i965/fs: Clear result before visiting shadow comparitor and LOD info.

Commit 53c89c67f3 ("i965: Avoid generating
MOVs for assignments of expressions.") added the line "this->result =
reg_undef" all over the code.  Unfortunately, since Eric developed his
patch before I landed Ivybridge support, he missed adding it to
fs_visitor::emit_texture_gen7() after rebasing.

Furthermore, since I developed TXD support before Eric's patch, I
neglected to add it to the gradient handling when I rebased.

Neglecting to set this causes the visitor to use this->result as storage
rather than generating a new temporary.  These missing statements
resulted in the same register being used to store several different
values.

Fixes the following piglit tests on Ivybridge:
- glsl-fs-shadow2dproj.shader_test
- glsl-fs-shadow2dproj-bias.shader_test

NOTE: This is a candidate for the 7.11 branch.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Eric Anholt <eric@anholt.net>

src/mesa/drivers/dri/i965/brw_fs_visitor.cpp

       /* gen4's SIMD8 sampler always has the slots for u,v,r present. */
       mlen += 3;
    } else if (ir->op == ir_txd) {
+      this->result = reg_undef;
       ir->lod_info.grad.dPdx->accept(this);
       fs_reg dPdx = this->result;
 
+      this->result = reg_undef;
       ir->lod_info.grad.dPdy->accept(this);
       fs_reg dPdy = this->result;
 
       inst = emit(FS_OPCODE_TXL, dst);
       break;
    case ir_txd: {
+      this->result = reg_undef;
       ir->lod_info.grad.dPdx->accept(this);
       fs_reg dPdx = this->result;
 
+      this->result = reg_undef;
       ir->lod_info.grad.dPdy->accept(this);
       fs_reg dPdy = this->result;
 
    }
 
    if (ir->shadow_comparitor && ir->op != ir_txd) {
+      this->result = reg_undef;
       ir->shadow_comparitor->accept(this);
       emit(BRW_OPCODE_MOV, fs_reg(MRF, base_mrf + mlen), this->result);
       mlen += reg_width;
    case ir_tex:
       break;
    case ir_txb:
+      this->result = reg_undef;
       ir->lod_info.bias->accept(this);
       emit(BRW_OPCODE_MOV, fs_reg(MRF, base_mrf + mlen), this->result);
       mlen += reg_width;
       break;
    case ir_txl:
+      this->result = reg_undef;
       ir->lod_info.lod->accept(this);
       emit(BRW_OPCODE_MOV, fs_reg(MRF, base_mrf + mlen), this->result);
       mlen += reg_width;
       if (c->dispatch_width == 16)
 	 fail("Gen7 does not support sample_d/sample_d_c in SIMD16 mode.");
 
+      this->result = reg_undef;
       ir->lod_info.grad.dPdx->accept(this);
       fs_reg dPdx = this->result;
 
+      this->result = reg_undef;
       ir->lod_info.grad.dPdy->accept(this);
       fs_reg dPdy = this->result;
 
       if (hw_compare_supported) {
 	 inst->shadow_compare = true;
       } else {
+	 this->result = reg_undef;
 	 ir->shadow_comparitor->accept(this);
 	 fs_reg ref = this->result;