glsl: add always_active_io attribute to ir_variable

The value will be set in separate-shader program when an input/output
must remains active. e.g. when deadcode removal isn't allowed because
it will create interface location/name-matching mismatch.

v3:
* Rename the attribute
* Use ir_variable directly instead of ir_variable_refcount_visitor
* Move the foreach IR code in the linker file

v4:
* Fix variable name in assert

v5 (by Timothy Arceri):
* Rename functions and reword comments
* Don't set always active on builtins

Signed-off-by: Gregory Hainaut <gregory.hainaut@gmail.com>
Reviewed-by: Timothy Arceri <timothy.arceri@collabora.com>
Reviewed-by: Tapani Pälli <tapani.palli@intel.com>
(cherry picked from commit 618612f867ed8140409796535314d9b9ed58440b)
Nominated-by: Timothy Arceri <timothy.arceri@collabora.com>

3 files changed, 82 insertions, 0 deletions

diff --git a/src/glsl/ir.cpp b/src/glsl/ir.cpp
index ca520f547a1..f989e9b6dff 100644
--- a/src/glsl/ir.cpp
+++ b/src/glsl/ir.cpp
@@ -1669,6 +1669,7 @@ ir_variable::ir_variable(const struct glsl_type *type, const char *name,
    this->data.pixel_center_integer = false;
    this->data.depth_layout = ir_depth_layout_none;
    this->data.used = false;
+   this->data.always_active_io = false;
    this->data.read_only = false;
    this->data.centroid = false;
    this->data.sample = false;
diff --git a/src/glsl/ir.h b/src/glsl/ir.h
index e1109eec1d3..bdc932ef538 100644
--- a/src/glsl/ir.h
+++ b/src/glsl/ir.h
@@ -659,6 +659,13 @@ public:
       unsigned assigned:1;
 
       /**
+       * When separate shader programs are enabled, only input/outputs between
+       * the stages of a multi-stage separate program can be safely removed
+       * from the shader interface. Other input/outputs must remains active.
+       */
+      unsigned always_active_io:1;
+
+      /**
        * Enum indicating how the variable was declared.  See
        * ir_var_declaration_type.
        *
diff --git a/src/glsl/linker.cpp b/src/glsl/linker.cpp
index 331d9a28007..57974f5d70e 100644
--- a/src/glsl/linker.cpp
+++ b/src/glsl/linker.cpp
@@ -3940,6 +3940,77 @@ split_ubos_and_ssbos(void *mem_ctx,
    assert(*num_ubos + *num_ssbos == num_blocks);
 }
 
+static void
+set_always_active_io(exec_list *ir, ir_variable_mode io_mode)
+{
+   assert(io_mode == ir_var_shader_in || io_mode == ir_var_shader_out);
+
+   foreach_in_list(ir_instruction, node, ir) {
+      ir_variable *const var = node->as_variable();
+
+      if (var == NULL || var->data.mode != io_mode)
+         continue;
+
+      /* Don't set always active on builtins that haven't been redeclared */
+      if (var->data.how_declared == ir_var_declared_implicitly)
+         continue;
+
+      var->data.always_active_io = true;
+   }
+}
+
+/**
+ * When separate shader programs are enabled, only input/outputs between
+ * the stages of a multi-stage separate program can be safely removed
+ * from the shader interface. Other inputs/outputs must remain active.
+ */
+static void
+disable_varying_optimizations_for_sso(struct gl_shader_program *prog)
+{
+   unsigned first, last;
+   assert(prog->SeparateShader);
+
+   first = MESA_SHADER_STAGES;
+   last = 0;
+
+   /* Determine first and last stage. Excluding the compute stage */
+   for (unsigned i = 0; i < MESA_SHADER_COMPUTE; i++) {
+      if (!prog->_LinkedShaders[i])
+         continue;
+      if (first == MESA_SHADER_STAGES)
+         first = i;
+      last = i;
+   }
+
+   if (first == MESA_SHADER_STAGES)
+      return;
+
+   for (unsigned stage = 0; stage < MESA_SHADER_STAGES; stage++) {
+      gl_shader *sh = prog->_LinkedShaders[stage];
+      if (!sh)
+         continue;
+
+      if (first == last) {
+         /* For a single shader program only allow inputs to the vertex shader
+          * and outputs from the fragment shader to be removed.
+          */
+         if (stage != MESA_SHADER_VERTEX)
+            set_always_active_io(sh->ir, ir_var_shader_in);
+         if (stage != MESA_SHADER_FRAGMENT)
+            set_always_active_io(sh->ir, ir_var_shader_out);
+      } else {
+         /* For multi-stage separate shader programs only allow inputs and
+          * outputs between the shader stages to be removed as well as inputs
+          * to the vertex shader and outputs from the fragment shader.
+          */
+         if (stage == first && stage != MESA_SHADER_VERTEX)
+            set_always_active_io(sh->ir, ir_var_shader_in);
+         else if (stage == last && stage != MESA_SHADER_FRAGMENT)
+            set_always_active_io(sh->ir, ir_var_shader_out);
+      }
+   }
+}
+
 void
 link_shaders(struct gl_context *ctx, struct gl_shader_program *prog)
 {
@@ -4199,6 +4270,9 @@ link_shaders(struct gl_context *ctx, struct gl_shader_program *prog)
       }
    }
 
+   if (prog->SeparateShader)
+      disable_varying_optimizations_for_sso(prog);
+
    if (!interstage_cross_validate_uniform_blocks(prog))
       goto done;