[PATCH v7 2/2] vkd3d-shader/hlsl: Avoid infinite loop in copy propagation.

[Giovanni Mascellani]

From: Giovanni Mascellani

Co-authored-by: Francisco Casas

Because copy_propagation_transform_object_load() replaces a deref
instead of an instruction, it is currently prone to two problems:

1- It can replace a deref with the same deref, returning true every
time and getting the compilation stuck in an endless loop of
copy-propagation iterations.

2- When performed multiple times in the same deref, the second time it
can replace the deref with a deref from a temp that is only valid in
another point of the program execution, resulting in an incorrect value.

This patch preempts this by avoiding propagating object loads when the
variable is a real object (i.e., a uniform variable) which cannot have a
replacement.
---
 libs/vkd3d-shader/hlsl_codegen.c    |  6 +++++
 tests/object-references.shader_test | 39 ++++++++++++++++++++++++++++-
 2 files changed, 44 insertions(+), 1 deletion(-)

diff --git a/libs/vkd3d-shader/hlsl_codegen.c b/libs/vkd3d-shader/hlsl_codegen.c
index 5e7cfff4..fa96ca4b 100644
--- a/libs/vkd3d-shader/hlsl_codegen.c
+++ b/libs/vkd3d-shader/hlsl_codegen.c
@@ -927,6 +927,12 @@ static bool copy_propagation_transform_object_load(struct hlsl_ctx *ctx,
     /* Only HLSL_IR_LOAD can produce an object. */
     load = hlsl_ir_load(value->node);

+    if (!load->src.var->is_uniform)
+    {
+        TRACE("Ignoring load from non-uniform object variable %s\n", load->src.var->name);
+        return false;
+    }
+
     hlsl_cleanup_deref(deref);
     hlsl_copy_deref(ctx, deref, &load->src);

diff --git a/tests/object-references.shader_test b/tests/object-references.shader_test
index 0c203d5a..bc74ccd4 100644
--- a/tests/object-references.shader_test
+++ b/tests/object-references.shader_test
@@ -1,3 +1,15 @@
+[pixel shader fail]
+sampler sam;
+
+float4 main() : sv_target
+{
+    Texture2D tex;
+
+    tex = tex; // Uninitialized assignment to self.
+    return tex.Sample(sam, float2(0, 0));
+}
+
+
 [require]
 shader model >= 4.0

@@ -35,7 +47,7 @@ float4 main() : sv_target

[test]
 draw quad
-todo probe all rgba (77.77, 77.77, 77.77, 77.77)
+probe all rgba (77.77, 77.77, 77.77, 77.77)

[texture 0]
@@ -201,3 +213,28 @@ float4 main(Texture2D tex2) : sv_target
     tex2 = tex1;
     return tex2.Load(int3(0, 0, 0));
 }
+
+
+[require]
+shader model >= 5.0
+
+
+[texture 0]
+size (1, 1)
+1.0 2.0 3.0 4.0
+
+[pixel shader todo]
+struct apple {
+    Texture2D tex;
+    float4 fo : COLOR;
+};
+
+float4 main(struct apple input) : sv_target
+{
+    input.tex = input.tex; // Assignment to self.
+    return input.tex.Load(int3(0, 0, 0));
+}
+
+[test]
+todo draw quad
+todo probe (0, 0) rgba (1.0, 2.0, 3.0, 4.0)