the size/alignment of the type.
+    Pos = LineStr.find("sizeof=");
+    if (Pos != StringRef::npos) {
+      /* Skip past the sizeof= prefix. */
+      LineStr = LineStr.substr(Pos + strlen("sizeof="));
+
+      // Parse size.
+      unsigned long long Size = 0;
+      (void)LineStr.getAsInteger(10, Size);
+      CurrentLayout.Size = Size;
+
+      Pos = LineStr.find("align=");
+      if (Pos != StringRef::npos) {
+        /* Skip past the align= prefix. */
+        LineStr = LineStr.substr(Pos + strlen("align="));
+        
+        // Parse alignment.
+        unsigned long long Alignment = 0;
+        (void)LineStr.getAsInteger(10, Alignment);
+        CurrentLayout.Align = Alignment;
+      }
+      
+      continue;
+    }
+    
+    // Check for the field offsets of the type.
+    Pos = LineStr.find("FieldOffsets: [");
+    if (Pos == StringRef::npos)
+      continue;
+
+    LineStr = LineStr.substr(Pos + strlen("FieldOffsets: ["));
+    while (!LineStr.empty() && isdigit(LineStr[0])) {
+      // Parse this offset.
+      unsigned Idx = 1;
+      while (Idx < LineStr.size() && isdigit(LineStr[Idx]))
+        ++Idx;
+      
+      unsigned long long Offset = 0;
+      (void)LineStr.substr(0, Idx).getAsInteger(10, Offset);
+      
+      CurrentLayout.FieldOffsets.push_back(Offset);
+      
+      // Skip over this offset, the following comma, and any spaces.
+      LineStr = LineStr.substr(Idx + 1);
+      while (!LineStr.empty() && isspace(LineStr[0]))
+        LineStr = LineStr.substr(1);
+    }
+  }
+  
+  // Flush the last type/layout, if there is one.
+  if (!CurrentType.empty())
+    Layouts[CurrentType] = CurrentLayout;
+}
+
+bool 
+LayoutOverrideSource::layoutRecordType(const RecordDecl *Record,
+  uint64_t &Size, uint64_t &Alignment,
+  llvm::DenseMap<const FieldDecl *, uint64_t> &FieldOffsets,
+  llvm::DenseMap<const CXXRecordDecl *, CharUnits> &BaseOffsets,
+  llvm::DenseMap<const CXXRecordDecl *, CharUnits> &VirtualBaseOffsets) 
+{
+  // We can't override unnamed declarations.
+  if (!Record->getIdentifier())
+    return false;
+  
+  // Check whether we have a layout for this record.
+  llvm::StringMap<Layout>::iterator Known = Layouts.find(Record->getName());
+  if (Known == Layouts.end())
+    return false;
+  
+  // Provide field layouts.
+  unsigned NumFields = 0;
+  for (RecordDecl::field_iterator F = Record->field_begin(), 
+                               FEnd = Record->field_end();
+       F != FEnd; ++F, ++NumFields) {
+    if (NumFields >= Known->second.FieldOffsets.size())
+      continue;
+    
+    FieldOffsets[*F] = Known->second.FieldOffsets[NumFields];
+  }
+  
+  // Wrong number of fields.
+  if (NumFields != Known->second.FieldOffsets.size())
+    return false;
+  
+  Size = Known->second.Size;
+  Alignment = Known->second.Align;
+  return true;
+}
+
+void LayoutOverrideSource::dump() {
+  llvm::raw_ostream &OS = llvm::errs();
+  for (llvm::StringMap<Layout>::iterator L = Layouts.begin(), 
+                                      LEnd = Layouts.end();
+       L != LEnd; ++L) {
+    OS << "Type: blah " << L->first() << '\n';
+    OS << "  Size:" << L->second.Size << '\n';
+    OS << "  Alignment:" << L->second.Align << '\n';
+    OS << "  FieldOffsets: [";
+    for (unsigned I = 0, N = L->second.FieldOffsets.size(); I != N; ++I) {
+      if (I)
+        OS << ", ";
+      OS << L->second.FieldOffsets[I];
+    }
+    OS << "]\n";
+  }
+}
+