[Mesa-dev] [PATCH] glsl: fix array assignments of a swizzled vector

[Ilia Mirkin]

This happens in situations where we might do

  vec.wzyx[i] = ...

The swizzle would get effectively ignored because of the interaction
between how ir_assignment->set_lhs works and overwriting the write_mask.

Fixes the following WebGL test:

https://www.khronos.org/registry/webgl/sdk/tests/conformance2/glsl3/vector-dynamic-indexing-swizzled-lvalue.html

Signed-off-by: Ilia Mirkin <imirkin at alum.mit.edu>
Cc: mesa-stable at lists.freedesktop.org
---
 src/compiler/glsl/lower_vector_derefs.cpp | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/src/compiler/glsl/lower_vector_derefs.cpp b/src/compiler/glsl/lower_vector_derefs.cpp
index 7583d1fdd3e..af046966491 100644
--- a/src/compiler/glsl/lower_vector_derefs.cpp
+++ b/src/compiler/glsl/lower_vector_derefs.cpp
@@ -59,21 +59,27 @@ vector_deref_visitor::visit_enter(ir_assignment *ir)
    if (!deref->array->type->is_vector())
       return ir_rvalue_enter_visitor::visit_enter(ir);
 
-   ir_dereference *const new_lhs = (ir_dereference *) deref->array;
-   ir->set_lhs(new_lhs);
+   ir_rvalue *const new_lhs = deref->array;
 
    void *mem_ctx = ralloc_parent(ir);
    ir_constant *old_index_constant =
       deref->array_index->constant_expression_value(mem_ctx);
    if (!old_index_constant) {
+      ir->set_lhs(new_lhs);
       ir->rhs = new(mem_ctx) ir_expression(ir_triop_vector_insert,
                                            new_lhs->type,
                                            new_lhs->clone(mem_ctx, NULL),
                                            ir->rhs,
                                            deref->array_index);
       ir->write_mask = (1 << new_lhs->type->vector_elements) - 1;
+   } else if (new_lhs->ir_type != ir_type_swizzle) {
+      ir->set_lhs(new_lhs);
+      ir->write_mask = 1 << old_index_constant->get_uint_component(0);
    } else {
-      ir->write_mask = 1 << old_index_constant->get_int_component(0);
+      // If there "new" lhs is a swizzle, use the set_lhs helper to instead
+      // swizzle the rhs.
+      unsigned component[1] = { old_index_constant->get_uint_component(0) };
+      ir->set_lhs(new(mem_ctx) ir_swizzle(new_lhs, component, 1));
    }
 
    return ir_rvalue_enter_visitor::visit_enter(ir);
-- 
2.16.4