[llvm-bugs] [Bug 37636] New: InstCombine produces worse code when provided with range information

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=37636

            Bug ID: 37636
           Summary: InstCombine produces worse code when provided with
                    range information
           Product: new-bugs
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: max.kazantsev at azul.com
                CC: llvm-bugs at lists.llvm.org

Instcombine can sometimes produce a worse code when dealing with values
annotated by ranges than if there was no range. Apparently it tries to replace
sdiv with bit magic and it breaks some other pattern recognition.

Tests:

define i1 @good(i32* %A) {
  %A.val = load i32, i32* %A, align 8
  %B = sdiv i32 %A.val, 2
  %C = icmp sge i32 0, %B
  ret i1 %C
}

define i1 @bad(i32* %A) {
  %A.val = load i32, i32* %A, align 8, !range !0
  %B = sdiv i32 %A.val, 2
  %C = icmp sge i32 0, %B
  ret i1 %C
}

!0 = !{i32 0, i32 2147483647}

Run opt -instcombine -S

The result is:

define i1 @good(i32* %A) {
  %A.val = load i32, i32* %A, align 8
  %C = icmp slt i32 %A.val, 2
  ret i1 %C
}

define i1 @bad(i32* %A) {
  %A.val = load i32, i32* %A, align 8, !range !0
  %B.mask = and i32 %A.val, 2147483646
  %C = icmp eq i32 %B.mask, 0
  ret i1 %C
}

!0 = !{i32 0, i32 2147483647}

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