[Mesa-dev] [PATCH 13/20] i965/fs: Do not move MOVs writing the flag outside of control flow

[Matt Turner]

The implementation of ballotARB() will start by zeroing the flags
register. So, a doing something like

        if (gl_SubGroupInvocationARB % 2u == 0u) {
                ... = ballotARB(true);
		[...]
        } else {
                ... = ballotARB(true);
		[...]
	}

(like fs-ballot-if-else.shader_test does) would generate identical MOVs
to the same destination (the flag register!), and we definitely do not
want to pull that out of the control flow.
---
 src/intel/compiler/brw_fs_sel_peephole.cpp | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/intel/compiler/brw_fs_sel_peephole.cpp b/src/intel/compiler/brw_fs_sel_peephole.cpp
index 8cd897f72e..fd02792beb 100644
--- a/src/intel/compiler/brw_fs_sel_peephole.cpp
+++ b/src/intel/compiler/brw_fs_sel_peephole.cpp
@@ -68,7 +68,8 @@ count_movs_from_if(fs_inst *then_mov[MAX_MOVS], fs_inst *else_mov[MAX_MOVS],
 {
    int then_movs = 0;
    foreach_inst_in_block(fs_inst, inst, then_block) {
-      if (then_movs == MAX_MOVS || inst->opcode != BRW_OPCODE_MOV)
+      if (then_movs == MAX_MOVS || inst->opcode != BRW_OPCODE_MOV ||
+          inst->flags_written())
          break;
 
       then_mov[then_movs] = inst;
@@ -77,7 +78,8 @@ count_movs_from_if(fs_inst *then_mov[MAX_MOVS], fs_inst *else_mov[MAX_MOVS],
 
    int else_movs = 0;
    foreach_inst_in_block(fs_inst, inst, else_block) {
-      if (else_movs == MAX_MOVS || inst->opcode != BRW_OPCODE_MOV)
+      if (else_movs == MAX_MOVS || inst->opcode != BRW_OPCODE_MOV ||
+          inst->flags_written())
          break;
 
       else_mov[else_movs] = inst;
-- 
2.13.0