[llvm] b38d897 - [ConstantRange] binaryXor(): special-case binary complement case - the result is precise

[Nikita Popov via llvm-commits]

On Tue, Sep 22, 2020 at 8:38 PM Roman Lebedev via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

>
> Author: Roman Lebedev
> Date: 2020-09-22T21:37:29+03:00
> New Revision: b38d897e802664034c7e6e4654328256ed370a61
>
> URL:
> https://github.com/llvm/llvm-project/commit/b38d897e802664034c7e6e4654328256ed370a61
> DIFF:
> https://github.com/llvm/llvm-project/commit/b38d897e802664034c7e6e4654328256ed370a61.diff
>
> LOG: [ConstantRange] binaryXor(): special-case binary complement case -
> the result is precise
>
> Use the fact that `~X` is equivalent to `-1 - X`, which gives us
> fully-precise answer, and we only need to special-handle the wrapped case.
>
> This fires ~16k times for vanilla llvm test-suite + RawSpeed.
>
> Added:
>
>
> Modified:
>     llvm/include/llvm/IR/ConstantRange.h
>     llvm/lib/IR/ConstantRange.cpp
>     llvm/unittests/IR/ConstantRangeTest.cpp
>
> Removed:
>
>
>
>
> ################################################################################
> diff  --git a/llvm/include/llvm/IR/ConstantRange.h
> b/llvm/include/llvm/IR/ConstantRange.h
> index 318532b24e83..494a14a10cdb 100644
> --- a/llvm/include/llvm/IR/ConstantRange.h
> +++ b/llvm/include/llvm/IR/ConstantRange.h
> @@ -409,6 +409,11 @@ class LLVM_NODISCARD ConstantRange {
>    /// value in \p Other.
>    ConstantRange srem(const ConstantRange &Other) const;
>
> +  /// Return a new range representing the possible values resulting from
> +  /// a binary-xor of a value in this range by an all-one value,
> +  /// aka bitwise complement operation.
> +  ConstantRange binaryNot() const;
> +
>    /// Return a new range representing the possible values resulting
>    /// from a binary-and of a value in this range by a value in \p Other.
>    ConstantRange binaryAnd(const ConstantRange &Other) const;
>
> diff  --git a/llvm/lib/IR/ConstantRange.cpp b/llvm/lib/IR/ConstantRange.cpp
> index 396c39b5b3a8..7b8dd66b993c 100644
> --- a/llvm/lib/IR/ConstantRange.cpp
> +++ b/llvm/lib/IR/ConstantRange.cpp
> @@ -1240,6 +1240,16 @@ ConstantRange ConstantRange::srem(const
> ConstantRange &RHS) const {
>    return ConstantRange(std::move(Lower), std::move(Upper));
>  }
>
> +ConstantRange ConstantRange::binaryNot() const {
> +  if (isEmptySet())
> +    return getEmpty();
> +
> +  if (isWrappedSet())
> +    return getFull();
>

Probably don't need those checks, as you're forwarding to the sub()
implementation anyway?

Nikita


> +
> +  return ConstantRange(APInt::getAllOnesValue(getBitWidth())).sub(*this);
> +}
> +
>  ConstantRange
>  ConstantRange::binaryAnd(const ConstantRange &Other) const {
>    if (isEmptySet() || Other.isEmptySet())
> @@ -1278,6 +1288,12 @@ ConstantRange ConstantRange::binaryXor(const
> ConstantRange &Other) const {
>    if (isSingleElement() && Other.isSingleElement())
>      return {*getSingleElement() ^ *Other.getSingleElement()};
>
> +  // Special-case binary complement, since we can give a precise answer.
> +  if (Other.isSingleElement() &&
> Other.getSingleElement()->isAllOnesValue())
> +    return binaryNot();
> +  if (isSingleElement() && getSingleElement()->isAllOnesValue())
> +    return Other.binaryNot();
> +
>    // TODO: replace this with something less conservative
>    return getFull();
>  }
>
> diff  --git a/llvm/unittests/IR/ConstantRangeTest.cpp
> b/llvm/unittests/IR/ConstantRangeTest.cpp
> index 8bcc6efdc265..474a94af3932 100644
> --- a/llvm/unittests/IR/ConstantRangeTest.cpp
> +++ b/llvm/unittests/IR/ConstantRangeTest.cpp
> @@ -2349,4 +2349,22 @@ TEST_F(ConstantRangeTest, binaryXor) {
>    EXPECT_TRUE(R0_99.binaryXor(R16_35).isFullSet());
>  }
>
> +TEST_F(ConstantRangeTest, binaryNot) {
> +  TestUnsignedUnaryOpExhaustive(
> +      [](const ConstantRange &CR) { return CR.binaryNot(); },
> +      [](const APInt &N) { return ~N; });
> +  TestUnsignedUnaryOpExhaustive(
> +      [](const ConstantRange &CR) {
> +        return CR.binaryXor(
> +            ConstantRange(APInt::getAllOnesValue(CR.getBitWidth())));
> +      },
> +      [](const APInt &N) { return ~N; });
> +  TestUnsignedUnaryOpExhaustive(
> +      [](const ConstantRange &CR) {
> +        return ConstantRange(APInt::getAllOnesValue(CR.getBitWidth()))
> +            .binaryXor(CR);
> +      },
> +      [](const APInt &N) { return ~N; });
> +}
> +
>  }  // anonymous namespace
>
>
>
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