[Extension] Optimizing passed by-value const objects.

[lvoufo]

Summary

Continued from D13603, handling functions that are defined with const parameters.

[lvoufo]

Update patch (Wrong patch submitted earlier).

[rsmith]

This looks fine (subject to the observation in D13603 that MarkWriteOnceWrittenRAII can just be a function rather than an RAII class type).

lib/CodeGen/CGDecl.cpp

if (CGDebugInfo *DI = getDebugInfo()) {
     if (CGM.getCodeGenOpts().getDebugInfo()
           >= CodeGenOptions::LimitedDebugInfo) {
       DI->EmitDeclareOfArgVariable(&D, DeclPtr.getPointer(), ArgNo, Builder);
     }
   }
 
   if (D.hasAttr<AnnotateAttr>())
     EmitVarAnnotations(&D, DeclPtr.getPointer());
+
+  MarkWriteOnceWrittenRAII MWO(*this, &D);
 }

test/CodeGenCXX/const-invariant.cpp

#endif
   // CHECK-L-CO: call {{.*}} i8* @_Znwm(
   // CHECK-L-CO: call {{.*}}@llvm.invariant.start(i64 {{[0-9]+}}, i8*
   bar(*i_pc);
   foo(i_pc);  // May change *i_p.
   bar(*i_pc);
   // CHECK-L-CO: call {{.*}}@llvm.invariant.end({{.*}}, i64 {{[0-9]+}}, i8*
 }
 
+#ifdef LOCAL
+void ex1_parms(Const Type i) {
+  // CHECK: @_Z9ex1_parms1A(
+  // CHECK-L-CO: store {{.*}} %i
+  // CHECK-L-CO: call {{.*}}@llvm.invariant.start(
+  bar(i);
+  foo(&i);  // May change i.
+  bar(i);
+  // CHECK-L-CO: call {{.*}}@llvm.invariant.end(
+}
+#endif
+
 // CHECK-G-CO-OBJ: call {{.*}}@llvm.invariant.start(i64 {{[0-9]+}}, i8* bitcast ({{.*}} @_ZL1j to i8*))
 // CHECK-G-CO-INT: store {{.*}}, {{.*}}* @_ZL1j

test/CodeGenObjCXX/arc.mm

void test0(__weak id *wp, __weak volatile id *wvp) {
   id y = *wvp = test0_helper();
 }
 
 // rdar://problem/9320648
 struct Test1_helper { Test1_helper(); };
 @interface Test1 @end
 @implementation Test1 { Test1_helper x; } @end
 // CHECK: define internal i8* @"\01-[Test1 .cxx_construct]"(
+// CHECK:      call {{.*}}@llvm.invariant.start(
 // CHECK:      call void @_ZN12Test1_helperC1Ev(
 // CHECK-NEXT: load
 // CHECK-NEXT: bitcast
+// CHECK-NEXT: call {{.*}}@llvm.invariant.end(
 // CHECK-NEXT: ret i8*
 
 void test34(int cond) {
   __strong id strong;
   __weak id weak;
   extern void test34_sink(id *);
   test34_sink(cond ? &strong : 0);
   test34_sink(cond ? &weak : 0);