nir: Pass through fb_fetch_output and OutputsRead from GLSL IR.

The NIR representation of framebuffer fetch is the same as the GLSL
IR's until interface variables are lowered away, at which point it
will be translated to load output intrinsics.  The GLSL-to-NIR pass
just needs to copy the bits over to the NIR program.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/compiler/glsl/glsl_to_nir.cpp

@@ -154,6 +154,7 @@ glsl_to_nir(const struct gl_shader_program *shader_prog,
    shader->info.inputs_read = sh->Program->InputsRead;
    shader->info.double_inputs_read = sh->Program->DoubleInputsRead;
    shader->info.outputs_written = sh->Program->OutputsWritten;
+   shader->info.outputs_read = sh->Program->OutputsRead;
    shader->info.patch_inputs_read = sh->Program->PatchInputsRead;
    shader->info.patch_outputs_written = sh->Program->PatchOutputsWritten;
    shader->info.system_values_read = sh->Program->SystemValuesRead;
@@ -406,6 +407,7 @@ nir_visitor::visit(ir_variable *ir)
    var->data.image.restrict_flag = ir->data.image_restrict;
    var->data.image.format = ir->data.image_format;
    var->data.max_array_access = ir->data.max_array_access;
+   var->data.fb_fetch_output = ir->data.fb_fetch_output;
 
    var->num_state_slots = ir->get_num_state_slots();
    if (var->num_state_slots > 0) {

src/compiler/nir/nir.h

@@ -226,6 +226,13 @@ typedef struct nir_variable {
        */
       unsigned location_frac:2;
 
+      /**
+       * Whether this is a fragment shader output implicitly initialized with
+       * the previous contents of the specified render target at the
+       * framebuffer location corresponding to this shader invocation.
+       */
+      unsigned fb_fetch_output:1;
+
       /**
        * \brief Layout qualifier for gl_FragDepth.
        *
@@ -1776,6 +1783,8 @@ typedef struct nir_shader_info {
    uint64_t double_inputs_read;
    /* Which outputs are actually written */
    uint64_t outputs_written;
+   /* Which outputs are actually read */
+   uint64_t outputs_read;
    /* Which system values are actually read */
    uint64_t system_values_read;