[IR] Implement...

[IR] Implement Constant::isNegativeZeroValue/isZeroValue/isAllOnesValue/isOneValue/isMinSignedValue for ConstantDataVector without going through getElementAsConstant

Summary:
Currently these methods call ConstantDataVector::getSplatValue which uses getElementsAsConstant to create a Constant object representing the element value. This method incurs a map lookup to see if we already have created such a Constant before and if not allocates a new Constant object.

This patch changes these methods to use getElementAsAPFloat and getElementAsInteger so we can just examine the data values directly.

Reviewers: spatel, pcc, dexonsmith, bogner, craig.topper

Reviewed By: craig.topper

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D35040

llvm-svn: 308112