[GlobalISel] Implement some binary reassociations, G_ADD for now

[aemerson]

Summary

- (op (op X, C1), C2) -> (op X, (op C1, C2))
- (op (op X, C1), Y) -> (op (op X, Y), C1)

Some code duplication with the G_PTR_ADD reassociations unfortunately but no
easy way to avoid it that I can see.

[aemerson]

@arsenm The AMDGPU/GlobalISel/regbankselect-amdgcn.s.buffer.load.ll test is failing but trying to run update_mir_test_checks.py fails with some error. Can you take a look to see if it's an issue with the test?

[paquette]

llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp

4517

might as well just return false here if !C1 to save a level of indentation

4530

maybe pull the MRI.hasOneNonDBGUse(Op00) in here and then we don't need the second if?

llvm/test/CodeGen/AArch64/GlobalISel/prelegalizer-combiner-binop-reassoc.mir

5

[aemerson]

llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp

4517

I actually left it like this to prepare for future reassociations that don't need C1 to match.

4530

Sure.

[aemerson]

Move a check.

[tschuett]

llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp

4519

Did you hoist C2out of the if for future work?

[aemerson]

llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp

4519

Actually it seems I misread the existing combines, these can be early exits.

[aemerson]

• Don't hoist a declaration.
• Rename Op00 like names to LHS/RHS ones.

[tschuett]

llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp

4519

Could you turn the auto's into bool's? C1 and C2 are know only for documentation?

[aemerson]

@arsenm ping. Do you know why the AMDGPU test doesn't work with update_mir_test_checks?

[arsenm]

In D150230#4344697, @aemerson wrote:

@arsenm ping. Do you know why the AMDGPU test doesn't work with update_mir_test_checks?

What is the error? update_mir_test_checks is pretty buggy with multiple run lines and multiple checks. I sometimes need to delete individual run lines to get it t work

llvm/test/CodeGen/AMDGPU/GlobalISel/llvm.amdgcn.s.buffer.load.ll

5019–5023

This result is worse so we'd ideally have something regbank aware

[aemerson]

Disable these combines for AMDGPU targets with the hook.

[arsenm]

llvm/lib/Target/AMDGPU/SIISelLowering.cpp

13441

Go with return true and leave the fixme? The diff was overall better I think

[aemerson]

Enable for AMDGPU.