From 9ba9865e5191dcfdcf7ca794e3b26cbf5c6138bb Mon Sep 17 00:00:00 2001
From: Jacob Young <jacobly0@users.noreply.github.com>
Date: Mon, 16 Feb 2026 09:19:33 -0500
Subject: [PATCH] x86_64: allow positive signed imms to match unsigned imm
 patterns

---
 src/codegen/x86_64/Encoding.zig | 10 +--------
 src/codegen/x86_64/Lower.zig    |  2 +-
 src/codegen/x86_64/encoder.zig  | 39 ++++++++++++---------------------
 3 files changed, 16 insertions(+), 35 deletions(-)

diff --git a/src/codegen/x86_64/Encoding.zig b/src/codegen/x86_64/Encoding.zig
index 6043fd06b50dad070dd5741442d5781dbcc724c6..342a8015bba6b0fc17a586ef3dc6444253f473d9 100644
--- a/src/codegen/x86_64/Encoding.zig
+++ b/src/codegen/x86_64/Encoding.zig
@@ -649,15 +649,7 @@ pub const Op = enum {
             },
 
             .imm => |imm| switch (imm) {
-                .signed => |x| if (x == 1)
-                    .unity
-                else if (math.cast(i8, x)) |_|
-                    .imm8s
-                else if (math.cast(i16, x)) |_|
-                    .imm16s
-                else
-                    .imm32s,
-                .unsigned => |x| if (x == 1)
+                inline .signed, .unsigned => |x| if (x == 1)
                     .unity
                 else if (math.cast(i8, x)) |_|
                     .imm8s
diff --git a/src/codegen/x86_64/Lower.zig b/src/codegen/x86_64/Lower.zig
index 995f044852e360628e3621cbae7adee3ca3b0f24..b93c08b1b58770b792d6afa621ffee0a5c0dfd3b 100644
--- a/src/codegen/x86_64/Lower.zig
+++ b/src/codegen/x86_64/Lower.zig
@@ -565,7 +565,7 @@ fn generic(lower: *Lower, inst: Mir.Inst) Error!void {
         .rmi => &.{
             .{ .reg = inst.data.rix.r1 },
             .{ .mem = lower.mem(1, inst.data.rix.payload) },
-            .{ .imm = if (std.math.cast(u8, inst.data.rix.i)) |u| .u(u) else .s(inst.data.rix.i) },
+            .{ .imm = .s(inst.data.rix.i) },
         },
         .rmi_s, .rmi_u => &.{
             .{ .reg = inst.data.rx.r1 },
diff --git a/src/codegen/x86_64/encoder.zig b/src/codegen/x86_64/encoder.zig
index 1d9c67175ef204933a5463393cad189d0e59e7fa..dd5229f3d349548caee9f6ab3f37bc82ef24e8b6 100644
--- a/src/codegen/x86_64/encoder.zig
+++ b/src/codegen/x86_64/encoder.zig
@@ -43,17 +43,11 @@ pub const Instruction = struct {
 
         pub fn asSigned(imm: Immediate, bit_size: u64) i64 {
             return switch (imm) {
-                .signed => |x| switch (bit_size) {
-                    1, 8 => @as(i8, @intCast(x)),
-                    16 => @as(i16, @intCast(x)),
-                    32, 64 => x,
-                    else => unreachable,
-                },
-                .unsigned => |x| switch (bit_size) {
-                    1, 8 => @as(i8, @bitCast(@as(u8, @intCast(x)))),
-                    16 => @as(i16, @bitCast(@as(u16, @intCast(x)))),
-                    32 => @as(i32, @bitCast(@as(u32, @intCast(x)))),
-                    64 => @bitCast(x),
+                inline .signed, .unsigned => |x| switch (bit_size) {
+                    1, 8 => @as(i8, if (x < 0) @intCast(x) else @bitCast(@as(u8, @intCast(x)))),
+                    16 => @as(i16, if (x < 0) @intCast(x) else @bitCast(@as(u16, @intCast(x)))),
+                    32 => @as(i32, if (x < 0) @intCast(x) else @bitCast(@as(u32, @intCast(x)))),
+                    64 => @as(i64, if (x < 0) @intCast(x) else @bitCast(@as(u64, @intCast(x)))),
                     else => unreachable,
                 },
             };
@@ -61,17 +55,11 @@ pub const Instruction = struct {
 
         pub fn asUnsigned(imm: Immediate, bit_size: u64) u64 {
             return switch (imm) {
-                .signed => |x| switch (bit_size) {
-                    1, 8 => @as(u8, @bitCast(@as(i8, @intCast(x)))),
-                    16 => @as(u16, @bitCast(@as(i16, @intCast(x)))),
-                    32, 64 => @as(u32, @bitCast(x)),
-                    else => unreachable,
-                },
-                .unsigned => |x| switch (bit_size) {
-                    1, 8 => @as(u8, @intCast(x)),
-                    16 => @as(u16, @intCast(x)),
-                    32 => @as(u32, @intCast(x)),
-                    64 => x,
+                inline .signed, .unsigned => |x| switch (bit_size) {
+                    1, 8 => @as(u8, if (x < 0) @bitCast(@as(i8, @intCast(x))) else @intCast(x)),
+                    16 => @as(u16, if (x < 0) @bitCast(@as(i16, @intCast(x))) else @intCast(x)),
+                    32 => @as(u32, if (x < 0) @bitCast(@as(i32, @intCast(x))) else @intCast(x)),
+                    64 => @as(u64, if (x < 0) @bitCast(@as(i64, @intCast(x))) else @intCast(x)),
                     else => unreachable,
                 },
             };
@@ -712,9 +700,10 @@ pub const Instruction = struct {
         }
     }
 
-    fn encodeImm(imm: Immediate, kind: Encoding.Op, encoder: anytype) !void {
-        const raw = imm.asUnsigned(kind.immBitSize());
-        switch (kind.immBitSize()) {
+    fn encodeImm(imm: Immediate, enc_op: Encoding.Op, encoder: anytype) !void {
+        const bit_size = enc_op.immBitSize();
+        const raw = imm.asUnsigned(bit_size);
+        switch (bit_size) {
             8 => try encoder.imm8(@as(u8, @intCast(raw))),
             16 => try encoder.imm16(@as(u16, @intCast(raw))),
             32 => try encoder.imm32(@as(u32, @intCast(raw))),
-- 
2.54.0