[Mesa-dev] [PATCH 44/59] i965/fs: add a pass for legalizing d2f

[Samuel Iglesias Gonsálvez]

From: Connor Abbott <cwabbott0 at gmail.com>

We need to do this late, in order to avoid partial writes during the
optimization loop.
---
 src/mesa/drivers/dri/i965/Makefile.sources     |  1 +
 src/mesa/drivers/dri/i965/brw_fs.cpp           |  5 ++
 src/mesa/drivers/dri/i965/brw_fs.h             |  1 +
 src/mesa/drivers/dri/i965/brw_fs_lower_d2f.cpp | 73 ++++++++++++++++++++++++++
 4 files changed, 80 insertions(+)
 create mode 100644 src/mesa/drivers/dri/i965/brw_fs_lower_d2f.cpp

diff --git a/src/mesa/drivers/dri/i965/Makefile.sources b/src/mesa/drivers/dri/i965/Makefile.sources
index 2b2a51d..47870f2 100644
--- a/src/mesa/drivers/dri/i965/Makefile.sources
+++ b/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 \
diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp
index 45afd1a..cac4c20 100644
--- a/src/mesa/drivers/dri/i965/brw_fs.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
@@ -5349,6 +5349,11 @@ 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);
 
diff --git a/src/mesa/drivers/dri/i965/brw_fs.h b/src/mesa/drivers/dri/i965/brw_fs.h
index 833061b..e57bc6b 100644
--- a/src/mesa/drivers/dri/i965/brw_fs.h
+++ b/src/mesa/drivers/dri/i965/brw_fs.h
@@ -173,6 +173,7 @@ 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();
diff --git a/src/mesa/drivers/dri/i965/brw_fs_lower_d2f.cpp b/src/mesa/drivers/dri/i965/brw_fs_lower_d2f.cpp
new file mode 100644
index 0000000..10ea2b2
--- /dev/null
+++ b/src/mesa/drivers/dri/i965/brw_fs_lower_d2f.cpp
@@ -0,0 +1,73 @@
+/*
+ * 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(BRW_REGISTER_TYPE_F, 2);
+      ibld.MOV(stride(temp, 2), inst->src[0]);
+      ibld.MOV(dst, stride(temp, 2));
+
+      inst->remove(block);
+      progress = true;
+   }
+
+   if (progress)
+      invalidate_live_intervals();
+
+   return progress;
+}
-- 
2.5.0