[CIR][Codegen][Bugfix] use record layout to generate index for a field (llvm#270)

This is a minor fix similar to the one introduced in llvm#263.
Basically, all calls to the `buildLValueForFieldInitialization` are even
with the origin codegen `emitLValueForFieldInitialization` calls, i.e.
the field index is calculated from the record layout, but not from the
decl `field->getFieldIndex()`.

Added just one test, because looks like we need to implement some `NYI`
features first to test another places e.g. in `CIRGenExprAgg.cpp`,
though I could miss something.

Anyway, given the original codegen doesn't use `getFieldIndex` in these
places, we also should not.

All the remaining usages of `getFieldIndex` are ok.

Author: gitoleg

clang/lib/CIR/CodeGen/CIRGenClass.cpp

@@ -207,8 +207,7 @@ static void buildLValueForAnyFieldInitialization(CIRGenFunction &CGF,
   if (MemberInit->isIndirectMemberInitializer()) {
     llvm_unreachable("NYI");
   } else {
-    LHS = CGF.buildLValueForFieldInitialization(LHS, Field, Field->getName(),
-                                                Field->getFieldIndex());
+    LHS = CGF.buildLValueForFieldInitialization(LHS, Field, Field->getName());
   }
 }
 

clang/lib/CIR/CodeGen/CIRGenExpr.cpp

@@ -388,13 +388,15 @@ LValue CIRGenFunction::buildLValueForField(LValue base,
 }
 
 LValue CIRGenFunction::buildLValueForFieldInitialization(
-    LValue Base, const clang::FieldDecl *Field, llvm::StringRef FieldName,
-    unsigned FieldIndex) {
+    LValue Base, const clang::FieldDecl *Field, llvm::StringRef FieldName) {
   QualType FieldType = Field->getType();
 
   if (!FieldType->isReferenceType())
     return buildLValueForField(Base, Field);
 
+  auto& layout = CGM.getTypes().getCIRGenRecordLayout(Field->getParent());
+  unsigned FieldIndex = layout.getCIRFieldNo(Field);
+  
   Address V = buildAddrOfFieldStorage(*this, Base.getAddress(), Field,
                                       FieldName, FieldIndex);
 

clang/lib/CIR/CodeGen/CIRGenExprAgg.cpp

@@ -9,7 +9,6 @@
 // This contains code to emit Aggregate Expr nodes as CIR code.
 //
 //===----------------------------------------------------------------------===//
-
 #include "CIRGenCall.h"
 #include "CIRGenFunction.h"
 #include "CIRGenModule.h"
@@ -554,7 +553,7 @@ void AggExprEmitter::VisitLambdaExpr(LambdaExpr *E) {
 
     // Emit initialization
     LValue LV = CGF.buildLValueForFieldInitialization(
-        SlotLV, *CurField, fieldName, CurField->getFieldIndex());
+        SlotLV, *CurField, fieldName);
     if (CurField->hasCapturedVLAType()) {
       llvm_unreachable("NYI");
     }
@@ -819,9 +818,8 @@ void AggExprEmitter::VisitCXXParenListOrInitListExpr(
     if (curInitIndex == NumInitElements && Dest.isZeroed() &&
         CGF.getTypes().isZeroInitializable(ExprToVisit->getType()))
       break;
-
     LValue LV = CGF.buildLValueForFieldInitialization(
-        DestLV, field, field->getName(), field->getFieldIndex());
+        DestLV, field, field->getName());
     // We never generate write-barries for initialized fields.
     assert(!UnimplementedFeature::setNonGC());
 

clang/lib/CIR/CodeGen/CIRGenFunction.h

@@ -1531,8 +1531,7 @@ class CIRGenFunction : public CIRGenTypeCache {
   /// stored in the reference.
   LValue buildLValueForFieldInitialization(LValue Base,
                                            const clang::FieldDecl *Field,
-                                           llvm::StringRef FieldName,
-                                           unsigned FieldIndex);
+                                           llvm::StringRef FieldName);
 
   void buildInitializerForField(clang::FieldDecl *Field, LValue LHS,
                                 clang::Expr *Init);

clang/test/CIR/CodeGen/derived-to-base.cpp

@@ -156,3 +156,16 @@ void t() {
   B b;
   b.foo();
 }
+
+struct C : public A {
+  int& ref;
+  C(int& x) : ref(x) {}
+};
+
+// CHECK: cir.func @_Z8test_refv()
+// CHECK: cir.get_member %2[1] {name = "ref"} 
+int test_ref() {
+  int x = 42;
+  C c(x);
+  return c.ref;
+}