i965/fs: Add support for specifying register horizontal strides.

v2: Some improvements for copy propagation with non-contiguous
    register strides and mismatching types.
v3: Add example of the situation that the copy propagation changes are
    intended to avoid.  Clarify that 'fs_reg::apply_stride()' is expected
    to work with zero strides too.

Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Paul Berry <stereotype441@gmail.com>

1 files changed, 33 insertions, 3 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 5cf019c..cdb7b80 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp
@@ -279,7 +279,9 @@ fs_visitor::try_copy_propagate(fs_inst *inst, int arg, acp_entry *entry)
    if (entry->src.file == IMM)
       return false;
 
-   if (inst->regs_read(this, arg) > 1)
+   /* 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))
       return false;
 
    if (inst->src[arg].file != entry->dst.file ||
@@ -298,7 +300,32 @@ fs_visitor::try_copy_propagate(fs_inst *inst, int arg, acp_entry *entry)
    bool has_source_modifiers = entry->src.abs || entry->src.negate;
 
    if ((has_source_modifiers || entry->src.file == UNIFORM ||
-        entry->src.smear != -1) && !can_do_source_mods(inst))
+        entry->src.smear != -1 || !entry->src.is_contiguous()) &&
+       !can_do_source_mods(inst))
+      return false;
+
+   /* Bail if the result of composing both strides would exceed the
+    * hardware limit.
+    */
+   if (entry->src.stride * inst->src[arg].stride > 4)
+      return false;
+
+   /* Bail if the result of composing both strides cannot be expressed
+    * as another stride. This avoids, for example, trying to transform
+    * this:
+    *
+    *     MOV (8) rX<1>UD rY<0;1,0>UD
+    *     FOO (8) ...     rX<8;8,1>UW
+    *
+    * into this:
+    *
+    *     FOO (8) ...     rY<0;1,0>UW
+    *
+    * Which would have different semantics.
+    */
+   if (entry->src.stride != 1 &&
+       (inst->src[arg].stride *
+        type_sz(inst->src[arg].type)) % type_sz(entry->src.type) != 0)
       return false;
 
    if (has_source_modifiers && entry->dst.type != inst->src[arg].type)
@@ -310,6 +337,7 @@ fs_visitor::try_copy_propagate(fs_inst *inst, int arg, acp_entry *entry)
    if (entry->src.smear != -1)
       inst->src[arg].smear = entry->src.smear;
    inst->src[arg].subreg_offset = entry->src.subreg_offset;
+   inst->src[arg].stride *= entry->src.stride;
 
    if (!inst->src[arg].abs) {
       inst->src[arg].abs = entry->src.abs;
@@ -332,7 +360,9 @@ fs_visitor::try_constant_propagate(fs_inst *inst, acp_entry *entry)
       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].subreg_offset != entry->dst.subreg_offset ||
+          inst->src[i].type != entry->dst.type ||
+          inst->src[i].stride > 1)
          continue;
 
       /* Don't bother with cases that should have been taken care of by the