Make .bc en/decoding of AttrKind stable

The bitcode representation attribute kinds are encoded into / decoded from
should be independent of the current set of LLVM attributes and their position
in the AttrKind enum. This patch explicitly encodes attributes to fixed bitcode
values.

With this patch applied, LLVM does not silently misread attributes written by
LLVM 3.3. We also enhance the decoding slightly such that an error message is
printed if an unknown AttrKind encoding was dected.

Bonus: Dropping bitcode attributes from AttrKind is now easy, as old AttrKinds
       do not need to be kept to support the Bitcode reader.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187186 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 131 insertions, 2 deletions

diff --git a/lib/Bitcode/Reader/BitcodeReader.cpp b/lib/Bitcode/Reader/BitcodeReader.cpp
index cf827c5..e6d7b50 100644
--- a/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -12,6 +12,7 @@
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/AutoUpgrade.h"
+#include "llvm/Bitcode/LLVMBitCodes.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/DerivedTypes.h"
 #include "llvm/IR/InlineAsm.h"
@@ -22,6 +23,7 @@
 #include "llvm/Support/DataStream.h"
 #include "llvm/Support/MathExtras.h"
 #include "llvm/Support/MemoryBuffer.h"
+#include "llvm/Support/raw_ostream.h"
 using namespace llvm;
 
