[llvm] r219487 - APInt: Unfold return expressions so RVO can work.

[David Blaikie]

On Fri, Oct 10, 2014 at 3:18 AM, Benjamin Kramer <benny.kra at googlemail.com>
wrote:

> Author: d0k
> Date: Fri Oct 10 05:18:12 2014
> New Revision: 219487
>
> URL: http://llvm.org/viewvc/llvm-project?rev=219487&view=rev
> Log:
> APInt: Unfold return expressions so RVO can work.
>
> Saves a couple of expensive deep copies. NFC.
>

Perhaps somewhat annoying, but could we fix this more generically by
providing an rvalue overload of clearUnusedBits? (that returns by value,
moving out of the current object) I guess that'd still incur some moves,
rather than the completely free NRVO.


>
> Modified:
>     llvm/trunk/lib/Support/APInt.cpp
>
> Modified: llvm/trunk/lib/Support/APInt.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Support/APInt.cpp?rev=219487&r1=219486&r2=219487&view=diff
>
> ==============================================================================
> --- llvm/trunk/lib/Support/APInt.cpp (original)
> +++ llvm/trunk/lib/Support/APInt.cpp Fri Oct 10 05:18:12 2014
> @@ -454,8 +454,10 @@ APInt APInt::XorSlowCase(const APInt& RH
>    for (unsigned i = 0; i < numWords; ++i)
>      val[i] = pVal[i] ^ RHS.pVal[i];
>
> +  APInt Result(val, getBitWidth());
>    // 0^0==1 so clear the high bits in case they got set.
> -  return APInt(val, getBitWidth()).clearUnusedBits();
> +  Result.clearUnusedBits();
> +  return Result;
>  }
>
>  APInt APInt::operator*(const APInt& RHS) const {
> @@ -473,7 +475,8 @@ APInt APInt::operator+(const APInt& RHS)
>      return APInt(BitWidth, VAL + RHS.VAL);
>    APInt Result(BitWidth, 0);
>    add(Result.pVal, this->pVal, RHS.pVal, getNumWords());
> -  return Result.clearUnusedBits();
> +  Result.clearUnusedBits();
> +  return Result;
>  }
>
>  APInt APInt::operator-(const APInt& RHS) const {
> @@ -482,7 +485,8 @@ APInt APInt::operator-(const APInt& RHS)
>      return APInt(BitWidth, VAL - RHS.VAL);
>    APInt Result(BitWidth, 0);
>    sub(Result.pVal, this->pVal, RHS.pVal, getNumWords());
> -  return Result.clearUnusedBits();
> +  Result.clearUnusedBits();
> +  return Result;
>  }
>
>  bool APInt::EqualSlowCase(const APInt& RHS) const {
> @@ -1114,7 +1118,9 @@ APInt APInt::ashr(unsigned shiftAmt) con
>    uint64_t fillValue = (isNegative() ? -1ULL : 0);
>    for (unsigned i = breakWord+1; i < getNumWords(); ++i)
>      val[i] = fillValue;
> -  return APInt(val, BitWidth).clearUnusedBits();
> +  APInt Result(val, BitWidth);
> +  Result.clearUnusedBits();
> +  return Result;
>  }
>
>  /// Logical right-shift this APInt by shiftAmt.
> @@ -1151,7 +1157,9 @@ APInt APInt::lshr(unsigned shiftAmt) con
>    // If we are shifting less than a word, compute the shift with a simple
> carry
>    if (shiftAmt < APINT_BITS_PER_WORD) {
>      lshrNear(val, pVal, getNumWords(), shiftAmt);
> -    return APInt(val, BitWidth).clearUnusedBits();
> +    APInt Result(val, BitWidth);
> +    Result.clearUnusedBits();
> +    return Result;
>    }
>
>    // Compute some values needed by the remaining shift algorithms
> @@ -1164,7 +1172,9 @@ APInt APInt::lshr(unsigned shiftAmt) con
>        val[i] = pVal[i+offset];
>      for (unsigned i = getNumWords()-offset; i < getNumWords(); i++)
>        val[i] = 0;
> -    return APInt(val,BitWidth).clearUnusedBits();
> +    APInt Result(val, BitWidth);
> +    Result.clearUnusedBits();
> +    return Result;
>    }
>
>    // Shift the low order words
> @@ -1178,7 +1188,9 @@ APInt APInt::lshr(unsigned shiftAmt) con
>    // Remaining words are 0
>    for (unsigned i = breakWord+1; i < getNumWords(); ++i)
>      val[i] = 0;
> -  return APInt(val, BitWidth).clearUnusedBits();
> +  APInt Result(val, BitWidth);
> +  Result.clearUnusedBits();
> +  return Result;
>  }
>
>  /// Left-shift this APInt by shiftAmt.
> @@ -1211,7 +1223,9 @@ APInt APInt::shlSlowCase(unsigned shiftA
>        val[i] = pVal[i] << shiftAmt | carry;
>        carry = pVal[i] >> (APINT_BITS_PER_WORD - shiftAmt);
>      }
> -    return APInt(val, BitWidth).clearUnusedBits();
> +    APInt Result(val, BitWidth);
> +    Result.clearUnusedBits();
> +    return Result;
>    }
>
>    // Compute some values needed by the remaining shift algorithms
> @@ -1224,7 +1238,9 @@ APInt APInt::shlSlowCase(unsigned shiftA
>        val[i] = 0;
>      for (unsigned i = offset; i < getNumWords(); i++)
>        val[i] = pVal[i-offset];
> -    return APInt(val,BitWidth).clearUnusedBits();
> +    APInt Result(val, BitWidth);
> +    Result.clearUnusedBits();
> +    return Result;
>    }
>
>    // Copy whole words from this to Result.
> @@ -1235,7 +1251,9 @@ APInt APInt::shlSlowCase(unsigned shiftA
>    val[offset] = pVal[0] << wordShift;
>    for (i = 0; i < offset; ++i)
>      val[i] = 0;
> -  return APInt(val, BitWidth).clearUnusedBits();
> +  APInt Result(val, BitWidth);
> +  Result.clearUnusedBits();
> +  return Result;
>  }
>
>  APInt APInt::rotl(const APInt &rotateAmt) const {
>
>
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