st/glsl_to_tgsi: fix conditional assignments to packed shader outputs

Overriding the default (no-op) swizzle is clearly counter-productive,
since the whole point is putting the destination register as one of
the source operands so that it remains unmodified when the assignment
condition is false.

Fragment depth and stencil outputs are a special case due to how their
source swizzles are manipulated in translate_src when compiling to
TGSI.

Fixes dEQP-GLES2.functional.shaders.conditionals.if.*_vertex
Cc: [email protected]
Reviewed-by: Marek Olšák <[email protected]>
Tested-by: Dieter Nützel <[email protected]>

1 files changed, 9 insertions, 1 deletions

diff --git a/src/mesa/state_tracker/st_glsl_to_tgsi.cpp b/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
index f4870a1c606..0daf5a14285 100644
--- a/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
+++ b/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
@@ -2897,7 +2897,15 @@ glsl_to_tgsi_visitor::emit_block_mov(ir_assignment *ir, const struct glsl_type *
    r->type = type->base_type;
    if (cond) {
       st_src_reg l_src = st_src_reg(*l);
-      l_src.swizzle = swizzle_for_size(type->vector_elements);
+
+      if (l_src.file == PROGRAM_OUTPUT &&
+          this->prog->Target == GL_FRAGMENT_PROGRAM_ARB &&
+          (l_src.index == FRAG_RESULT_DEPTH || l_src.index == FRAG_RESULT_STENCIL)) {
+         /* This is a special case because the source swizzles will be shifted
+          * later to account for the difference between GLSL (where they're
+          * plain floats) and TGSI (where they're Z and Y components). */
+         l_src.swizzle = SWIZZLE_XXXX;
+      }
 
       if (native_integers) {
          emit_asm(ir, TGSI_OPCODE_UCMP, *l, *cond,