some ABI fixups and improvements

Started with trying to enable asan in the CI for MacOS, noticed it wasn't enabled on the `tests/internal`
folder, it came up with a couple of issues with the abi/OdinLLVMBuildTransmute that this also solves.

- Looking at clang output for arm64, we should be promoting `{ i64, i32 }` to `{ i64, i64 }`
- after doing the previous point, I noticed this is not handled well in OdinLLVMBuildTransmute
  which was emitting loads and stores into the space of a value that was alignment, asan does not want this,
  looking at clang output again, a memcpy is the appropriate way of handling this.
- Having done this we don't need the hacky "return is packed" set anymore in the amd64 sysv ABI anymore either

src/llvm_abi.cpp

@@ -977,7 +977,7 @@ namespace lbAbiAmd64SysV {
 			return types[0];
 		}
 
-		return LLVMStructTypeInContext(c, types.data, cast(unsigned)types.count, sz == 0);
+		return LLVMStructTypeInContext(c, types.data, cast(unsigned)types.count, false);
 	}
 
 	gb_internal void classify_with(LLVMTypeRef t, Array<RegClass> *cls, i64 ix, i64 off) {
@@ -1231,38 +1231,24 @@ namespace lbAbiArm64 {
 			}
 		} else {
 			i64 size = lb_sizeof(return_type);
-			if (size <= 16) {
-				LLVMTypeRef cast_type = nullptr;
-
-				if (size == 0) {
-					cast_type = LLVMStructTypeInContext(c, nullptr, 0, false);
-				} else if (size <= 8) {
-					cast_type = LLVMIntTypeInContext(c, cast(unsigned)(size*8));
-				} else {
-					unsigned count = cast(unsigned)((size+7)/8);
-
-					LLVMTypeRef llvm_i64 = LLVMIntTypeInContext(c, 64);
-					LLVMTypeRef *types = gb_alloc_array(temporary_allocator(), LLVMTypeRef, count);
-
-					i64 size_copy = size;
-					for (unsigned i = 0; i < count; i++) {
-						if (size_copy >= 8) {
-							types[i] = llvm_i64;
-						} else {
-							types[i] = LLVMIntTypeInContext(c, 8*cast(unsigned)size_copy);
-						}
-						size_copy -= 8;
-					}
-					GB_ASSERT(size_copy <= 0);
-					cast_type = LLVMStructTypeInContext(c, types, count, true);
-				}
-				return lb_arg_type_direct(return_type, cast_type, nullptr, nullptr);
-			} else {
+			if (size > 16) {
 				LB_ABI_MODIFY_RETURN_IF_TUPLE_MACRO();
 
 				LLVMAttributeRef attr = lb_create_enum_attribute_with_type(c, "sret", return_type);
 				return lb_arg_type_indirect(return_type, attr);
 			}
+
+			GB_ASSERT(size <= 16);
+			LLVMTypeRef cast_type = nullptr;
+			if (size == 0) {
+				cast_type = LLVMStructTypeInContext(c, nullptr, 0, false);
+			} else if (size <= 8) {
+				cast_type = LLVMIntTypeInContext(c, cast(unsigned)(size*8));
+			} else {
+				LLVMTypeRef llvm_i64 = LLVMIntTypeInContext(c, 64);
+				cast_type = LLVMArrayType2(llvm_i64, 2);
+			}
+			return lb_arg_type_direct(return_type, cast_type, nullptr, nullptr);
 		}
 	}
     

src/llvm_backend_general.cpp

@@ -2525,10 +2525,13 @@ general_end:;
 		}
 	}
 
-	src_size = align_formula(src_size, src_align);
-	dst_size = align_formula(dst_size, dst_align);
+	// NOTE(laytan): even though this logic seems sound, the Address Sanitizer does not
+	// want you to load/store the space of a value that is there for alignment.
+#if 0
+	i64 aligned_src_size = align_formula(src_size, src_align);
+	i64 aligned_dst_size = align_formula(dst_size, dst_align);
 
-	if (LLVMIsALoadInst(val) && (src_size >= dst_size && src_align >= dst_align)) {
+	if (LLVMIsALoadInst(val) && (aligned_src_size >= aligned_dst_size && src_align >= dst_align)) {
 		LLVMValueRef val_ptr = LLVMGetOperand(val, 0);
 		val_ptr = LLVMBuildPointerCast(p->builder, val_ptr, LLVMPointerType(dst_type, 0), "");
 		LLVMValueRef loaded_val = OdinLLVMBuildLoad(p, dst_type, val_ptr);
@@ -2536,8 +2539,57 @@ general_end:;
 		// LLVMSetAlignment(loaded_val, gb_min(src_align, dst_align));
 
 		return loaded_val;
+	}
+#endif
+
+	if (src_size > dst_size) {
+		GB_ASSERT(p->decl_block != p->curr_block);
+		// NOTE(laytan): src is bigger than dst, need to memcpy the part of src we want.
+
+		LLVMValueRef val_ptr; 
+		if (LLVMIsALoadInst(val)) {
+			val_ptr = LLVMGetOperand(val, 0);
+		} else if (LLVMIsAAllocaInst(val)) {
+			val_ptr = LLVMBuildPointerCast(p->builder, val, LLVMPointerType(src_type, 0), "");
+		} else {
+			// NOTE(laytan): we need a pointer to memcpy from.
+			LLVMValueRef val_copy = llvm_alloca(p, src_type, src_align);
+			val_ptr = LLVMBuildPointerCast(p->builder, val_copy, LLVMPointerType(src_type, 0), "");
+			LLVMBuildStore(p->builder, val, val_ptr);
+		}
+
+		i64 max_align = gb_max(lb_alignof(src_type), lb_alignof(dst_type));
+		max_align = gb_max(max_align, 16);
+
+		LLVMValueRef ptr = llvm_alloca(p, dst_type, max_align);
+		LLVMValueRef nptr = LLVMBuildPointerCast(p->builder, ptr, LLVMPointerType(dst_type, 0), "");
+
+		LLVMTypeRef types[3] = {
+			lb_type(p->module, t_rawptr),
+			lb_type(p->module, t_rawptr),
+			lb_type(p->module, t_int)
+		};
+
+		LLVMValueRef args[4] = {
+			nptr,
+			val_ptr,
+			LLVMConstInt(LLVMIntTypeInContext(p->module->ctx, 8*cast(unsigned)build_context.int_size), dst_size, 0),
+			LLVMConstInt(LLVMInt1TypeInContext(p->module->ctx), 0, 0),
+		};
+
+		lb_call_intrinsic(
+			p,
+			"llvm.memcpy.inline",
+			args,
+			gb_count_of(args),
+			types,
+			gb_count_of(types)
+		);
+
+		return OdinLLVMBuildLoad(p, dst_type, ptr);
 	} else {
 		GB_ASSERT(p->decl_block != p->curr_block);
+		GB_ASSERT(dst_size >= src_size);
 
 		i64 max_align = gb_max(lb_alignof(src_type), lb_alignof(dst_type));
 		max_align = gb_max(max_align, 16);