[Mesa-dev] [PATCH 1/3] glsl/lower_output_reads: fix geometry shader output handling with conditional emit

[Nicolai Hähnle]

From: Nicolai Hähnle <nicolai.haehnle at amd.com>

Consider a geometry shader that contains code like this:

   some_out = expr;

   if (cond) {
      ...
      EmitVertex();
   } else {
      ...
      EmitVertex();
   }

Both branches should see the correct value of some_out.

Since this is a rather subtle and rare case, I'm submitting a piglit test
for this as well.

GLSL says that the values of output variables are undefined after
EmitVertex(). With this change, the values will now be defined and
unmodified. This may reduce optimization opportunities in the probably
quite rare case where subsequent compiler passes cannot prove that the
value of the output variable is overwritten.

Cc: 13.0 <mesa-stable at lists.freedesktop.org>
---
 src/compiler/glsl/lower_output_reads.cpp | 1 -
 1 file changed, 1 deletion(-)

diff --git a/src/compiler/glsl/lower_output_reads.cpp b/src/compiler/glsl/lower_output_reads.cpp
index 732f4d3..8a375ac 100644
--- a/src/compiler/glsl/lower_output_reads.cpp
+++ b/src/compiler/glsl/lower_output_reads.cpp
@@ -150,21 +150,20 @@ ir_visitor_status
 output_read_remover::visit_leave(ir_return *ir)
 {
    hash_table_call_foreach(replacements, emit_return_copy, ir);
    return visit_continue;
 }
 
 ir_visitor_status
 output_read_remover::visit_leave(ir_emit_vertex *ir)
 {
    hash_table_call_foreach(replacements, emit_return_copy, ir);
-   _mesa_hash_table_clear(replacements, NULL);
    return visit_continue;
 }
 
 ir_visitor_status
 output_read_remover::visit_leave(ir_function_signature *sig)
 {
    if (strcmp(sig->function_name(), "main") != 0)
       return visit_continue;
 
    hash_table_call_foreach(replacements, emit_main_copy, sig);
-- 
2.7.4