On Friday, August 08, 2014 02:42:27 PM Jason Ekstrand wrote:
> In particular, this caused problems where atomics operations were getting
> eliminated.
>
> Signed-off-by: Jason Ekstrand <jason.ekstr...@intel.com>
> ---
> src/mesa/drivers/dri/i965/brw_fs_cse.cpp | 3 ++-
> src/mesa/drivers/dri/i965/brw_vec4_cse.cpp | 3 ++-
> 2 files changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/src/mesa/drivers/dri/i965/brw_fs_cse.cpp
> b/src/mesa/drivers/dri/i965/brw_fs_cse.cpp
> index 63d87f9..8cfc6c6 100644
> --- a/src/mesa/drivers/dri/i965/brw_fs_cse.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_fs_cse.cpp
> @@ -177,7 +177,8 @@ fs_visitor::opt_cse_local(bblock_t *block)
> foreach_inst_in_block(fs_inst, inst, block) {
> /* Skip some cases. */
> if (is_expression(inst) && !inst->is_partial_write() &&
> - (inst->dst.file != HW_REG || inst->dst.is_null()))
> + (inst->dst.file != HW_REG || inst->dst.is_null()) &&
> + !inst->has_side_effects())
> {
> bool found = false;
>
> diff --git a/src/mesa/drivers/dri/i965/brw_vec4_cse.cpp
> b/src/mesa/drivers/dri/i965/brw_vec4_cse.cpp
> index 29d2e02..44651b4 100644
> --- a/src/mesa/drivers/dri/i965/brw_vec4_cse.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_vec4_cse.cpp
> @@ -135,7 +135,8 @@ vec4_visitor::opt_cse_local(bblock_t *block)
> foreach_inst_in_block (vec4_instruction, inst, block) {
> /* Skip some cases. */
> if (is_expression(inst) && !inst->predicate && inst->mlen == 0 &&
> - (inst->dst.file != HW_REG || inst->dst.is_null()))
> + (inst->dst.file != HW_REG || inst->dst.is_null()) &&
> + !inst->has_side_effects())
> {
> bool found = false;
>
>
I was confused at first because operations with side-effects should never have
been part of the whitelist of opcodes to CSE. But Matt generalized it in
1d97212007ccae, by changing is_expression()'s default case to "return
inst->is_send_from_grf()".
I think a better patch would be to change that to:
default:
return inst->is_send_from_grf() && !inst->has_side_effects();
It's also worth noting in your commit message that this is not actually fixing
a current bug, but rather preventing a regression once your patches that
convert atomics to send-from-GRFs land.
--Ken
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