[aot] Store the addresses of aot constants in an array instead of usi…

…ng a switch statement on wasm to save space. (#45669)

Co-authored-by: vargaz <vargaz@users.noreply.github.com>

src/mono/mono/mini/mini-llvm.c

@@ -2945,11 +2945,9 @@ static void
 emit_init_aotconst (MonoLLVMModule *module)
 {
 	LLVMModuleRef lmodule = module->lmodule;
-	LLVMValueRef func, switch_ins;
-	LLVMBasicBlockRef entry_bb, fail_bb, bb;
-	LLVMBasicBlockRef *bbs = NULL;
+	LLVMValueRef func;
+	LLVMBasicBlockRef entry_bb;
 	LLVMBuilderRef builder = LLVMCreateBuilder ();
-	char *name;
 
 	func = LLVMAddFunction (lmodule, module->init_aotconst_symbol, LLVMFunctionType2 (LLVMVoidType (), LLVMInt32Type (), IntPtrType (), FALSE));
 	LLVMSetLinkage (func, LLVMExternalLinkage);
@@ -2959,6 +2957,57 @@ emit_init_aotconst (MonoLLVMModule *module)
 
 	entry_bb = LLVMAppendBasicBlock (func, "ENTRY");
 
+	LLVMPositionBuilderAtEnd (builder, entry_bb);
+
+#ifdef TARGET_WASM
+	/* Emit a table of aotconst addresses instead of a switch statement to save space */
+
+	LLVMValueRef aotconsts;
+	LLVMTypeRef aotconst_addr_type = LLVMPointerType (module->ptr_type, 0);
+	int table_size = module->max_got_offset + 1;
+	LLVMTypeRef aotconst_arr_type = LLVMArrayType (aotconst_addr_type, table_size);
+
+	LLVMValueRef aotconst_dummy = LLVMAddGlobal (module->lmodule, module->ptr_type, "aotconst_dummy");
+	LLVMSetInitializer (aotconst_dummy, LLVMConstNull (module->ptr_type));
+	LLVMSetVisibility (aotconst_dummy, LLVMHiddenVisibility);
+	LLVMSetLinkage (aotconst_dummy, LLVMInternalLinkage);
+
+	aotconsts = LLVMAddGlobal (module->lmodule, aotconst_arr_type, "aotconsts");
+	LLVMValueRef *aotconst_init = g_new0 (LLVMValueRef, table_size);
+	for (int i = 0; i < table_size; ++i) {
+		LLVMValueRef aotconst = (LLVMValueRef)g_hash_table_lookup (module->aotconst_vars, GINT_TO_POINTER (i));
+		if (aotconst)
+			aotconst_init [i] = LLVMConstBitCast (aotconst, aotconst_addr_type);
+		else
+			aotconst_init [i] = LLVMConstBitCast (aotconst_dummy, aotconst_addr_type);
+	}
+	LLVMSetInitializer (aotconsts, LLVMConstArray (aotconst_addr_type, aotconst_init, table_size));
+	LLVMSetVisibility (aotconsts, LLVMHiddenVisibility);
+	LLVMSetLinkage (aotconsts, LLVMInternalLinkage);
+
+	LLVMBasicBlockRef exit_bb = LLVMAppendBasicBlock (func, "EXIT_BB");
+	LLVMBasicBlockRef main_bb = LLVMAppendBasicBlock (func, "BB");
+
+	LLVMValueRef cmp = LLVMBuildICmp (builder, LLVMIntSGE, LLVMGetParam (func, 0), LLVMConstInt (LLVMInt32Type (), table_size, FALSE), "");
+	LLVMBuildCondBr (builder, cmp, exit_bb, main_bb);
+
+	LLVMPositionBuilderAtEnd (builder, main_bb);
+
+	LLVMValueRef indexes [2];
+	indexes [0] = LLVMConstInt (LLVMInt32Type (), 0, FALSE);
+	indexes [1] = LLVMGetParam (func, 0);
+	LLVMValueRef aotconst_addr = LLVMBuildLoad (builder, LLVMBuildGEP (builder, aotconsts, indexes, 2, ""), "");
+	LLVMBuildStore (builder, LLVMBuildIntToPtr (builder, LLVMGetParam (func, 1), module->ptr_type, ""), aotconst_addr);
+	LLVMBuildBr (builder, exit_bb);
+
+	LLVMPositionBuilderAtEnd (builder, exit_bb);
+	LLVMBuildRetVoid (builder);
+#else
+	LLVMValueRef switch_ins;
+	LLVMBasicBlockRef fail_bb, bb;
+	LLVMBasicBlockRef *bbs = NULL;
+	char *name;
+
 	bbs = g_new0 (LLVMBasicBlockRef, module->max_got_offset + 1);
 	for (int i = 0; i < module->max_got_offset + 1; ++i) {
 		name = g_strdup_printf ("BB_%d", i);
@@ -2985,6 +3034,7 @@ emit_init_aotconst (MonoLLVMModule *module)
 	switch_ins = LLVMBuildSwitch (builder, LLVMGetParam (func, 0), fail_bb, 0);
 	for (int i = 0; i < module->max_got_offset + 1; ++i)
 		LLVMAddCase (switch_ins, LLVMConstInt (LLVMInt32Type (), i, FALSE), bbs [i]);
+#endif
 
 	LLVMDisposeBuilder (builder);
 }