i965/vec4: Don't set header_present if texel offsets are all 0.

In theory, a shader might use textureOffset() but set all the texel
offsets to zero.  In that case, we don't actually need to set up the
message header - zero is the implicit default.

By moving the texture_offset setup before the header_present setup, we
can easily only set header_present when there are non-zero texel offset
values.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Chris Forbes <chrisf@ijw.co.nz>

diff --git a/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp b/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
index 15a6cbd..daf46b6 100644 (file)
--- a/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
+++ b/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
@@ -2363,10 +2363,16 @@ vec4_visitor::visit(ir_texture *ir)
       assert(!"Unrecognized tex op");
    }
 
-   bool use_texture_offset = ir->offset != NULL && ir->op != ir_txf;
+   if (ir->offset != NULL && ir->op != ir_txf)
+      inst->texture_offset = brw_texture_offset(ctx, ir->offset->as_constant());
+
+   /* Stuff the channel select bits in the top of the texture offset */
+   if (ir->op == ir_tg4)
+      inst->texture_offset |= gather_channel(ir, sampler) << 16;
 
    /* Texel offsets go in the message header; Gen4 also requires headers. */
-   inst->header_present = use_texture_offset || brw->gen < 5 || ir->op == ir_tg4;
+   inst->header_present =
+      brw->gen < 5 || inst->texture_offset != 0 || ir->op == ir_tg4;
    inst->base_mrf = 2;
    inst->mlen = inst->header_present + 1; /* always at least one */
    inst->sampler = sampler;
@@ -2374,13 +2380,6 @@ vec4_visitor::visit(ir_texture *ir)
    inst->dst.writemask = WRITEMASK_XYZW;
    inst->shadow_compare = ir->shadow_comparitor != NULL;
 
-   if (use_texture_offset)
-      inst->texture_offset = brw_texture_offset(ctx, ir->offset->as_constant());
-
-   /* Stuff the channel select bits in the top of the texture offset */
-   if (ir->op == ir_tg4)
-      inst->texture_offset |= gather_channel(ir, sampler)<<16;
-
    /* MRF for the first parameter */
    int param_base = inst->base_mrf + inst->header_present;