Ian Romanick <[email protected]> writes: > From: Ian Romanick <[email protected]> > > This provides a trivial simplification now, and it makes some future > changes more straight forward. > > Signed-off-by: Ian Romanick <[email protected]> > --- > src/mesa/drivers/dri/i965/brw_dead_control_flow.cpp | 12 +++++++----- > 1 file changed, 7 insertions(+), 5 deletions(-) > > diff --git a/src/mesa/drivers/dri/i965/brw_dead_control_flow.cpp > b/src/mesa/drivers/dri/i965/brw_dead_control_flow.cpp > index 716e2bc..7aa72b1 100644 > --- a/src/mesa/drivers/dri/i965/brw_dead_control_flow.cpp > +++ b/src/mesa/drivers/dri/i965/brw_dead_control_flow.cpp > @@ -41,7 +41,9 @@ dead_control_flow_eliminate(backend_shader *s) > bool progress = false; > > foreach_block_safe (block, s->cfg) { > + bblock_t *prev_block = block->prev(); > backend_instruction *const inst = block->start(); > + backend_instruction *prev_inst = prev_block->end(); > Just noticed that this change is bogus when 'block' is the first block of the program: block->prev() will return an incorrectly casted pointer to the head sentinel and prev_block->end() will then read invalid memory.
Any suggestions?
> /* ENDIF instructions, by definition, can only be found at the start of
> * basic blocks.
> @@ -52,20 +54,20 @@ dead_control_flow_eliminate(backend_shader *s)
> backend_instruction *endif_inst = inst;
>
> backend_instruction *if_inst = NULL, *else_inst = NULL;
> - backend_instruction *prev_inst = endif_block->prev()->end();
> if (prev_inst->opcode == BRW_OPCODE_ELSE) {
> else_inst = prev_inst;
> else_block = endif_block->prev();
> found = true;
>
> - if (else_block->start_ip == else_block->end_ip)
> - prev_inst = else_block->prev()->end();
> + if (else_block->start_ip == else_block->end_ip) {
> + prev_block = prev_block->prev();
> + prev_inst = prev_block->end();
> + }
> }
>
> if (prev_inst->opcode == BRW_OPCODE_IF) {
> if_inst = prev_inst;
> - if_block = else_block != NULL ? else_block->prev()
> - : endif_block->prev();
> + if_block = prev_block;
> found = true;
> } else {
> /* Don't remove the ENDIF if we didn't find a dead IF. */
> --
> 2.5.0
>
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