i965/fs: add a pass for legalizing d2f

We need to do this late, in order to avoid partial writes during the
optimization loop.

v2: Use subscript() instead of stride().

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/mesa/drivers/dri/i965/Makefile.sources

@@ -26,6 +26,7 @@ i965_compiler_FILES = \
 	brw_fs.h \
 	brw_fs_live_variables.cpp \
 	brw_fs_live_variables.h \
+	brw_fs_lower_d2f.cpp \
 	brw_fs_lower_pack.cpp \
 	brw_fs_nir.cpp \
 	brw_fs_reg_allocate.cpp \

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

@@ -5359,6 +5359,11 @@ fs_visitor::optimize()
       OPT(dead_code_eliminate);
    }
 
+   if (OPT(lower_d2f)) {
+      OPT(opt_copy_propagate);
+      OPT(dead_code_eliminate);
+   }
+
    OPT(opt_combine_constants);
    OPT(lower_integer_multiplication);
 

src/mesa/drivers/dri/i965/brw_fs.h

@@ -174,6 +174,7 @@ public:
    void lower_uniform_pull_constant_loads();
    bool lower_load_payload();
    bool lower_pack();
+   bool lower_d2f();
    bool lower_logical_sends();
    bool lower_integer_multiplication();
    bool lower_minmax();

src/mesa/drivers/dri/i965/brw_fs_lower_d2f.cpp

@@ -0,0 +1,74 @@
+/*
+ * Copyright © 2015 Connor Abbott
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ */
+
+#include "brw_fs.h"
+#include "brw_cfg.h"
+#include "brw_fs_builder.h"
+
+using namespace brw;
+
+bool
+fs_visitor::lower_d2f()
+{
+   bool progress = false;
+
+   foreach_block_and_inst_safe(block, fs_inst, inst, cfg) {
+      if (inst->opcode != BRW_OPCODE_MOV)
+         continue;
+
+      if (inst->dst.type != BRW_REGISTER_TYPE_F)
+         continue;
+
+      if (inst->src[0].type != BRW_REGISTER_TYPE_DF)
+         continue;
+
+      assert(inst->dst.file == VGRF);
+      assert(inst->saturate == false);
+      fs_reg dst = inst->dst;
+
+      const fs_builder ibld(this, block, inst);
+
+      /* From the Broadwell PRM, 3D Media GPGPU, "Double Precision Float to
+       * Single Precision Float":
+       *
+       *    The upper Dword of every Qword will be written with undefined
+       *    value when converting DF to F.
+       *
+       * So we need to allocate a temporary that's two registers, and then do
+       * a strided MOV to get the lower DWord of every Qword that has the
+       * result.
+       */
+      fs_reg temp = ibld.vgrf(inst->src[0].type, 1);
+      fs_reg strided_temp = subscript(temp, inst->dst.type, 0);
+      ibld.MOV(strided_temp, inst->src[0]);
+      ibld.MOV(dst, strided_temp);
+
+      inst->remove(block);
+      progress = true;
+   }
+
+   if (progress)
+      invalidate_live_intervals();
+
+   return progress;
+}