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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/103821] New: [12 Regression] huge compile
 time (jump threading) at -O3 for simple code
Date: Thu, 23 Dec 2021 20:14:12 +0000
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X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 12.0
X-Bugzilla-Keywords: compile-time-hog
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103821

            Bug ID: 103821
           Summary: [12 Regression] huge compile time (jump threading) at
                    -O3 for simple code
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Keywords: compile-time-hog
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---

Take:
    #include <inttypes.h>
    uint16_t int_sqrt32(uint32_t x)
    {
        uint16_t res=3D0;
        uint16_t add=3D 0x8000;=20=20=20
        do {
            uint16_t temp=3Dres | add;
            uint32_t g2=3Dtemp*temp;=20=20=20=20=20=20
            if (x>=3Dg2)
                res=3Dtemp;=20=20=20=20=20=20=20=20=20=20=20
            add>>=3D1;
        } while(add);
        return res;
    }
----- CUT -----
Compile this at -O3 and GCC takes a long time:
 backwards jump threading           :  20.12 ( 81%)   0.01 ( 50%)  20.12 ( =
78%)
   26M ( 79%)=