Mesa (master): glsl: fix interpolateAtXxx(some_vec[idx], ...) with dynamic idx

[Nicolai Hähnle]

Module: Mesa
Branch: master
Commit: ca63a5ed3e9efb2bd645b425f7393089f4e132a6
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=ca63a5ed3e9efb2bd645b425f7393089f4e132a6

Author: Nicolai Hähnle <nicolai.haehnle at amd.com>
Date:   Tue Aug  1 12:44:34 2017 +0200

glsl: fix interpolateAtXxx(some_vec[idx], ...) with dynamic idx

The dynamic index of a vector (not array!) is lowered to a sequence of
conditional assignments. However, the interpolate_at_* expressions
require that the interpolant is an l-value of a shader input.

So instead of doing conditional assignments of parts of the shader input
and then interpolating that (which is nonsensical), we interpolate the
entire shader input and then do conditional assignments of the interpolated
result.

Reviewed-by: Timothy Arceri <tarceri at itsqueeze.com>

---

 .../glsl/lower_vec_index_to_cond_assign.cpp        | 31 +++++++++++++++++++++-
 1 file changed, 30 insertions(+), 1 deletion(-)

diff --git a/src/compiler/glsl/lower_vec_index_to_cond_assign.cpp b/src/compiler/glsl/lower_vec_index_to_cond_assign.cpp
index a26253998e..8924426660 100644
--- a/src/compiler/glsl/lower_vec_index_to_cond_assign.cpp
+++ b/src/compiler/glsl/lower_vec_index_to_cond_assign.cpp
@@ -128,7 +128,36 @@ ir_vec_index_to_cond_assign_visitor::convert_vector_extract_to_cond_assign(ir_rv
 {
    ir_expression *const expr = ir->as_expression();
 
-   if (expr == NULL || expr->operation != ir_binop_vector_extract)
+   if (expr == NULL)
+      return ir;
+
+   if (expr->operation == ir_unop_interpolate_at_centroid ||
+       expr->operation == ir_binop_interpolate_at_offset ||
+       expr->operation == ir_binop_interpolate_at_sample) {
+      /* Lower interpolateAtXxx(some_vec[idx], ...) to
+       * interpolateAtXxx(some_vec, ...)[idx] before lowering to conditional
+       * assignments, to maintain the rule that the interpolant is an l-value
+       * referring to a (part of a) shader input.
+       *
+       * This is required when idx is dynamic (otherwise it gets lowered to
+       * a swizzle).
+       */
+      ir_expression *const interpolant = expr->operands[0]->as_expression();
+      if (!interpolant || interpolant->operation != ir_binop_vector_extract)
+         return ir;
+
+      ir_rvalue *vec_input = interpolant->operands[0];
+      ir_expression *const vec_interpolate =
+         new(base_ir) ir_expression(expr->operation, vec_input->type,
+                                    vec_input, expr->operands[1]);
+
+      return convert_vec_index_to_cond_assign(ralloc_parent(ir),
+                                              vec_interpolate,
+                                              interpolant->operands[1],
+                                              ir->type);
+   }
+
+   if (expr->operation != ir_binop_vector_extract)
       return ir;
 
    return convert_vec_index_to_cond_assign(ralloc_parent(ir),