From 387ba2d99b9eb92eedba4242e38e5ce8ff978af4 Mon Sep 17 00:00:00 2001
From: Tanner Gooding <tagoo@outlook.com>
Date: Mon, 24 Jun 2024 13:04:10 -0700
Subject: [PATCH] Update mono to support Unsafe.BitCast

---
 src/mono/mono/mini/intrinsics.c | 119 ++++++++++++++++++++++++++++++++
 1 file changed, 119 insertions(+)

diff --git a/src/mono/mono/mini/intrinsics.c b/src/mono/mono/mini/intrinsics.c
index f4a92af12e386a..e49851daab69af 100644
--- a/src/mono/mono/mini/intrinsics.c
+++ b/src/mono/mono/mini/intrinsics.c
@@ -488,6 +488,125 @@ emit_unsafe_intrinsics (MonoCompile *cfg, MonoMethod *cmethod, MonoMethodSignatu
 		EMIT_NEW_BIALU (cfg, ins, OP_COMPARE, -1, args [0]->dreg, args [1]->dreg);
 		EMIT_NEW_UNALU (cfg, ins, OP_PCEQ, dreg, -1);
 		return ins;
+	} else if (!strcmp (cmethod->name, "BitCast")) {
+		g_assert (ctx);
+		g_assert (ctx->method_inst);
+		g_assert (ctx->method_inst->type_argc == 2);
+		g_assert (fsig->param_count == 1);
+
+		MonoType *tfrom = ctx->method_inst->type_argv [0];
+		if (mini_is_gsharedvt_variable_type (tfrom)) {
+			// FIXME: Handle gsharevt
+			return NULL;
+		}
+
+		MonoTypeEnum tfrom_type = tfrom->type;
+		MonoClass *tfrom_klass = mono_class_from_mono_type_internal (tfrom);
+		if (!m_class_is_valuetype (tfrom_klass)) {
+			return NULL;
+		}
+
+		MonoType *tto = ctx->method_inst->type_argv [1];
+		if (mini_is_gsharedvt_variable_type (tto)) {
+			// FIXME: Handle gsharevt
+			return NULL;
+		}
+
+		MonoTypeEnum tto_type = tto->type;
+		MonoClass *tto_klass = mono_class_from_mono_type_internal (tto);
+		if (!m_class_is_valuetype (tto_klass)) {
+			return NULL;
+		}
+
+		int tfrom_align, tto_align;
+		if (mono_type_size (tfrom, &tfrom_align) != mono_type_size (tto, &tto_align)) {
+			return NULL;
+		}
+
+		guint32 opcode = OP_LDADDR;
+		MonoStackType tfrom_stack = STACK_PTR;
+		MonoStackType tto_stack = STACK_OBJ;
+
+		if (tfrom_type == MONO_TYPE_I4) {
+			if (tto_type == MONO_TYPE_R4) {
+				opcode = OP_MOVE_I4_TO_F;
+				tfrom_stack = STACK_I4;
+				tto_stack = STACK_R4;
+			}
+			else if (tto_type == MONO_TYPE_I4) {
+				opcode = OP_MOVE;
+				tfrom_stack = STACK_I4;
+				tto_stack = STACK_I4;
+			}
+		}
+		else if (tfrom_type == MONO_TYPE_I8) {
+			if (tto_type == MONO_TYPE_R8) {
+				opcode = OP_MOVE_I8_TO_F;
+				tfrom_stack = STACK_I8;
+				tto_stack = STACK_R8;
+			}
+			else if (tto_type == MONO_TYPE_I8) {
+				opcode = OP_MOVE;
+				tfrom_stack = STACK_I8;
+				tto_stack = STACK_I8;
+			}
+		}
+		else if (tfrom_type == MONO_TYPE_R4) {
+			if (tto_type == MONO_TYPE_I4) {
+				opcode = OP_MOVE_F_TO_I4;
+				tfrom_stack = STACK_R4;
+				tto_stack = STACK_I4;
+			}
+			else if (tto_type == MONO_TYPE_R4) {
+				opcode = OP_RMOVE;
+				tfrom_stack = STACK_R4;
+				tto_stack = STACK_R4;
+			}
+		}
+		else if (tfrom_type == MONO_TYPE_R8) {
+			if (tto_type == MONO_TYPE_I8) {
+				opcode = OP_MOVE_F_TO_I8;
+				tfrom_stack = STACK_R8;
+				tto_stack = STACK_I8;
+			}
+			else if (tto_type == MONO_TYPE_R8) {
+				opcode = OP_FMOVE;
+				tfrom_stack = STACK_R8;
+				tto_stack = STACK_R8;
+			}
+		}
+		else if (mini_class_is_simd (cfg, tfrom_klass)) {
+			if (mini_class_is_simd (cfg, tto_klass)) {
+				// FIXME: Ensure that SIMD to SIMD conversions can be handled
+				//
+				// opcode = OP_XMOVE;
+				// tfrom_stack = STACK_VTYPE;
+				// tto_stack = STACK_VTYPE;
+			}
+		}
+
+		if (opcode == OP_LDADDR) {
+			// FIXME:  `reginfo [sreg].born_in > 0' not met
+			//
+			// MonoInst *arg0;
+			// NEW_VARLOADA (cfg, arg0, args [0], tfrom);
+			// arg0->dreg = mono_alloc_preg (cfg);
+			// 
+			// tto = mini_get_underlying_type (tto);
+			// assert(MONO_TYPE_ISSTRUCT (tto));
+			// 
+			// if (cfg->gshared && (tto != ctx->method_inst->type_argv [1]) && mono_class_check_context_used (mono_class_from_mono_type_internal (tto)))
+			// 	cfg->prefer_instances = TRUE;
+			// return mini_emit_memory_load (cfg, tto, arg0, 0, MONO_INST_UNALIGNED);
+
+			return NULL;
+		}
+
+		int dreg = mono_alloc_dreg (cfg, tfrom_stack);
+		EMIT_NEW_UNALU (cfg, ins, opcode, dreg, args [0]->dreg);
+		ins->type = tto_stack;
+		ins->klass = tto_klass;
+		return ins;
 	} else if (!strcmp (cmethod->name, "IsAddressLessThan")) {
 		g_assert (ctx);
 		g_assert (ctx->method_inst);