[CIR][CIRGen] More on dsolocal: visibility improvements (#735)

In this PR, we 
1. implement defaultVisibility as far as dsolocal is concerned,
currently is either MLIR::Visibility isPublic() or isPrivate(). Now, we
don't handle hiddenVisibility and protectedVisibility from AST. I put
missFeature assert so that If in anyway we translate hiddenVisibility or
protectedVisibility into mlir::SymbolTable::Visibility::Private
(hopefully not for it'd be confusing), then we need to revise this
defaultVisibility setting.
2. call setNonAliasAttributes on global op upon discovery of its
initialization, thus we have globals dso_local correctly set.

Still missing is lots of function should have dso_local set, but the all
depend on comDat implementation, which will come from next PR within the
next few days.

clang/lib/CIR/CodeGen/CIRGenCXX.cpp

@@ -253,7 +253,7 @@ mlir::cir::FuncOp CIRGenModule::codegenCXXStructor(GlobalDecl GD) {
   }
   CurCGF = nullptr;
 
-  // TODO: setNonAliasAttributes
+  setNonAliasAttributes(GD, Fn);
   // TODO: SetLLVMFunctionAttributesForDefinition
   return Fn;
 }

clang/lib/CIR/CodeGen/CIRGenModule.cpp

@@ -365,10 +365,13 @@ bool CIRGenModule::MayBeEmittedEagerly(const ValueDecl *Global) {
 }
 
 static bool hasDefaultVisibility(CIRGlobalValueInterface GV) {
-  // TODO: we need to have a precise definition of what is a default visibility.
-  // in the context of MILR and CIR, now we default to
-  assert(!MissingFeatures::setDefaultVisibility());
-  return true;
+  // Since we do not support hidden visibility and private visibility,
+  // we can assume that the default visibility is public or private.
+  // The way we use private visibility now simply is just treating it
+  // as either local or private linkage, or just default for declarations
+  assert(!MissingFeatures::hiddenVisibility());
+  assert(!MissingFeatures::protectedVisibility());
+  return GV.isPublic() || GV.isPrivate();
 }
 
 static bool shouldAssumeDSOLocal(const CIRGenModule &CGM,
@@ -1291,7 +1294,7 @@ void CIRGenModule::buildGlobalVarDefinition(const clang::VarDecl *D,
       GV.setLinkage(mlir::cir::GlobalLinkageKind::WeakAnyLinkage);
   }
 
-  // TODO(cir): setNonAliasAttributes(D, GV);
+  setNonAliasAttributes(D, GV);
 
   if (D->getTLSKind() && !GV.getTlsModelAttr()) {
     if (D->getTLSKind() == VarDecl::TLS_Dynamic)

clang/test/CIR/CodeGen/linkage.c

@@ -19,7 +19,7 @@ int foo(void) {
 // LLVM: define i32 @foo(
 
 static int var = 0;
-// CIR: cir.global "private" internal @var = #cir.int<0> : !s32i
+// CIR: cir.global "private" internal dsolocal @var = #cir.int<0> : !s32i
 int get_var(void) {
   return var;
 }

clang/test/CIR/CodeGen/static.cpp

@@ -19,15 +19,15 @@ static Init __ioinit2(false);
 // BEFORE:      module {{.*}} {
 // BEFORE-NEXT:   cir.func private @_ZN4InitC1Eb(!cir.ptr<!ty_22Init22>, !cir.bool)
 // BEFORE-NEXT:   cir.func private @_ZN4InitD1Ev(!cir.ptr<!ty_22Init22>)
-// BEFORE-NEXT:   cir.global "private" internal @_ZL8__ioinit = ctor : !ty_22Init22 {
+// BEFORE-NEXT:   cir.global "private" internal dsolocal @_ZL8__ioinit = ctor : !ty_22Init22 {
 // BEFORE-NEXT:     %0 = cir.get_global @_ZL8__ioinit : !cir.ptr<!ty_22Init22>
 // BEFORE-NEXT:     %1 = cir.const #true
 // BEFORE-NEXT:     cir.call @_ZN4InitC1Eb(%0, %1) : (!cir.ptr<!ty_22Init22>, !cir.bool) -> ()
 // BEFORE-NEXT:   } dtor {
 // BEFORE-NEXT:      %0 = cir.get_global @_ZL8__ioinit : !cir.ptr<!ty_22Init22>
 // BEFORE-NEXT:      cir.call @_ZN4InitD1Ev(%0) : (!cir.ptr<!ty_22Init22>) -> ()
 // BEFORE-NEXT:   } {ast = #cir.var.decl.ast}
-// BEFORE:        cir.global "private" internal @_ZL9__ioinit2 = ctor : !ty_22Init22 {
+// BEFORE:        cir.global "private" internal dsolocal @_ZL9__ioinit2 = ctor : !ty_22Init22 {
 // BEFORE-NEXT:     %0 = cir.get_global @_ZL9__ioinit2 : !cir.ptr<!ty_22Init22>
 // BEFORE-NEXT:     %1 = cir.const #false
 // BEFORE-NEXT:     cir.call @_ZN4InitC1Eb(%0, %1) : (!cir.ptr<!ty_22Init22>, !cir.bool) -> ()
@@ -43,7 +43,7 @@ static Init __ioinit2(false);
 // AFTER-NEXT:   cir.func private @__cxa_atexit(!cir.ptr<!cir.func<!void (!cir.ptr<!void>)>>, !cir.ptr<!void>, !cir.ptr<i8>)
 // AFTER-NEXT:   cir.func private @_ZN4InitC1Eb(!cir.ptr<!ty_22Init22>, !cir.bool)
 // AFTER-NEXT:   cir.func private @_ZN4InitD1Ev(!cir.ptr<!ty_22Init22>)
-// AFTER-NEXT:   cir.global "private" internal @_ZL8__ioinit =  #cir.zero : !ty_22Init22 {ast = #cir.var.decl.ast}
+// AFTER-NEXT:   cir.global "private" internal dsolocal @_ZL8__ioinit =  #cir.zero : !ty_22Init22 {ast = #cir.var.decl.ast}
 // AFTER-NEXT:   cir.func internal private @__cxx_global_var_init()
 // AFTER-NEXT:     %0 = cir.get_global @_ZL8__ioinit : !cir.ptr<!ty_22Init22>
 // AFTER-NEXT:     %1 = cir.const #true
@@ -55,7 +55,7 @@ static Init __ioinit2(false);
 // AFTER-NEXT:     %6 = cir.get_global @__dso_handle : !cir.ptr<i8>
 // AFTER-NEXT:     cir.call @__cxa_atexit(%4, %5, %6) : (!cir.ptr<!cir.func<!void (!cir.ptr<!void>)>>, !cir.ptr<!void>, !cir.ptr<i8>) -> ()
 // AFTER-NEXT:     cir.return
-// AFTER:        cir.global "private" internal @_ZL9__ioinit2 =  #cir.zero : !ty_22Init22 {ast = #cir.var.decl.ast}
+// AFTER:        cir.global "private" internal dsolocal @_ZL9__ioinit2 =  #cir.zero : !ty_22Init22 {ast = #cir.var.decl.ast}
 // AFTER-NEXT:   cir.func internal private @__cxx_global_var_init.1()
 // AFTER-NEXT:     %0 = cir.get_global @_ZL9__ioinit2 : !cir.ptr<!ty_22Init22>
 // AFTER-NEXT:     %1 = cir.const #false