i965/fs: Copy propagate partial reads.

This commit reworks copy propagation a bit to support propagating the
copying of partial registers.  This comes up every time we have pull
constants because we do a pull constant read immediately followed by a move
to splat the one component of the out to 8 or 16-wide.  This allows us to
eliminate the copy and simply use the one component of the register.

Shader DB results:

total instructions in shared programs: 5044937 -> 5044428 (-0.01%)
instructions in affected programs:     66112 -> 65603 (-0.77%)
GAINED:                                0
LOST:                                  0

Signed-off-by: Jason Ekstrand <jason.ekstrand@intel.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>

1 files changed, 63 insertions, 20 deletions

diff --git a/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp b/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp
index da208dc..bd502c4 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp
@@ -277,24 +277,30 @@ is_logic_op(enum opcode opcode)
 bool
 fs_visitor::try_copy_propagate(fs_inst *inst, int arg, acp_entry *entry)
 {
+   if (inst->src[arg].file != GRF)
+      return false;
+
    if (entry->src.file == IMM)
       return false;
+   assert(entry->src.file == GRF || entry->src.file == UNIFORM);
 
    if (entry->opcode == SHADER_OPCODE_LOAD_PAYLOAD &&
        inst->opcode == SHADER_OPCODE_LOAD_PAYLOAD)
       return false;
 
-   /* Bail if inst is reading more than entry is writing. */
-   if ((inst->regs_read(this, arg) * inst->src[arg].stride *
-        type_sz(inst->src[arg].type)) > type_sz(entry->dst.type))
+   assert(entry->dst.file == GRF);
+   if (inst->src[arg].reg != entry->dst.reg)
       return false;
 
-   if (inst->src[arg].file != entry->dst.file ||
-       inst->src[arg].reg != entry->dst.reg ||
-       inst->src[arg].reg_offset != entry->dst.reg_offset ||
-       inst->src[arg].subreg_offset != entry->dst.subreg_offset) {
+   /* Bail if inst is reading a range that isn't contained in the range
+    * that entry is writing.
+    */
+   int reg_size = dispatch_width * sizeof(float);
+   if (inst->src[arg].reg_offset < entry->dst.reg_offset ||
+       (inst->src[arg].reg_offset * reg_size + inst->src[arg].subreg_offset +
+        inst->regs_read(this, arg) * inst->src[arg].stride * reg_size) >
+       (entry->dst.reg_offset + 1) * reg_size)
       return false;
-   }
 
    /* See resolve_ud_negate() and comment in brw_fs_emit.cpp. */
    if (inst->conditional_mod &&
@@ -361,11 +367,39 @@ fs_visitor::try_copy_propagate(fs_inst *inst, int arg, acp_entry *entry)
 
    inst->src[arg].file = entry->src.file;
    inst->src[arg].reg = entry->src.reg;
-   inst->src[arg].reg_offset = entry->src.reg_offset;
-   inst->src[arg].subreg_offset = entry->src.subreg_offset;
    inst->src[arg].stride *= entry->src.stride;
    inst->saturate = inst->saturate || entry->saturate;
 
+   switch (entry->src.file) {
+   case BAD_FILE:
+   case HW_REG:
+   case UNIFORM:
+      inst->src[arg].reg_offset = entry->src.reg_offset;
+      inst->src[arg].subreg_offset = entry->src.subreg_offset;
+      break;
+   case GRF:
+      {
+         /* In this case, we have to deal with mapping parts of vgrfs to
+          * other parts of vgrfs so we have to do some reg_offset magic.
+          */
+
+         /* Compute the offset of inst->src[arg] relative to inst->dst */
+         assert(entry->dst.subreg_offset == 0);
+         int rel_offset = inst->src[arg].reg_offset - entry->dst.reg_offset;
+         int rel_suboffset = inst->src[arg].subreg_offset;
+
+         /* Compute the final register offset (in bytes) */
+         int offset = entry->src.reg_offset * reg_size + entry->src.subreg_offset;
+         offset += rel_offset * reg_size + rel_suboffset;
+         inst->src[arg].reg_offset = offset / reg_size;
+         inst->src[arg].subreg_offset = offset % reg_size;
+      }
+      break;
+   default:
+      unreachable("Invalid register file");
+      break;
+   }
+
    if (!inst->src[arg].abs) {
       inst->src[arg].abs = entry->src.abs;
       inst->src[arg].negate ^= entry->src.negate;
@@ -375,9 +409,8 @@ fs_visitor::try_copy_propagate(fs_inst *inst, int arg, acp_entry *entry)
 }
 
 
-static bool
-try_constant_propagate(struct brw_context *brw, fs_inst *inst,
-                       acp_entry *entry)
+bool
+fs_visitor::try_constant_propagate(fs_inst *inst, acp_entry *entry)
 {
    bool progress = false;
 
@@ -385,12 +418,22 @@ try_constant_propagate(struct brw_context *brw, fs_inst *inst,
       return false;
 
    for (int i = inst->sources - 1; i >= 0; i--) {
-      if (inst->src[i].file != entry->dst.file ||
-          inst->src[i].reg != entry->dst.reg ||
-          inst->src[i].reg_offset != entry->dst.reg_offset ||
-          inst->src[i].subreg_offset != entry->dst.subreg_offset ||
-          inst->src[i].type != entry->dst.type ||
-          inst->src[i].stride > 1)
+      if (inst->src[i].file != GRF)
+         continue;
+
+      assert(entry->dst.file == GRF);
+      if (inst->src[i].reg != entry->dst.reg ||
+          inst->src[i].type != entry->dst.type)
+         continue;
+
+      /* Bail if inst is reading a range that isn't contained in the range
+       * that entry is writing.
+       */
+      int reg_size = dispatch_width * sizeof(float);
+      if (inst->src[i].reg_offset < entry->dst.reg_offset ||
+          (inst->src[i].reg_offset * reg_size + inst->src[i].subreg_offset +
+           inst->regs_read(this, i) * inst->src[i].stride * reg_size) >
+          (entry->dst.reg_offset + 1) * reg_size)
          continue;
 
       /* Don't bother with cases that should have been taken care of by the
@@ -546,7 +589,7 @@ fs_visitor::opt_copy_propagate_local(void *copy_prop_ctx, bblock_t *block,
             continue;
 
          foreach_in_list(acp_entry, entry, &acp[inst->src[i].reg % ACP_HASH_SIZE]) {
-            if (try_constant_propagate(brw, inst, entry))
+            if (try_constant_propagate(inst, entry))
                progress = true;
 
             if (try_copy_propagate(inst, i, entry))