[llvm-bugs] [Bug 26638] New: RLEV does not optimize loop

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=26638

            Bug ID: 26638
           Summary: RLEV does not optimize loop
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Loop Optimizer
          Assignee: unassignedbugs at nondot.org
          Reporter: sanjoy at playingwithpointers.com
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

I'd expect -indvars to RLEV away `%count.0.lcssa` in the loop below:

target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-apple-macosx10.11.0"

define i32 @count_odds(i32 %lim) {
entry:
  %cmp8 = icmp sgt i32 %lim, 0
  br i1 %cmp8, label %for.body, label %for.cond.cleanup

for.cond.cleanup:                                 ; preds = %for.body, %entry
  %count.0.lcssa = phi i32 [ 0, %entry ], [ %count.0.inc, %for.body ]
  ret i32 %count.0.lcssa

for.body:                                         ; preds = %entry, %for.body
  %i.010 = phi i32 [ %inc2, %for.body ], [ 0, %entry ]
  %count.09 = phi i32 [ %count.0.inc, %for.body ], [ 0, %entry ]
  %and = and i32 %i.010, 1
  %count.0.inc = add i32 %and, %count.09
  %inc2 = add i32 %i.010, 1
  %exitcond = icmp eq i32 %inc2, %lim
  br i1 %exitcond, label %for.cond.cleanup, label %for.body
}

In C, this roughly corresponds to

int count_odds(int lim) {
  int count = 0;
  for (int i = 0; i < lim; i++)
    if ((i & 1) == 1)
      count++;
  return count;
}

(except that I've removed the nsw and nuws)

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