[Mesa-dev] [PATCH 06/23] i965/fs: fix copy/constant propagation regioning checks

[Samuel Iglesias Gonsálvez]

From: Iago Toral Quiroga <itoral at igalia.com>

We were not accounting for reg_suboffset in the check for the start
of the region. This meant that would allow copy-propagation even if
the dst wrote to sub_regoffset 4 and our source read from
sub_regoffset 0, which is not correct. This was observed in fp64 code,
since there we use reg_suboffset to select the high 32-bit of a double.

Also, fs_reg::regs_read() already takes the stride into account, so we
should not multiply its result by the stride again. This was making
copy-propagation fail to copy-propagate cases that would otherwise be
safe to copy-propagate. Again, this was observed in fp64 code, since
there we use stride > 1 often.

Incidentally, these fixes open up more possibilities for copy propagation
which uncovered new bugs in copy-propagation. The folowing patches address
each of these new issues.
---
 .../drivers/dri/i965/brw_fs_copy_propagation.cpp    | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 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 5fae10f..23df877 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp
@@ -329,6 +329,15 @@ can_take_stride(fs_inst *inst, unsigned arg, unsigned stride,
    return true;
 }
 
+static inline bool
+region_match(fs_reg src, unsigned regs_read,
+             fs_reg dst, unsigned regs_written)
+{
+   return src.reg_offset >= dst.reg_offset &&
+          (src.reg_offset + regs_read) <= (dst.reg_offset + regs_written) &&
+          src.subreg_offset >= dst.subreg_offset;
+}
+
 bool
 fs_visitor::try_copy_propagate(fs_inst *inst, int arg, acp_entry *entry)
 {
@@ -351,10 +360,8 @@ fs_visitor::try_copy_propagate(fs_inst *inst, int arg, acp_entry *entry)
    /* Bail if inst is reading a range that isn't contained in the range
     * that entry is writing.
     */
-   if (inst->src[arg].reg_offset < entry->dst.reg_offset ||
-       (inst->src[arg].reg_offset * 32 + inst->src[arg].subreg_offset +
-        inst->regs_read(arg) * inst->src[arg].stride * 32) >
-       (entry->dst.reg_offset + entry->regs_written) * 32)
+   if (!region_match(inst->src[arg], inst->regs_read(arg),
+                     entry->dst, entry->regs_written))
       return false;
 
    /* we can't generally copy-propagate UD negations because we
@@ -554,10 +561,8 @@ fs_visitor::try_constant_propagate(fs_inst *inst, acp_entry *entry)
       /* Bail if inst is reading a range that isn't contained in the range
        * that entry is writing.
        */
-      if (inst->src[i].reg_offset < entry->dst.reg_offset ||
-          (inst->src[i].reg_offset * 32 + inst->src[i].subreg_offset +
-           inst->regs_read(i) * inst->src[i].stride * 32) >
-          (entry->dst.reg_offset + entry->regs_written) * 32)
+      if (!region_match(inst->src[i], inst->regs_read(i),
+                        entry->dst, entry->regs_written))
          continue;
 
       fs_reg val = entry->src;
-- 
2.5.0