From e904d2bfd62795f40e093b733ef910fb70e5af4a Mon Sep 17 00:00:00 2001
From: Jim Blandy <jimb@red-bean.com>
Date: Mon, 7 Feb 2022 14:10:28 -0800
Subject: [PATCH] [msl-out] Document why dot operator on ints requires baking.

---
 src/back/msl/writer.rs | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/src/back/msl/writer.rs b/src/back/msl/writer.rs
index acf787f40b..d0dea3ef17 100644
--- a/src/back/msl/writer.rs
+++ b/src/back/msl/writer.rs
@@ -1856,8 +1856,12 @@ impl<W: Write> Writer<W> {
             if min_ref_count <= expr_info.ref_count {
                 self.need_bake_expressions.insert(expr.0);
             }
-            // if the expression is a Dot product with integer arguments,
-            // then the args needs baking as well
+
+            // WGSL's `dot` function works on any `vecN` type, but Metal's only
+            // works on floating-point vectors, so we emit inline code for
+            // integer vector `dot` calls. But that code uses each argument `N`
+            // times, once for each component (see `put_dot_product`), so to
+            // avoid duplicated evaluation, we must bake integer operands.
             if let (
                 fun_handle,
                 &Expression::Math {