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, 38 insertions, 0 deletions

diff --git a/clang/test/CodeGen/builtin-unpredictable.c b/clang/test/CodeGen/builtin-unpredictable.c
new file mode 100644
index 00000000000..b06318e4c89
--- /dev/null
+++ b/clang/test/CodeGen/builtin-unpredictable.c
@@ -0,0 +1,38 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown -emit-llvm -o - %s -O1 | FileCheck %s
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown -emit-llvm -o - %s -O0 | FileCheck %s --check-prefix=CHECK_O0
+
+// When optimizing, the builtin should be converted to metadata.
+// When not optimizing, there should be no metadata created for the builtin.
+// In both cases, the builtin should be removed from the code.
+
+void foo();
+void branch(int x) {
+// CHECK-LABEL: define void @branch(
+
+// CHECK-NOT: builtin_unpredictable
+// CHECK: !unpredictable [[METADATA:.+]]
+// CHECK: [[METADATA]] = !{}
+
+// CHECK_O0-NOT: builtin_unpredictable
+// CHECK_O0-NOT: !unpredictable 
+
+  if (__builtin_unpredictable(x > 0))
+    foo ();
+}
+
+// TODO: Add metadata for unpredictable switches.
+int unpredictable_switch(int x) {
+  switch(__builtin_unpredictable(x)) {
+  default:
+    return 0;
+  case 0:
+  case 1:
+  case 2:
+    return 1;
+  case 5:
+    return 5;
+  };
+
+  return 0;
+}
+