[Mesa-dev] [PATCH 2/2] i965/fs: fix copy propagation of partially invalidated entries

[Iago Toral Quiroga]

We were not invalidating entries with a src that reads more than 1 register
when we find writes that overwrite any register read by entry->src after
the first. This leads to incorrect copy propagation because we re-use
entries from the ACP that have been partially invalidated.
---
 .../drivers/dri/i965/brw_fs_copy_propagation.cpp   | 22 +++++++++++++++++-----
 1 file changed, 17 insertions(+), 5 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 3e89a0d..89ba8c5 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp
@@ -44,6 +44,7 @@ struct acp_entry : public exec_node {
    fs_reg dst;
    fs_reg src;
    uint8_t regs_written;
+   uint8_t regs_read;
    enum opcode opcode;
    bool saturate;
 };
@@ -775,8 +776,17 @@ fs_visitor::opt_copy_propagate_local(void *copy_prop_ctx, bblock_t *block,
           */
          for (int i = 0; i < ACP_HASH_SIZE; i++) {
             foreach_in_list_safe(acp_entry, entry, &acp[i]) {
-               if (inst->overwrites_reg(entry->src))
-                  entry->remove();
+               /* Make sure we kill the entry if this instructions overwrites
+                * _any_ of the registers that it reads
+                */
+               fs_reg tmp = entry->src;
+               for (int n = 0; n < entry->regs_read; n++) {
+                  if (inst->overwrites_reg(tmp)) {
+                     entry->remove();
+                     break;
+                  }
+                  tmp.reg_offset++;
+               }
             }
 	 }
       }
@@ -785,10 +795,11 @@ fs_visitor::opt_copy_propagate_local(void *copy_prop_ctx, bblock_t *block,
        * operand of another instruction, add it to the ACP.
        */
       if (can_propagate_from(inst)) {
-	 acp_entry *entry = ralloc(copy_prop_ctx, acp_entry);
-	 entry->dst = inst->dst;
-	 entry->src = inst->src[0];
+         acp_entry *entry = ralloc(copy_prop_ctx, acp_entry);
+         entry->dst = inst->dst;
+         entry->src = inst->src[0];
          entry->regs_written = inst->regs_written;
+         entry->regs_read = inst->regs_read(0);
          entry->opcode = inst->opcode;
          entry->saturate = inst->saturate;
          acp[entry->dst.nr % ACP_HASH_SIZE].push_tail(entry);
@@ -804,6 +815,7 @@ fs_visitor::opt_copy_propagate_local(void *copy_prop_ctx, bblock_t *block,
                entry->dst.reg_offset = offset;
                entry->src = inst->src[i];
                entry->regs_written = regs_written;
+               entry->regs_read = inst->regs_read(i);
                entry->opcode = inst->opcode;
                if (!entry->dst.equals(inst->src[i])) {
                   acp[entry->dst.nr % ACP_HASH_SIZE].push_tail(entry);
-- 
2.1.4