[mono] Cache delegate->method_ptr in MonoDelegateTrampInfo instead of in delegate->method_code.

Repurpose the method_code field to store the MonoDelegateTrampInfo pointer
for future optimizations.

Author: vargaz

src/mono/mono/metadata/object-internals.h

@@ -836,11 +836,8 @@ struct _MonoDelegate {
 	gpointer delegate_trampoline;
 	/* Extra argument passed to the target method in llvmonly mode */
 	gpointer extra_arg;
-	/*
-	 * If non-NULL, this points to a memory location which stores the address of
-	 * the compiled code of the method, or NULL if it is not yet compiled.
-	 */
-	guint8 **method_code;
+	/* MonoDelegateTrampInfo */
+	gpointer invoke_info;
 	gpointer interp_method;
 	/* Interp method that is executed when invoking the delegate */
 	gpointer interp_invoke_impl;

src/mono/mono/metadata/object-offsets.h

@@ -85,7 +85,7 @@ DECL_OFFSET(MonoDelegate, target)
 DECL_OFFSET(MonoDelegate, method_ptr)
 DECL_OFFSET(MonoDelegate, invoke_impl)
 DECL_OFFSET(MonoDelegate, method)
-DECL_OFFSET(MonoDelegate, method_code)
+DECL_OFFSET(MonoDelegate, invoke_info)
 DECL_OFFSET(MonoDelegate, method_is_virtual)
 DECL_OFFSET(MonoDelegate, bound)
 DECL_OFFSET(MonoDelegate, extra_arg)

src/mono/mono/mini/method-to-ir.c

@@ -3692,6 +3692,9 @@ handle_delegate_ctor (MonoCompile *cfg, MonoClass *klass, MonoInst *target, Mono
 		return obj;
 	}
 
+	/* Set invoke_info field */
+	MONO_EMIT_NEW_STORE_MEMBASE (cfg, OP_STORE_MEMBASE_REG, obj->dreg, MONO_STRUCT_OFFSET (MonoDelegate, invoke_info), info_ins->dreg);
+
 	/* Set method field */
 	if (target_method_context_used || invoke_context_used) {
 		// We copy from the delegate trampoline info as it's faster than a rgctx fetch
@@ -3704,21 +3707,6 @@ handle_delegate_ctor (MonoCompile *cfg, MonoClass *klass, MonoInst *target, Mono
 		MONO_EMIT_NEW_STORE_MEMBASE (cfg, OP_STORE_MEMBASE_REG, obj->dreg, MONO_STRUCT_OFFSET (MonoDelegate, method), method_ins->dreg);
 	}
 
-	/*
-	 * To avoid looking up the compiled code belonging to the target method
-	 * in mono_delegate_trampoline (), we allocate a per-domain memory slot to
-	 * store it, and we fill it after the method has been compiled.
-	 */
-	if (!method->dynamic) {
-		MonoInst *code_slot_ins;
-
-		if (target_method_context_used)
-			code_slot_ins = emit_get_rgctx_method (cfg, target_method_context_used, method, MONO_RGCTX_INFO_METHOD_DELEGATE_CODE);
-		else
-			code_slot_ins = mini_emit_runtime_constant (cfg, MONO_PATCH_INFO_METHOD_CODE_SLOT, method);
-		MONO_EMIT_NEW_STORE_MEMBASE (cfg, OP_STORE_MEMBASE_REG, obj->dreg, MONO_STRUCT_OFFSET (MonoDelegate, method_code), code_slot_ins->dreg);
-	}
-
 	/* Set invoke_impl field */
 	dreg = alloc_preg (cfg);
 	MONO_EMIT_NEW_LOAD_MEMBASE (cfg, dreg, info_ins->dreg, MONO_STRUCT_OFFSET (MonoDelegateTrampInfo, invoke_impl));

src/mono/mono/mini/mini-trampolines.c

@@ -1081,8 +1081,8 @@ mono_delegate_trampoline (host_mgreg_t *regs, guint8 *code, gpointer *arg, guint
 	 */
 	if (method && !callvirt) {
 		/* Avoid the overhead of looking up an already compiled method if possible */
-		if (enable_caching && delegate->method_code && *delegate->method_code) {
-			delegate->method_ptr = *delegate->method_code;
+		if (enable_caching && method == tramp_info->method && tramp_info->method_ptr) {
+			delegate->method_ptr = tramp_info->method_ptr;
 		} else {
 			compiled_method = addr = mono_jit_compile_method (method, error);
 			if (!is_ok (error)) {
@@ -1091,8 +1091,6 @@ mono_delegate_trampoline (host_mgreg_t *regs, guint8 *code, gpointer *arg, guint
 			}
 			addr = mini_add_method_trampoline (method, compiled_method, need_rgctx_tramp, need_unbox_tramp);
 			delegate->method_ptr = addr;
-			if (enable_caching && delegate->method_code)
-				*delegate->method_code = (guint8 *)delegate->method_ptr;
 		}
 	} else {
 		if (need_rgctx_tramp)