mesa: Add channel-wise copy propagation to ir_to_mesa.

This catches more opportunities than the prog_optimize.c code on
openarena's fixed function shaders turned to GLSL, mostly due to
looking at multiple source instructions for copy propagation
opportunities.  It should also be much more CPU efficient than
prog_optimize.c's code.

diff --git a/src/mesa/program/ir_to_mesa.cpp b/src/mesa/program/ir_to_mesa.cpp
index c601ef6..0d40b09 100644 (file)
--- a/src/mesa/program/ir_to_mesa.cpp
+++ b/src/mesa/program/ir_to_mesa.cpp
@@ -295,6 +295,8 @@ public:
 
    bool process_move_condition(ir_rvalue *ir);
 
+   void copy_propagate(void);
+
    void *mem_ctx;
 };
 
@@ -2616,6 +2618,131 @@ set_uniform_initializers(struct gl_context *ctx,
    talloc_free(mem_ctx);
 }
 
+/*
+ * On a basic block basis, tracks available PROGRAM_TEMPORARY register
+ * channels for copy propagation and updates following instructions to
+ * use the original versions.
+ *
+ * The ir_to_mesa_visitor lazily produces code assuming that this pass
+ * will occur.  As an example, a TXP production before this pass:
+ *
+ * 0: MOV TEMP[1], INPUT[4].xyyy;
+ * 1: MOV TEMP[1].w, INPUT[4].wwww;
+ * 2: TXP TEMP[2], TEMP[1], texture[0], 2D;
+ *
+ * and after:
+ *
+ * 0: MOV TEMP[1], INPUT[4].xyyy;
+ * 1: MOV TEMP[1].w, INPUT[4].wwww;
+ * 2: TXP TEMP[2], INPUT[4].xyyw, texture[0], 2D;
+ *
+ * which allows for dead code elimination on TEMP[1]'s writes.
+ */
+void
+ir_to_mesa_visitor::copy_propagate(void)
+{
+   ir_to_mesa_instruction *acp[this->next_temp * 4];
+
+   memset(&acp, 0, sizeof(acp));
+
+   foreach_iter(exec_list_iterator, iter, this->instructions) {
+      ir_to_mesa_instruction *inst = (ir_to_mesa_instruction *)iter.get();
+
+      /* First, do any copy propagation possible into the src regs. */
+      for (int r = 0; r < 3; r++) {
+        ir_to_mesa_instruction *first = NULL;
+        bool good = true;
+        int acp_base = inst->src_reg[r].index * 4;
+
+        if (inst->src_reg[r].file != PROGRAM_TEMPORARY ||
+            inst->src_reg[r].reladdr)
+           continue;
+
+        /* See if we can find entries in the ACP consisting of MOVs
+         * from the same src register for all the swizzled channels
+         * of this src register reference.
+         */
+        for (int i = 0; i < 4; i++) {
+           int src_chan = GET_SWZ(inst->src_reg[r].swizzle, i);
+           ir_to_mesa_instruction *copy_chan = acp[acp_base + src_chan];
+
+           if (!copy_chan) {
+              good = false;
+              break;
+           }
+
+           if (!first) {
+              first = copy_chan;
+           } else {
+              if (first->src_reg[0].file != copy_chan->src_reg[0].file ||
+                  first->src_reg[0].index != copy_chan->src_reg[0].index) {
+                 good = false;
+                 break;
+              }
+           }
+        }
+
+        if (good) {
+           /* We've now validated that we can copy-propagate to
+            * replace this src register reference.  Do it.
+            */
+           inst->src_reg[r].file = first->src_reg[0].file;
+           inst->src_reg[r].index = first->src_reg[0].index;
+
+           int swizzle = 0;
+           for (int i = 0; i < 4; i++) {
+              int src_chan = GET_SWZ(inst->src_reg[r].swizzle, i);
+              ir_to_mesa_instruction *copy_inst = acp[acp_base + src_chan];
+              swizzle |= (GET_SWZ(copy_inst->src_reg[0].swizzle, src_chan) <<
+                          (3 * i));
+           }
+           inst->src_reg[r].swizzle = swizzle;
+        }
+      }
+
+      switch (inst->op) {
+      case OPCODE_BGNLOOP:
+      case OPCODE_ENDLOOP:
+      case OPCODE_ELSE:
+      case OPCODE_ENDIF:
+        /* End of a basic block, clear the ACP entirely. */
+        memset(&acp, 0, sizeof(acp));
+        break;
+
+      default:
+        /* Continuing the block, clear any written channels from
+         * the ACP.
+         */
+        if (inst->dst_reg.file == PROGRAM_TEMPORARY) {
+           if (inst->dst_reg.reladdr) {
+              memset(&acp, 0, sizeof(acp));
+           } else {
+              for (int i = 0; i < 4; i++) {
+                 if (inst->dst_reg.writemask & (1 << i)) {
+                    acp[4 * inst->dst_reg.index + i] = NULL;
+                 }
+              }
+           }
+        }
+        break;
+      }
+
+      /* If this is a copy, add it to the ACP. */
+      if (inst->op == OPCODE_MOV &&
+         inst->dst_reg.file == PROGRAM_TEMPORARY &&
+         !inst->dst_reg.reladdr &&
+         !inst->saturate &&
+         !inst->src_reg[0].reladdr &&
+         !inst->src_reg[0].negate) {
+        for (int i = 0; i < 4; i++) {
+           if (inst->dst_reg.writemask & (1 << i)) {
+              acp[4 * inst->dst_reg.index + i] = inst;
+           }
+        }
+      }
+   }
+}
+
 
 /**
  * Convert a shader's GLSL IR into a Mesa gl_program.
@@ -2715,6 +2842,8 @@ get_mesa_program(struct gl_context *ctx,
    mesa_instruction_annotation = talloc_array(v.mem_ctx, ir_instruction *,
                                              num_instructions);
 
+   v.copy_propagate();
+
    /* Convert ir_mesa_instructions into prog_instructions.
     */
    mesa_inst = mesa_instructions;