[3.4 PATCH] Fix record_value_for_reg (PR rtl-optimization/15139)

[Mark Mitchell]

Jakub Jelinek wrote:
> Hi!
> 
> The following testcase on x86-64 eats needs I guess at least a dozen
> gigabytes of memory to compile.  The problem is that after unrolling, we
> have 30 really similar maxdf instructions updating one pseudo, there
> are 2 occurences of the pseudo in the insn
> (set (reg:DF 61) (if_then_else:DF (gt (reg:DF 61) (reg:DF 67))
> 		  		  (reg:DF 61) (reg:DF 67)))
> and as
>   /* If VALUE contains REG and we have a previous value for REG, substitute
>      the previous value.  */
>   if (value && insn && reg_overlap_mentioned_p (reg, value))
> is true, on each maxdf instruction the size of the recorded get_last_value*
> for (reg:DF 61) more than doubles.
> 
> The following patch adds a cap on the size of the last value if it is going
> to replace it into two or more places.  The 10000 rtxs was completely random
> number high enough that it IMHO shouldn't trigger too often, but still small
> enough that the testcase compiles instantly.
> Is this ok for gcc-3_4-branch if it bootstraps & testing succeeds?

This is OK -- if you use an appropriate --param instead of the magic 10000.

-- 
Mark Mitchell
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