[Mesa-dev] [PATCH] i965/disasm: Properly decode branch_ctrl (gen8+)

[Ben Widawsky]

Add support for decoding the new branch control bit. I saw two things wrong with
the existing code.

1. It didn't bother trying to decode the bit.
-  While we do not *intentionally* emit this bit today, I think it's interesting
   to see if we somehow ended up with the bit set. It may also be useful in the
   future.

2. It seemed to be the wrong bit.
-  The docs are pretty poor wrt which bit this actually occupies. To me, it
   /looks/ like it should be bit 28. I am not sure where Ken got 30 from. I
   verified it should be 28 by looking at the simulator code.

I also added the most basic support for GOTO simply so we don't need to remember
to change the function in the future.

Cc: Kenneth Graunke <kenneth at whitecape.org>
Signed-off-by: Ben Widawsky <ben at bwidawsk.net>
---
 src/mesa/drivers/dri/i965/brw_defines.h |  1 +
 src/mesa/drivers/dri/i965/brw_disasm.c  | 29 ++++++++++++++++++++++++++---
 src/mesa/drivers/dri/i965/brw_inst.h    |  2 +-
 3 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_defines.h b/src/mesa/drivers/dri/i965/brw_defines.h
index 53cd75e..ed94bcc 100644
--- a/src/mesa/drivers/dri/i965/brw_defines.h
+++ b/src/mesa/drivers/dri/i965/brw_defines.h
@@ -820,6 +820,7 @@ enum opcode {
    BRW_OPCODE_MSAVE =	44,  /**< Pre-Gen6 */
    BRW_OPCODE_MRESTORE = 45, /**< Pre-Gen6 */
    BRW_OPCODE_PUSH =	46,  /**< Pre-Gen6 */
+   BRW_OPCODE_GOTO =	46,  /**< Gen8+    */
    BRW_OPCODE_POP =	47,  /**< Pre-Gen6 */
    BRW_OPCODE_WAIT =	48,
    BRW_OPCODE_SEND =	49,
diff --git a/src/mesa/drivers/dri/i965/brw_disasm.c b/src/mesa/drivers/dri/i965/brw_disasm.c
index 53ec767..013058e 100644
--- a/src/mesa/drivers/dri/i965/brw_disasm.c
+++ b/src/mesa/drivers/dri/i965/brw_disasm.c
@@ -131,6 +131,18 @@ has_uip(struct brw_context *brw, enum opcode opcode)
 }
 
 static bool
+has_branch_ctrl(struct brw_context *brw, enum opcode opcode)
+{
+   if (brw->gen < 8)
+      return false;
+
+   return opcode == BRW_OPCODE_IF ||
+          opcode == BRW_OPCODE_ELSE ||
+          opcode == BRW_OPCODE_GOTO ||
+          opcode == BRW_OPCODE_ENDIF;
+}
+
+static bool
 is_logic_instruction(unsigned opcode)
 {
    return opcode == BRW_OPCODE_AND ||
@@ -217,6 +229,11 @@ static const char *const accwr[2] = {
    [1] = "AccWrEnable"
 };
 
+static const char *const branch_ctrl[2] = {
+   [0] = "",
+   [1] = "BranchCtrl"
+};
+
 static const char *const wectrl[2] = {
    [0] = "",
    [1] = "WE_all"
@@ -1544,9 +1561,15 @@ brw_disassemble_inst(FILE *file, struct brw_context *brw, brw_inst *inst,
       err |= control(file, "compaction", cmpt_ctrl, is_compacted, &space);
       err |= control(file, "thread control", thread_ctrl,
                      brw_inst_thread_control(brw, inst), &space);
-      if (brw->gen >= 6)
-         err |= control(file, "acc write control", accwr,
-                        brw_inst_acc_wr_control(brw, inst), &space);
+      if (brw->gen >= 6) {
+         if (has_branch_ctrl(brw, opcode)) {
+            err |= control(file, "branch ctrl", branch_ctrl,
+                           brw_inst_branch_control(brw, inst), &space);
+         } else {
+            err |= control(file, "acc write control", accwr,
+                           brw_inst_acc_wr_control(brw, inst), &space);
+         }
+      }
       if (opcode == BRW_OPCODE_SEND || opcode == BRW_OPCODE_SENDC)
          err |= control(file, "end of thread", end_of_thread,
                         brw_inst_eot(brw, inst), &space);
diff --git a/src/mesa/drivers/dri/i965/brw_inst.h b/src/mesa/drivers/dri/i965/brw_inst.h
index c1ff10d..372aa2b 100644
--- a/src/mesa/drivers/dri/i965/brw_inst.h
+++ b/src/mesa/drivers/dri/i965/brw_inst.h
@@ -169,9 +169,9 @@ FF(flag_reg_nr,
    /* 8: */ 33, 33)
 F8(flag_subreg_nr,     /* 4+ */  89, 89, /* 8+ */ 32, 32)
 F(saturate,             31,  31)
-FC(branch_control,      30,  30, brw->gen >= 8)
 F(debug_control,        30,  30)
 F(cmpt_control,         29,  29)
+FC(branch_control,      28,  28, brw->gen >= 8)
 F(acc_wr_control,       28,  28)
 F(cond_modifier,        27,  24)
 FC(math_function,       27,  24, brw->gen >= 6)
-- 
2.1.3