[PowerPC] Support __builtin_ppc_get_timebase

GCC 4.8+ has a PowerPC-specific intrinsic, __builtin_ppc_get_timebase, to do
what Clang's __builtin_readcyclecounter does. For compatibility with code that
uses GCC's spelling (including glibc), support it as well.

Partially fixes PR23681.

llvm-svn: 246510

clang/include/clang/Basic/BuiltinsPPC.def

@@ -17,6 +17,8 @@
 
 // The format of this database matches clang/Basic/Builtins.def.
 
+BUILTIN(__builtin_ppc_get_timebase, "ULLi", "n")
+
 // This is just a placeholder, the types and attributes are wrong.
 BUILTIN(__builtin_altivec_vaddcuw, "V4UiV4UiV4Ui", "")
 

clang/lib/CodeGen/CGBuiltin.cpp

@@ -6414,6 +6414,11 @@ Value *CodeGenFunction::EmitPPCBuiltinExpr(unsigned BuiltinID,
   switch (BuiltinID) {
   default: return nullptr;
 
+  // __builtin_ppc_get_timebase is GCC 4.8+'s PowerPC-specific name for what we
+  // call __builtin_readcyclecounter.
+  case PPC::BI__builtin_ppc_get_timebase:
+    return Builder.CreateCall(CGM.getIntrinsic(Intrinsic::readcyclecounter));
+
   // vec_ld, vec_lvsl, vec_lvsr
   case PPC::BI__builtin_altivec_lvx:
   case PPC::BI__builtin_altivec_lvxl:

clang/test/CodeGen/builtins-ppc.c

@@ -7,3 +7,10 @@ void test_eh_return_data_regno()
   res = __builtin_eh_return_data_regno(0);  // CHECK: store volatile i32 3
   res = __builtin_eh_return_data_regno(1);  // CHECK: store volatile i32 4
 }
+
+// CHECK-LABEL: define i64 @test_builtin_ppc_get_timebase
+long long test_builtin_ppc_get_timebase() {
+  // CHECK: call i64 @llvm.readcyclecounter()
+  return __builtin_ppc_get_timebase();
+}
+