Add the alloc_size attribute to clang, attempt 2.

This is a recommit of r290149, which was reverted in r290169 due to msan
failures. msan was failing because we were calling
`isMostDerivedAnUnsizedArray` on an invalid designator, which caused us
to read uninitialized memory. To fix this, the logic of the caller of
said function was simplified, and we now have a `!Invalid` assert in
`isMostDerivedAnUnsizedArray`, so we can catch this particular bug more
easily in the future.

Fingers crossed that this patch sticks this time. :)

Original commit message:

This patch does three things:
- Gives us the alloc_size attribute in clang, which lets us infer the
  number of bytes handed back to us by malloc/realloc/calloc/any user
  functions that act in a similar manner.
- Teaches our constexpr evaluator that evaluating some `const` variables
  is OK sometimes. This is why we have a change in
  test/SemaCXX/constant-expression-cxx11.cpp and other seemingly
  unrelated tests. Richard Smith okay'ed this idea some time ago in
  person.
- Uniques some Blocks in CodeGen, which was reviewed separately at
  D26410. Lack of uniquing only really shows up as a problem when
  combined with our new eagerness in the face of const.

llvm-svn: 290297

1 files changed, 14 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CodeGenModule.h b/clang/lib/CodeGen/CodeGenModule.h
index f26c92d5670..5f06ba90cf1 100644
--- a/clang/lib/CodeGen/CodeGenModule.h
+++ b/clang/lib/CodeGen/CodeGenModule.h
@@ -455,6 +455,10 @@ private:
   bool isTriviallyRecursive(const FunctionDecl *F);
   bool shouldEmitFunction(GlobalDecl GD);
 
+  /// Map of the global blocks we've emitted, so that we don't have to re-emit
+  /// them if the constexpr evaluator gets aggressive.
+  llvm::DenseMap<const BlockExpr *, llvm::Constant *> EmittedGlobalBlocks;
+
   /// @name Cache for Blocks Runtime Globals
   /// @{
 
@@ -776,6 +780,16 @@ public:
 
   /// Gets the address of a block which requires no captures.
   llvm::Constant *GetAddrOfGlobalBlock(const BlockExpr *BE, StringRef Name);
+
+  /// Returns the address of a block which requires no caputres, or null if
+  /// we've yet to emit the block for BE.
+  llvm::Constant *getAddrOfGlobalBlockIfEmitted(const BlockExpr *BE) {
+    return EmittedGlobalBlocks.lookup(BE);
+  }
+
+  /// Notes that BE's global block is available via Addr. Asserts that BE
+  /// isn't already emitted.
+  void setAddrOfGlobalBlock(const BlockExpr *BE, llvm::Constant *Addr);
   
   /// Return a pointer to a constant CFString object for the given string.
   ConstantAddress GetAddrOfConstantCFString(const StringLiteral *Literal);