mesa/st: Don't copy propagate from swizzles.

Do not propagate a copy if source and destination are identical.

Otherwise code like

MOV TEMP[0].xyzw, TEMP[0].wzyx
MOV TEMP[1].xyzw, TEMP[0].xyzw

is changed to

MOV TEMP[0].xyzw, TEMP[0].wzyx
MOV TEMP[1].xyzw, TEMP[0].wzyx

This fixes Piglit test shaders/glsl-copy-propagation-self-2 for gallium drivers.

NOTE: This is a candidate for the stable branches.
Signed-off-by: Fabian Bieler <fabianbieler@fastmail.fm>
Reviewed-by: Brian Paul <brianp@vmware.com>

src/mesa/state_tracker/st_glsl_to_tgsi.cpp

@@ -3552,6 +3552,8 @@ glsl_to_tgsi_visitor::copy_propagate(void)
       /* If this is a copy, add it to the ACP. */
       if (inst->op == TGSI_OPCODE_MOV &&
           inst->dst.file == PROGRAM_TEMPORARY &&
+          !(inst->dst.file == inst->src[0].file &&
+             inst->dst.index == inst->src[0].index) &&
           !inst->dst.reladdr &&
           !inst->saturate &&
           !inst->src[0].reladdr &&