The recently announced IBM z17 processor implements the architecture
already supported as "arch15" in LLVM. This patch adds support for "z17"
as an alternate architecture name for arch15.
This patch also add the scheduler description for the z17 processor,
provided by Jonas Paulsson.
Detect (non-intrinsic) IR patterns corresponding to the semantics
of the various widening and high-word multiplication instructions.
Specifically, this is done by:
- Recognizing even/odd widening multiplication patterns in DAGCombine
- Recognizing widening multiply-and-add on top during ISel
- Implementing the standard MULHS/MUHLU IR opcodes
- Detecting high-word multiply-and-add (which common code does not)
Depending on architecture level, this can support all integer
vector types as well as the scalar i128 type.
Fixes: https://github.com/llvm/llvm-project/issues/129705
