[llvm-bugs] [Bug 43840] New: Loop peeling is errneously not performed - only considers inequality predicates

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=43840

            Bug ID: 43840
           Summary: Loop peeling is errneously not performed - only
                    considers inequality predicates
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Loop Optimizer
          Assignee: unassignedbugs at nondot.org
          Reporter: lebedev.ri at gmail.com
                CC: llvm-bugs at lists.llvm.org

Trivial example:

void init();
void sink();

void bad(int len) {
    for(int i = 0; i < len; i++) {
        if(i == 0) {
            init();
        }
        sink();
    }
}

It would make sense to peel the first iteration, so we no longer have
the always-false condition for the rest of the loop.
But the peeling does not happen!
https://godbolt.org/z/Y_wBgM

It does happen if *two* iterations should be peeled:
https://godbolt.org/z/RTf_QS

This appears to be an oversight: it only considers inequality comparisons,
it does not know how to deal with equality comparisons:
https://godbolt.org/z/1xmCKx

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