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From: "aldyh at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/103409] [12 Regression] 18% SPEC2017 WRF
 compile-time regression with -O2 -flto since
 r12-5228-gb7a23949b0dcc4205fcc2be6b84b91441faa384d
Date: Mon, 29 Nov 2021 14:36:36 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103409

--- Comment #10 from Aldy Hernandez <aldyh at gcc dot gnu.org> ---
Created attachment 51896
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D51896&action=3Dedit
untested patch

The threading slowdown here is due to the ssa_global_cache temporary.  It
doesn't look like ssa_global_cache was meant to be lightweight temporary ca=
che
;-).

We can avoid the temporary altogether by using the bitmap already used to
determine if a cache entry is available.  With this (untested) patch the
ltrans42 unit is back to:

 tree VRP                           :  13.70 (  3%)   0.04 (  2%)  13.71 ( =
 3%)
   45M (  4%)
 backwards jump threading           :  13.22 (  3%)   0.01 (  0%)  13.26 ( =
 3%)
 3609k (  0%)=