i965: Add support for live variable analysis using dataflow analysis.

2012-04-11 13:12:33 -07:00
parent 080b125c64
commit 0d6c96a5c3
3 changed files with 245 additions and 0 deletions
@@ -116,6 +116,7 @@ i965_CXX_FILES := \
 	brw_fs.cpp \
 	brw_fs_cfg.cpp \
 	brw_fs_emit.cpp \
+	brw_fs_live_variables.cpp \
 	brw_fs_visitor.cpp \
 	brw_fs_channel_expressions.cpp \
 	brw_fs_reg_allocate.cpp \
@@ -0,0 +1,158 @@
+/*
+ * Copyright © 2012 Intel Corporation
+ *
+ * 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.
+ *
+ * Authors:
+ *    Eric Anholt <eric@anholt.net>
+ *
+ */
+
+#include "brw_fs_cfg.h"
+#include "brw_fs_live_variables.h"
+
+using namespace brw;
+
+/** @file brw_fs_live_variables.cpp
+ *
+ * Support for computing at the basic block level which variables
+ * (virtual GRFs in our case) are live at entry and exit.
+ *
+ * See Muchnik's Advanced Compiler Design and Implementation, section
+ * 14.1 (p444).
+ */
+
+/**
+ * Sets up the use[] and def[] arrays.
+ *
+ * The basic-block-level live variable analysis needs to know which
+ * variables get used before they're completely defined, and which
+ * variables are completely defined before they're used.
+ */
+void
+fs_live_variables::setup_def_use()
+{
+   int ip = 0;
+
+   for (int b = 0; b < cfg->num_blocks; b++) {
+      fs_bblock *block = cfg->blocks[b];
+
+      assert(ip == block->start_ip);
+      if (b > 0)
+	 assert(cfg->blocks[b - 1]->end_ip == ip - 1);
+
+      for (fs_inst *inst = block->start;
+	   inst != block->end->next;
+	   inst = (fs_inst *)inst->next) {
+
+	 /* Set use[] for this instruction */
+	 for (unsigned int i = 0; i < 3; i++) {
+	    if (inst->src[i].file == GRF) {
+	       int reg = inst->src[i].reg;
+
+	       if (!bd[b].def[reg])
+		  bd[b].use[reg] = true;
+	    }
+	 }
+
+	 /* Check for unconditional writes to whole registers. These
+	  * are the things that screen off preceding definitions of a
+	  * variable, and thus qualify for being in def[].
+	  */
+	 if (inst->dst.file == GRF &&
+	     inst->regs_written() == v->virtual_grf_sizes[inst->dst.reg] &&
+	     !inst->predicated &&
+	     !inst->force_uncompressed &&
+	     !inst->force_sechalf) {
+	    int reg = inst->dst.reg;
+	    if (!bd[b].use[reg])
+	       bd[b].def[reg] = true;
+	 }
+
+	 ip++;
+      }
+   }
+}
+
+/**
+ * The algorithm incrementally sets bits in liveout and livein,
+ * propagating it through control flow.  It will eventually terminate
+ * because it only ever adds bits, and stops when no bits are added in
+ * a pass.
+ */
+void
+fs_live_variables::compute_live_variables()
+{
+   bool cont = true;
+
+   while (cont) {
+      cont = false;
+
+      for (int b = 0; b < cfg->num_blocks; b++) {
+	 /* Update livein */
+	 for (int i = 0; i < num_vars; i++) {
+	    if (bd[b].use[i] || (bd[b].liveout[i] && !bd[b].def[i])) {
+	       if (!bd[b].livein[i]) {
+		  bd[b].livein[i] = true;
+		  cont = true;
+	       }
+	    }
+	 }
+
+	 /* Update liveout */
+	 foreach_list(block_node, &cfg->blocks[b]->children) {
+	    fs_bblock_link *link = (fs_bblock_link *)block_node;
+	    fs_bblock *block = link->block;
+
+	    for (int i = 0; i < num_vars; i++) {
+	       if (bd[block->block_num].livein[i] && !bd[b].liveout[i]) {
+		  bd[b].liveout[i] = true;
+		  cont = true;
+	       }
+	    }
+	 }
+      }
+   }
+}
+
+fs_live_variables::fs_live_variables(fs_visitor *v, fs_cfg *cfg)
+   : v(v), cfg(cfg)
+{
+   mem_ctx = ralloc_context(cfg->mem_ctx);
+
+   num_vars = v->virtual_grf_next;
+   bd = rzalloc_array(mem_ctx, struct block_data, cfg->num_blocks);
+   vars = rzalloc_array(mem_ctx, struct var, num_vars);
+
+   for (int i = 0; i < cfg->num_blocks; i++) {
+      bd[i].def = rzalloc_array(mem_ctx, bool, num_vars);
+      bd[i].use = rzalloc_array(mem_ctx, bool, num_vars);
+      bd[i].livein = rzalloc_array(mem_ctx, bool, num_vars);
+      bd[i].liveout = rzalloc_array(mem_ctx, bool, num_vars);
+   }
+
+   setup_def_use();
+   compute_live_variables();
+}
+
+fs_live_variables::~fs_live_variables()
+{
+   ralloc_free(mem_ctx);
+}
@@ -0,0 +1,86 @@
+/*
+ * Copyright © 2012 Intel Corporation
+ *
+ * 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.
+ *
+ * Authors:
+ *    Eric Anholt <eric@anholt.net>
+ *
+ */
+
+#include "brw_fs.h"
+
+namespace brw {
+
+struct block_data {
+   /**
+    * Which variables are defined before being used in the block.
+    *
+    * Note that for our purposes, "defined" means unconditionally, completely
+    * defined.
+    */
+   bool *def;
+
+   /**
+    * Which variables are used before being defined in the block.
+    */
+   bool *use;
+
+   /** Which defs reach the entry point of the block. */
+   bool *livein;
+
+   /** Which defs reach the exit point of the block. */
+   bool *liveout;
+};
+
+class fs_live_variables {
+public:
+   static void* operator new(size_t size, void *ctx)
+   {
+      void *node;
+
+      node = rzalloc_size(ctx, size);
+      assert(node != NULL);
+
+      return node;
+   }
+
+   fs_live_variables(fs_visitor *v, fs_cfg *cfg);
+   ~fs_live_variables();
+
+   void setup_def_use();
+   void compute_live_variables();
+
+   fs_visitor *v;
+   fs_cfg *cfg;
+   void *mem_ctx;
+
+   struct var {
+      int blocknum;
+      int instnum;
+      fs_inst *inst;
+   } *vars;
+   int num_vars;
+
+   /** Per-basic-block information on live variables */
+   struct block_data *bd;
+};
+
+} /* namespace brw */