[llvm-bugs] [Bug 28668] New: [InstCombine] missing folds for bit manipulation intrinsics

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=28668

            Bug ID: 28668
           Summary: [InstCombine] missing folds for bit manipulation
                    intrinsics
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Scalar Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: spatel+llvm at rotateright.com
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

define i1 @ctlz_cmp(i32 %a) {
  %x = tail call i32 @llvm.ctlz.i32(i32 %a, i1 false) #0
  %cmp = icmp eq i32 %x, 0  ; no zeros? --> all ones
  ret i1 %cmp
}

define i1 @cttz_cmp(i32 %a) {
  %x = tail call i32 @llvm.cttz.i32(i32 %a, i1 false) #0
  %cmp = icmp eq i32 %x, 0  ; no zeros? --> all ones
  ret i1 %cmp
}

define i1 @ctpop_cmp(i32 %a) {
  %x = tail call i32 @llvm.ctpop.i32(i32 %a) #0
  %cmp = icmp eq i32 %x, 32 ; all ones? --> no zeros
  ret i1 %cmp
}

-----------------------------------------------------------------------------

$ ./opt -instcombine more_bitz.ll -S

(doesn't change anything)

Note that these all work:

define i1 @ctlz_cmp(i32 %a) {
  %x = tail call i32 @llvm.ctlz.i32(i32 %a, i1 false) nounwind readnone
  %cmp = icmp eq i32 %x, 32  ; all zeros? --> no ones
  ret i1 %cmp
}

define i1 @cttz_cmp(i32 %a) {
  %x = tail call i32 @llvm.cttz.i32(i32 %a, i1 false) nounwind readnone
  %cmp = icmp eq i32 %x, 32  ; all zeros? --> no ones
  ret i1 %cmp
}

define i1 @ctpop_cmp(i32 %a) {
  %x = tail call i32 @llvm.ctpop.i32(i32 %a) nounwind readnone
  %cmp = icmp eq i32 %x, 0   ; no ones? --> all zeros
  ret i1 %cmp
}

$ ./opt -instcombine more_bitz.ll -S
...
define i1 @ctlz_cmp(i32 %a) {
  %cmp = icmp eq i32 %a, 0
  ret i1 %cmp
}

define i1 @cttz_cmp(i32 %a) {
  %cmp = icmp eq i32 %a, 0
  ret i1 %cmp
}

define i1 @ctpop_cmp(i32 %a) {
  %cmp = icmp eq i32 %a, 0
  ret i1 %cmp
}

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