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From: "xxs_chy at outlook dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/112982] New: Missing optimization: fold
 max(b, a + 1) to b when a < b
Date: Tue, 12 Dec 2023 10:24:34 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 14.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D112982

            Bug ID: 112982
           Summary: Missing optimization: fold max(b, a + 1) to b when a <
                    b
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: xxs_chy at outlook dot com
  Target Milestone: ---

Godbolt example: https://godbolt.org/z/nn8hT16Ka

long src(long a, long b) {
    if(a < b){
        return max(b, a + 1);
    }else{
        return 0;
    }
}

can be folded to:

long tgt(long a, long b) {
    if(a < b){
        return b;
    }else{
        return 0;
    }
}

Similarly, such pattern can be generalized to `a > b`, `min(b, a + 1)`.
Both GCC and LLVM missed such optimization opportunity.=