add __builtin_unpredictable and convert to metadata

This patch depends on r246688 (D12341).

The goal is to make LLVM generate different code for these functions for a target that
has cheap branches (see PR23827 for more details):

int foo();

int normal(int x, int y, int z) {
   if (x != 0 && y != 0) return foo();
   return 1;
}

int crazy(int x, int y) {
   if (__builtin_unpredictable(x != 0 && y != 0)) return foo();
   return 1;
}

Differential Revision: http://reviews.llvm.org/D12458

llvm-svn: 246699

1 files changed, 3 insertions, 2 deletions

diff --git a/clang/lib/StaticAnalyzer/Checkers/BuiltinFunctionChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/BuiltinFunctionChecker.cpp
index 104a81e..dab2f61 100644
--- a/clang/lib/StaticAnalyzer/Checkers/BuiltinFunctionChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/BuiltinFunctionChecker.cpp
@@ -41,11 +41,12 @@ bool BuiltinFunctionChecker::evalCall(const CallExpr *CE,
   default:
     return false;
 
+  case Builtin::BI__builtin_unpredictable:
   case Builtin::BI__builtin_expect:
   case Builtin::BI__builtin_assume_aligned:
   case Builtin::BI__builtin_addressof: {
-    // For __builtin_expect and __builtin_assume_aligned, just return the value
-    // of the subexpression.
+    // For __builtin_unpredictable, __builtin_expect, and
+    // __builtin_assume_aligned, just return the value of the subexpression.
     // __builtin_addressof is going from a reference to a pointer, but those
     // are represented the same way in the analyzer.
     assert (CE->arg_begin() != CE->arg_end());