 enum {
@@ -506,6 +508,125 @@ bool BitcodeReader::ParseAttributeBlock() {
   }
 }
 
+bool BitcodeReader::ParseAttrKind(uint64_t Code, Attribute::AttrKind *Kind) {
+  switch (Code) {
+  case bitc::ATTR_KIND_ALIGNMENT:
+    *Kind = Attribute::Alignment;
+    return false;
+  case bitc::ATTR_KIND_ALWAYS_INLINE:
+    *Kind = Attribute::AlwaysInline;
+    return false;
+  case bitc::ATTR_KIND_BUILTIN:
+    *Kind = Attribute::Builtin;
+    return false;
+  case bitc::ATTR_KIND_BY_VAL:
+    *Kind = Attribute::ByVal;
+    return false;
+  case bitc::ATTR_KIND_COLD:
+    *Kind = Attribute::Cold;
+    return false;
+  case bitc::ATTR_KIND_INLINE_HINT:
+    *Kind = Attribute::InlineHint;
+    return false;
+  case bitc::ATTR_KIND_IN_REG:
+    *Kind = Attribute::InReg;
+    return false;
+  case bitc::ATTR_KIND_MIN_SIZE:
+    *Kind = Attribute::MinSize;
+    return false;
+  case bitc::ATTR_KIND_NAKED:
+    *Kind = Attribute::Naked;
+    return false;
+  case bitc::ATTR_KIND_NEST:
+    *Kind = Attribute::Nest;
+    return false;
+  case bitc::ATTR_KIND_NO_ALIAS:
+    *Kind = Attribute::NoAlias;
+    return false;
+  case bitc::ATTR_KIND_NO_BUILTIN:
+    *Kind = Attribute::NoBuiltin;
+    return false;
+  case bitc::ATTR_KIND_NO_CAPTURE:
+    *Kind = Attribute::NoCapture;
+    return false;
+  case bitc::ATTR_KIND_NO_DUPLICATE:
+    *Kind = Attribute::NoDuplicate;
+    return false;
+  case bitc::ATTR_KIND_NO_IMPLICIT_FLOAT:
+    *Kind = Attribute::NoImplicitFloat;
+    return false;
+  case bitc::ATTR_KIND_NO_INLINE:
+    *Kind = Attribute::NoInline;
+    return false;
+  case bitc::ATTR_KIND_NON_LAZY_BIND:
+    *Kind = Attribute::NonLazyBind;
+    return false;
+  case bitc::ATTR_KIND_NO_RED_ZONE:
+    *Kind = Attribute::NoRedZone;
+    return false;
+  case bitc::ATTR_KIND_NO_RETURN:
+    *Kind = Attribute::NoReturn;
+    return false;
+  case bitc::ATTR_KIND_NO_UNWIND:
+    *Kind = Attribute::NoUnwind;
+    return false;
+  case bitc::ATTR_KIND_OPTIMIZE_FOR_SIZE:
+    *Kind = Attribute::OptimizeForSize;
+    return false;
+  case bitc::ATTR_KIND_READ_NONE:
+    *Kind = Attribute::ReadNone;
+    return false;
+  case bitc::ATTR_KIND_READ_ONLY:
+    *Kind = Attribute::ReadOnly;
+    return false;
+  case bitc::ATTR_KIND_RETURNED:
+    *Kind = Attribute::Returned;
+    return false;
+  case bitc::ATTR_KIND_RETURNS_TWICE:
+    *Kind = Attribute::ReturnsTwice;
+    return false;
+  case bitc::ATTR_KIND_S_EXT:
+    *Kind = Attribute::SExt;
+    return false;
+  case bitc::ATTR_KIND_STACK_ALIGNMENT:
+    *Kind = Attribute::StackAlignment;
+    return false;
+  case bitc::ATTR_KIND_STACK_PROTECT:
+    *Kind = Attribute::StackProtect;
+    return false;
+  case bitc::ATTR_KIND_STACK_PROTECT_REQ:
+    *Kind = Attribute::StackProtectReq;
+    return false;
+  case bitc::ATTR_KIND_STACK_PROTECT_STRONG:
+    *Kind = Attribute::StackProtectStrong;
+    return false;
+  case bitc::ATTR_KIND_STRUCT_RET:
+    *Kind = Attribute::StructRet;
+    return false;
+  case bitc::ATTR_KIND_SANITIZE_ADDRESS:
+    *Kind = Attribute::SanitizeAddress;
+    return false;
+  case bitc::ATTR_KIND_SANITIZE_THREAD:
+    *Kind = Attribute::SanitizeThread;
+    return false;
+  case bitc::ATTR_KIND_SANITIZE_MEMORY:
+    *Kind = Attribute::SanitizeMemory;
+    return false;
+  case bitc::ATTR_KIND_UW_TABLE:
+    *Kind = Attribute::UWTable;
+    return false;
+  case bitc::ATTR_KIND_Z_EXT:
+    *Kind = Attribute::ZExt;
+    return false;
+  default:
+    std::string Buf;
+    raw_string_ostream fmt(Buf);
+    fmt << "Unknown attribute kind (" << Code << ")";
+    fmt.flush();
+    return Error(Buf.c_str());
+  }
+}
+
 bool BitcodeReader::ParseAttributeGroupBlock() {
   if (Stream.EnterSubBlock(bitc::PARAMATTR_GROUP_BLOCK_ID))
     return Error("Malformed block record");
@@ -545,9 +666,16 @@ bool BitcodeReader::ParseAttributeGroupBlock() {
       AttrBuilder B;
       for (unsigned i = 2, e = Record.size(); i != e; ++i) {
         if (Record[i] == 0) {        // Enum attribute
-          B.addAttribute(Attribute::AttrKind(Record[++i]));
+          Attribute::AttrKind Kind;
+          if (ParseAttrKind(Record[++i], &Kind))
+            return true;
+
+          B.addAttribute(Kind);
         } else if (Record[i] == 1) { // Align attribute
-          if (Attribute::AttrKind(Record[++i]) == Attribute::Alignment)
+          Attribute::AttrKind Kind;
+          if (ParseAttrKind(Record[++i], &Kind))
+            return true;
+          if (Kind == Attribute::Alignment)
             B.addAlignmentAttr(Record[++i]);
           else
             B.addStackAlignmentAttr(Record[++i]);
diff --git a/lib/Bitcode/Reader/BitcodeReader.h b/lib/Bitcode/Reader/BitcodeReader.h
index e4de4ab..b095447 100644
--- a/lib/Bitcode/Reader/BitcodeReader.h
+++ b/lib/Bitcode/Reader/BitcodeReader.h
@@ -321,6 +321,7 @@ private:
     return getFnValueByID(ValNo, Ty);
   }
 
+  bool ParseAttrKind(uint64_t Code, Attribute::AttrKind *Kind);
   bool ParseModule(bool Resume);
   bool ParseAttributeBlock();
   bool ParseAttributeGroupBlock();