From 20d5445cb7f0cd9fa614c926173d57d420afccc2 Mon Sep 17 00:00:00 2001
From: Connor Fitzgerald <connorwadefitzgerald@gmail.com>
Date: Thu, 20 Oct 2022 01:37:35 -0400
Subject: [PATCH] Workaround FXC Bug in Matrix Indexing (#2096)

---
 src/back/hlsl/writer.rs    | 10 +++++++---
 tests/out/hlsl/access.hlsl | 10 +++++-----
 2 files changed, 12 insertions(+), 8 deletions(-)

diff --git a/src/back/hlsl/writer.rs b/src/back/hlsl/writer.rs
index 42e3060798..09cdeed48e 100644
--- a/src/back/hlsl/writer.rs
+++ b/src/back/hlsl/writer.rs
@@ -2085,14 +2085,18 @@ impl<'a, W: fmt::Write> super::Writer<'a, W> {
                         index: u32,
                     ) -> BackendResult {
                         match *resolved {
-                            TypeInner::Vector { .. } => {
+                            // We specifcally lift the ValuePointer to this case. While `[0]` is valid
+                            // HLSL for any vector behind a value pointer, FXC completely miscompiles
+                            // it and generates completely nonsensical DXBC.
+                            //
+                            // See https://github.com/gfx-rs/naga/issues/2095 for more details.
+                            TypeInner::Vector { .. } | TypeInner::ValuePointer { .. } => {
                                 // Write vector access as a swizzle
                                 write!(writer.out, ".{}", back::COMPONENTS[index as usize])?
                             }
                             TypeInner::Matrix { .. }
                             | TypeInner::Array { .. }
-                            | TypeInner::BindingArray { .. }
-                            | TypeInner::ValuePointer { .. } => write!(writer.out, "[{}]", index)?,
+                            | TypeInner::BindingArray { .. } => write!(writer.out, "[{}]", index)?,
                             TypeInner::Struct { .. } => {
                                 // This will never panic in case the type is a `Struct`, this is not true
                                 // for other types so we can only check while inside this match arm
diff --git a/tests/out/hlsl/access.hlsl b/tests/out/hlsl/access.hlsl
index 5510ec05bc..4402cfdf83 100644
--- a/tests/out/hlsl/access.hlsl
+++ b/tests/out/hlsl/access.hlsl
@@ -147,11 +147,11 @@ void test_matrix_within_struct_accesses()
     float2 unnamed_1 = GetMatmOnBaz(baz)[0];
     int _expr16 = idx;
     float2 unnamed_2 = GetMatmOnBaz(baz)[_expr16];
-    float unnamed_3 = GetMatmOnBaz(baz)[0][1];
+    float unnamed_3 = GetMatmOnBaz(baz)[0].y;
     int _expr28 = idx;
     float unnamed_4 = GetMatmOnBaz(baz)[0][_expr28];
     int _expr32 = idx;
-    float unnamed_5 = GetMatmOnBaz(baz)[_expr32][1];
+    float unnamed_5 = GetMatmOnBaz(baz)[_expr32].y;
     int _expr38 = idx;
     int _expr40 = idx;
     float unnamed_6 = GetMatmOnBaz(baz)[_expr38][_expr40];
@@ -191,11 +191,11 @@ void test_matrix_within_array_within_struct_accesses()
     float2 unnamed_9 = nested_mat_cx2_.am[0]._0;
     int _expr25 = idx_1;
     float2 unnamed_10 = __get_col_of_mat4x2(nested_mat_cx2_.am[0], _expr25);
-    float unnamed_11 = nested_mat_cx2_.am[0]._0[1];
+    float unnamed_11 = nested_mat_cx2_.am[0]._0.y;
     int _expr41 = idx_1;
     float unnamed_12 = nested_mat_cx2_.am[0]._0[_expr41];
     int _expr47 = idx_1;
-    float unnamed_13 = __get_col_of_mat4x2(nested_mat_cx2_.am[0], _expr47)[1];
+    float unnamed_13 = __get_col_of_mat4x2(nested_mat_cx2_.am[0], _expr47).y;
     int _expr55 = idx_1;
     int _expr57 = idx_1;
     float unnamed_14 = __get_col_of_mat4x2(nested_mat_cx2_.am[0], _expr55)[_expr57];
@@ -207,7 +207,7 @@ void test_matrix_within_array_within_struct_accesses()
     t_1.am[0]._0 = (9.0).xx;
     int _expr90 = idx_1;
     __set_col_of_mat4x2(t_1.am[0], _expr90, (90.0).xx);
-    t_1.am[0]._0[1] = 10.0;
+    t_1.am[0]._0.y = 10.0;
     int _expr107 = idx_1;
     t_1.am[0]._0[_expr107] = 20.0;
     int _expr113 = idx_1;