On 10/25/23 10:25, Vineet Gupta wrote:
Hey Robin,
On 10/25/23 00:12, Robin Dapp wrote:
Hi Vineet,
I was thinking of two things while skimming the code:
- Couldn't we do this in the expanders directly? Or is the
subreg-promoted info gone until we reach that?
Following is the call stack involved:
expand_gimple_cond
do_compare_and_jump
emit_cmp_and_jump_insns
gen_cbranchqi4
riscv_expand_conditional_branch
riscv_emit_int_compare
riscv_extend_comparands
Last function is what introduces the extraneous sign extends, w/o taking
subreg-promoted into consideration and what my patch attempts to address.
- Should some common-code part be more suited to handle that?
We already elide redundant sign-zero extensions for other
reasons. Maybe we could add subreg promoted handling there?
Not in the context of this specific issue.
Robin's point (IIUC) is that if we put this logic into a zero/sign
extend expander, then it'll get used for *any* attempt to zero/sign
extend that goes through the target expander.
It doesn't work for your case because we use gen_rtx_{ZERO,SIGN}_EXTEND
directly. But if those were adjusted to use the expander, then Robin's
idea would be applicable to this case too.
Jeff
