From c03771e1738dae25eccf7726dcc952ad5936ca15 Mon Sep 17 00:00:00 2001
From: Jacob Young <jacobly0@users.noreply.github.com>
Date: Fri, 14 Apr 2023 04:47:33 -0400
Subject: [PATCH] x86_64: fix overflow of extended multiply

---
 src/arch/x86_64/CodeGen.zig | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/arch/x86_64/CodeGen.zig b/src/arch/x86_64/CodeGen.zig
index 196dc330fb..ef6b5e246b 100644
--- a/src/arch/x86_64/CodeGen.zig
+++ b/src/arch/x86_64/CodeGen.zig
@@ -2089,12 +2089,14 @@ fn airMulWithOverflow(self: *Self, inst: Air.Inst.Index) !void {
                         else => {},
                     }
 
+                    // For now, this is the only supported multiply that doesn't fit in a register.
+                    assert(dst_info.bits == 128 and src_pl.data == 64);
                     const dst_abi_size = @intCast(i32, dst_ty.abiSize(self.target.*));
                     const dst_mcv = try self.allocRegOrMem(inst, false);
                     try self.genSetStack(
                         Type.u1,
                         dst_mcv.stack_offset - dst_abi_size,
-                        .{ .eflags = cc },
+                        .{ .immediate = 0 }, // 64x64 -> 128 never overflows
                         .{},
                     );
                     try self.genSetStack(dst_ty, dst_mcv.stack_offset, partial_mcv, .{});