[llvm-bugs] [Bug 52547] New: [InstCombine] missed fold of icmp-of-casted-shift

via llvm-bugs llvm-bugs at lists.llvm.org
Thu Nov 18 07:13:38 PST 2021


            Bug ID: 52547
           Summary: [InstCombine] missed fold of icmp-of-casted-shift
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Scalar Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: spatel+llvm at rotateright.com
                CC: llvm-bugs at lists.llvm.org

Forking this off from bug 52543 - we may be able to generalize this further for
other constant values, but here's a missed sub-pattern based on that test:

define i1 @src(i32 %a) {
  %shl = shl i32 1, %a
  %t = trunc i32 %shl to i8
  %r = icmp eq i8 %t, 0
  ret i1 %r

define i1 @tgt(i32 %a) {
  %r = icmp ugt i32 %a, 7
  ret i1 %r


And the 'ne' sibling:

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