[CIR][CodeGen] Locally inited structures with bitfields (#463)

The second part of the job started in #412 , now about local structures.

As it was mentioned previously, sometimes the layout for structures with
bit fields inited with constants differ from the originally created in
`CIRRecordLayoutBuilder` and it cause `storeOp` verification fail due to
different structure type was used to allocation.
This PR fix it.
An example:
```
typedef struct {
  int a : 4;
  int b : 5;
  int c;
} D;

void bar () {
  D d = {1,2,3};  
}
```

Well, I can't say I'm proud of these changes - it seems like a type
safety violation, but looks like it's the best we can do here.

The original codegen doesn't have this problem at all, there is just a
`memcpy` there, I provide LLVM IR just for reference:

```
%struct.D = type { i16, i32 }

@__const.bar.d = private unnamed_addr constant { i8, i8, i32 } { i8 33, i8 0, i32 3 }, align 4

; Function Attrs: noinline nounwind optnone uwtable
define dso_local void @bar() #0 {
entry:
  %d = alloca %struct.D, align 4
  call void @llvm.memcpy.p0.p0.i64(ptr align 4 %d, ptr align 4 @__const.bar.d, i64 8, i1 false)
  ret void
}
```

Author: gitoleg

clang/lib/CIR/CodeGen/CIRGenDecl.cpp

@@ -234,6 +234,13 @@ static void emitStoresForConstant(CIRGenModule &CGM, const VarDecl &D,
   //
   // FIXME(cir): This is closer to memcpy behavior but less optimal, instead of
   // copy from a global, we just create a cir.const out of it.
+
+  if (addr.getElementType() != Ty) {
+    auto ptr = addr.getPointer();
+    ptr = builder.createBitcast(ptr.getLoc(), ptr, builder.getPointerTo(Ty));
+    addr = addr.withPointer(ptr, addr.isKnownNonNull());
+  }
+
   auto loc = CGM.getLoc(D.getSourceRange());
   builder.createStore(loc, builder.getConstant(loc, constant), addr);
 }

clang/test/CIR/CodeGen/bitfields.c

@@ -14,6 +14,12 @@ void m() {
   struct __long l;
 }
 
+typedef struct {
+  int a : 4;
+  int b : 5;
+  int c;
+} D;
+
 typedef struct {
   int a : 4;
   int b : 27;
@@ -27,9 +33,12 @@ typedef struct {
   int a : 3;  // one bitfield with size < 8
   unsigned b;
 } T; 
+
+// CHECK: !ty_22D22 = !cir.struct<struct "D" {!cir.int<u, 16>, !cir.int<s, 32>}>
 // CHECK: !ty_22S22 = !cir.struct<struct "S" {!cir.int<u, 32>, !cir.int<u, 32>, !cir.int<u, 16>, !cir.int<u, 32>}>
 // CHECK: !ty_22T22 = !cir.struct<struct "T" {!cir.int<u, 8>, !cir.int<u, 32>} #cir.record.decl.ast>
 // CHECK: !ty_22anon2E122 = !cir.struct<struct "anon.1" {!cir.int<u, 32>} #cir.record.decl.ast>
+// CHECK: !ty_anon_struct = !cir.struct<struct  {!cir.int<u, 8>, !cir.int<u, 8>, !cir.int<s, 32>}>
 // CHECK: !ty_22__long22 = !cir.struct<struct "__long" {!cir.struct<struct "anon.1" {!cir.int<u, 32>} #cir.record.decl.ast>, !cir.int<u, 32>, !cir.ptr<!cir.int<u, 32>>}>
 
 // CHECK: cir.func {{.*@store_field}}
@@ -96,4 +105,14 @@ unsigned load_non_bitfield(S *s) {
 // CHECK: cir.func {{.*@load_one_bitfield}}
 int load_one_bitfield(T* t) {
   return t->a;
+}
+
+// for this struct type we create an anon structure with different storage types in initialization
+// CHECK: cir.func {{.*@createD}}
+// CHECK:   %0 = cir.alloca !ty_22D22, cir.ptr <!ty_22D22>, ["d"] {alignment = 4 : i64}
+// CHECK:   %1 = cir.cast(bitcast, %0 : !cir.ptr<!ty_22D22>), !cir.ptr<!ty_anon_struct>
+// CHECK:   %2 = cir.const(#cir.const_struct<{#cir.int<33> : !u8i, #cir.int<0> : !u8i, #cir.int<3> : !s32i}> : !ty_anon_struct) : !ty_anon_struct
+// CHECK:   cir.store %2, %1 : !ty_anon_struct, cir.ptr <!ty_anon_struct>
+void createD() {
+  D d = {1,2,3};
 }