This consolidates node definitions into one place and enables automatic
node verification.

Part of #119709.

…on returning { i8, i128 }

Fixes https://github.com/llvm/llvm-project/issues/96432.

This helper function shortens examples like
`cast<ConstantSDNode>(Node->getOperand(1))->getZExtValue();` to
`Node->getConstantOperandVal(1);`.

Implemented with:
`git grep -l
"cast<ConstantSDNode>\(.*->getOperand\(.*\)\)->getZExtValue\(\)" | xargs
sed -E -i

's/cast<ConstantSDNode>\((.*)->getOperand\((.*)\)\)->getZExtValue\(\)/\1->getConstantOperandVal(\2)/`
and `git grep -l
"cast<ConstantSDNode>\(.*\.getOperand\(.*\)\)->getZExtValue\(\)" | xargs
sed -E -i

's/cast<ConstantSDNode>\((.*)\.getOperand\((.*)\)\)->getZExtValue\(\)/\1.getConstantOperandVal(\2)/'`.
With a couple of simple manual fixes needed. Result then processed by
`git clang-format`.

Optimize "Rx * imm" for specific immediates to
([IXH32|IXW32|IXD32] (LSLI Rx, shift), Rx).

Reviewed By: zixuan-wu

Differential Revision: https://reviews.llvm.org/D154768

Reviewed By: zixuan-wu

Differential Revision: https://reviews.llvm.org/D156780

Reviewed By: zixuan-wu

Differential Revison: https://reviews.llvm.org/D154588

Try to break a multiplication with a specific immediate to
an/a addition/subtraction of left shifts.

Reviewed By: zixuan-wu

Differential Revision: https://reviews.llvm.org/D153106

Reviewed By: zixuan-wu

Differential Revision: https://reviews.llvm.org/D153105