[os_log] Mark os_log_helper nounwind

Allow the optimizer to remove unnecessary EH cleanups surrounding calls
to os_log_helper, to save some code size.

As a follow-up, it might be worthwhile to add a BasicNoexcept exception
spec to os_log_helper, and to then teach CGCall to emit direct calls for
callees which can't throw. This could save some compile-time.

Differential Revision: https://reviews.llvm.org/D60108

llvm-svn: 357501

clang/lib/CodeGen/CGBuiltin.cpp

@@ -1138,6 +1138,7 @@ llvm::Function *CodeGenFunction::generateBuiltinOSLogHelperFunction(
   Fn->setVisibility(llvm::GlobalValue::HiddenVisibility);
   CGM.SetLLVMFunctionAttributes(GlobalDecl(), FI, Fn);
   CGM.SetLLVMFunctionAttributesForDefinition(nullptr, Fn);
+  Fn->setDoesNotThrow();
 
   // Attach 'noinline' at -Oz.
   if (CGM.getCodeGenOpts().OptimizeSize == 2)

clang/test/CodeGenObjCXX/os_log.mm

@@ -0,0 +1,19 @@
+// RUN: %clang_cc1 %s -emit-llvm -o - -triple x86_64-darwin-apple -fobjc-arc \
+// RUN:   -fexceptions -fcxx-exceptions -O1 | FileCheck %s
+
+// Check that no EH cleanup is emitted around the call to __os_log_helper.
+namespace no_eh_cleanup {
+  void release(int *lock);
+
+  // CHECK-LABEL: define {{.*}} @_ZN13no_eh_cleanup3logERiPcS1_(
+  void log(int &i, char *data, char *buf) {
+      int lock __attribute__((cleanup(release)));
+      // CHECK: call void @__os_log_helper_1_2_2_4_0_8_34(
+      // CHECK-NEXT: call void @_ZN13no_eh_cleanup7releaseEPi
+      __builtin_os_log_format(buf, "%d %{public}s", i, data);
+  }
+
+  // CHECK: define {{.*}} @__os_log_helper_1_2_2_4_0_8_34({{.*}} [[NUW:#[0-9]+]]
+}
+
+// CHECK: attributes [[NUW]] = { {{.*}}nounwind