From dba5df64eacfbcca9727fe8596b186defb30a753 Mon Sep 17 00:00:00 2001
From: Jakub Konka <kubkon@jakubkonka.com>
Date: Thu, 23 Dec 2021 20:51:48 +0100
Subject: [PATCH] stage2: use lowerToRmEnc to lower two-operand imul

Fix mismatched register sizes in codegen.
---
 src/arch/x86_64/CodeGen.zig |  4 ++--
 src/arch/x86_64/Emit.zig    | 13 +++----------
 2 files changed, 5 insertions(+), 12 deletions(-)

diff --git a/src/arch/x86_64/CodeGen.zig b/src/arch/x86_64/CodeGen.zig
index 65bd3b857c..08a926216c 100644
--- a/src/arch/x86_64/CodeGen.zig
+++ b/src/arch/x86_64/CodeGen.zig
@@ -1717,7 +1717,7 @@ fn genIMulOpMir(self: *Self, dst_ty: Type, dst_mcv: MCValue, src_mcv: MCValue) !
                     _ = try self.addInst(.{
                         .tag = .imul_complex,
                         .ops = (Mir.Ops{
-                            .reg1 = dst_reg,
+                            .reg1 = registerAlias(dst_reg, @divExact(src_reg.size(), 8)),
                             .reg2 = src_reg,
                         }).encode(),
                         .data = undefined,
@@ -1766,7 +1766,7 @@ fn genIMulOpMir(self: *Self, dst_ty: Type, dst_mcv: MCValue, src_mcv: MCValue) !
                     _ = try self.addInst(.{
                         .tag = .imul_complex,
                         .ops = (Mir.Ops{
-                            .reg1 = dst_reg,
+                            .reg1 = registerAlias(dst_reg, @divExact(src_reg.size(), 8)),
                             .reg2 = src_reg,
                         }).encode(),
                         .data = undefined,
diff --git a/src/arch/x86_64/Emit.zig b/src/arch/x86_64/Emit.zig
index 83268b5432..0694a6ed2c 100644
--- a/src/arch/x86_64/Emit.zig
+++ b/src/arch/x86_64/Emit.zig
@@ -380,6 +380,7 @@ const Tag = enum {
     @"test",
     brk,
     nop,
+    imul,
     syscall,
     ret_near,
     ret_far,
@@ -635,6 +636,7 @@ inline fn getOpCode(tag: Tag, enc: Encoding, is_one_byte: bool) ?OpCode {
             .cmp => OpCode.oneByte(if (is_one_byte) 0x3a else 0x3b),
             .mov => OpCode.oneByte(if (is_one_byte) 0x8a else 0x8b),
             .lea => OpCode.oneByte(if (is_one_byte) 0x8c else 0x8d),
+            .imul => OpCode.twoByte(0x0f, 0xaf),
             else => null,
         },
         .oi => return switch (tag) {
@@ -1378,16 +1380,7 @@ fn mirIMulComplex(emit: *Emit, inst: Mir.Inst.Index) InnerError!void {
     assert(tag == .imul_complex);
     const ops = Mir.Ops.decode(emit.mir.instructions.items(.ops)[inst]);
     switch (ops.flags) {
-        0b00 => {
-            const encoder = try Encoder.init(emit.code, 4);
-            encoder.rex(.{
-                .w = ops.reg1.size() == 64,
-                .r = ops.reg1.isExtended(),
-                .b = ops.reg2.isExtended(),
-            });
-            encoder.opcode_2byte(0x0f, 0xaf);
-            encoder.modRm_direct(ops.reg1.lowId(), ops.reg2.lowId());
-        },
+        0b00 => return lowerToRmEnc(.imul, ops.reg1, RegisterOrMemory.reg(ops.reg2), emit.code),
         0b10 => {
             const imm = emit.mir.instructions.items(.data)[inst].imm;
             const opc: u8 = if (imm <= math.maxInt(i8)) 0x6b else 0x69;