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@itsqueeze.com>

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 a26253998e024464898cca3721176477775b1c41..89244266602cda5aab88c6364c9ef10d2a40bcf0 100644 (file)
--- 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),