[Mesa-dev] [PATCH v2 09/30] i965/fs: fix copy/constant propagation regioning checks

[Samuel Iglesias Gonsálvez]

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

We were not accounting for subreg_offset in the check for the start
of the region.

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.

v2 (Sam):
- Rename function and add comment (Jason, Curro).
- Assert that register files and number are the same (Jason).
- Fix code to take into account the assumption that src.subreg_offset
is strictly less than the reg_offset unit (Curro).
- Don't pass the registers by value to the function, use
'const fs_reg &' instead (Curro).
- Remove obsolete comment in the commit log (Curro).

Reviewed-by: Kenneth Graunke <kenneth at whitecape.org>
Reviewed-by: Francisco Jerez <currojerez at riseup.net>
---
 .../drivers/dri/i965/brw_fs_copy_propagation.cpp   | 28 +++++++++++++++-------
 1 file changed, 20 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 4791894..084d315 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp
@@ -330,6 +330,22 @@ can_take_stride(fs_inst *inst, unsigned arg, unsigned stride,
    return true;
 }
 
+/**
+ * Check that the register region read by src [src.reg_offset,
+ * src.reg_offset + regs_read] is contained inside the register
+ * region written by dst [dst.reg_offset, dst.reg_offset + regs_written]
+ * Both src and dst must have the same register number and file.
+ */
+static inline bool
+regions_contained_in(const fs_reg &src, unsigned regs_read,
+                     const fs_reg &dst, unsigned regs_written)
+{
+   assert(src.file == dst.file && src.nr == dst.nr);
+   return (src.reg_offset * REG_SIZE + src.subreg_offset >=
+           dst.reg_offset * REG_SIZE + dst.subreg_offset) &&
+      src.reg_offset + regs_read <= dst.reg_offset + regs_written;
+}
+
 bool
 fs_visitor::try_copy_propagate(fs_inst *inst, int arg, acp_entry *entry)
 {
@@ -352,10 +368,8 @@ 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 (!regions_contained_in(inst->src[arg], inst->regs_read(arg),
+                             entry->dst, entry->regs_written))
       return false;
 
    /* we can't generally copy-propagate UD negations because we
@@ -520,10 +534,8 @@ 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 (!regions_contained_in(inst->src[i], inst->regs_read(i),
+                                entry->dst, entry->regs_written))
          continue;
 
       fs_reg val = entry->src;
-- 
2.5.0