[PATCH] fwprop: Avoid volatile defines to be propagated

[Jeff Law]

On 2/25/24 20:30, HAO CHEN GUI wrote:
> Hi,
>    This patch tries to fix a potential problem which is raised by the patch
> for PR111267. The volatile asm operand tries to be propagated to a single
> set insn with the patch for PR111267. It has potential risk as the behavior
> is wrong. Currently set_src_cost comparison can reject such propagation.
> But the propagation might be taken after replacing set_src_cost with insn
> cost. Actually I found the problem in testing my patch which replacing
> et_src_cost with insn cost for fwprop.
> 
>    Bootstrapped and tested on x86 and powerpc64-linux BE and LE with no
> regressions. Is it OK for the trunk?
> 
> Thanks
> Gui Haochen
> 
> ChangeLog
> fwprop: Avoid volatile defines to be propagated
> 
> The patch for PR111267 (commit id 86de9b66480b710202a2898cf513db105d8c432f)
> which introduces an exception for propagation on single set insn.  The
> propagation which might not be profitable (checked by profitable_p) is still
> allowed to be propagated to single set insn.  It has a potential problem
> that a volatile asm operand will try to be propagated to a single set insn.
> The volatile asm operand is originally banned in profitable_p.  This patch
> fixes the problem by skipping volatile set source in define set finding.
> 
> gcc/
> 	* fwprop.cc (forward_propagate_into): Return false for volatile set
> 	source.
> 
> gcc/testsuite/
> 	* gcc.target/powerpc/fwprop-1.c: New.
Why specifically are you worried here?  Propagation of a volatile 
shouldn't in and of itself cause a problem.  We're not changing the 
number of volatile accesses or anything like that -- we're just moving 
them around a bit.

Jeff