[Mesa-dev] [PATCH 2/2] i965: Don't overwrite the math SFID with conditional mod.

[Matt Turner]

Ben was asking about the undocumented restriction that the math
instruction cannot use the dependency control hints. I went to reconfirm
and disabled the is_math() check in opt_set_dependency_control() and saw
that the disassembled math instructions with dependency hints had a
bogus SFID. We were mistakenly overwriting it by setting an empty
conditional mod.

Unfortunately, this wasn't the cause of the aforementioned problem (I
reproduced it). This bug is benign, since we don't set dependeny hints
on math instructions -- but maybe some day.
---
Interestingly the BSpec now says about the math instruction:

	Restriction : DepCtrl must not be used.

but only lists BDW and newer generations, so it seems like if pre-BDW is
known broken and BDW and newer can't set DepCtrl, it might be a while.

 src/mesa/drivers/dri/i965/brw_fs_generator.cpp   | 3 ++-
 src/mesa/drivers/dri/i965/brw_vec4_generator.cpp | 3 ++-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_fs_generator.cpp b/src/mesa/drivers/dri/i965/brw_fs_generator.cpp
index 4af9cbe..06b0f34 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_generator.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_generator.cpp
@@ -2010,7 +2010,8 @@ fs_generator::generate_code(const cfg_t *cfg, int dispatch_width)
 
          brw_inst *last = &p->store[last_insn_offset / 16];
 
-         brw_inst_set_cond_modifier(brw, last, inst->conditional_mod);
+         if (inst->conditional_mod)
+            brw_inst_set_cond_modifier(brw, last, inst->conditional_mod);
          brw_inst_set_no_dd_clear(brw, last, inst->no_dd_clear);
          brw_inst_set_no_dd_check(brw, last, inst->no_dd_check);
       }
diff --git a/src/mesa/drivers/dri/i965/brw_vec4_generator.cpp b/src/mesa/drivers/dri/i965/brw_vec4_generator.cpp
index d027fda..6a70a2f 100644
--- a/src/mesa/drivers/dri/i965/brw_vec4_generator.cpp
+++ b/src/mesa/drivers/dri/i965/brw_vec4_generator.cpp
@@ -1509,7 +1509,8 @@ vec4_generator::generate_code(const cfg_t *cfg)
 
          brw_inst *last = &p->store[pre_emit_nr_insn];
 
-         brw_inst_set_cond_modifier(brw, last, inst->conditional_mod);
+         if (inst->conditional_mod)
+            brw_inst_set_cond_modifier(brw, last, inst->conditional_mod);
          brw_inst_set_no_dd_clear(brw, last, inst->no_dd_clear);
          brw_inst_set_no_dd_check(brw, last, inst->no_dd_check);
       }
-- 
2.0.4