[PATCH] D91125: [AArch64][GlobalISel] Port some AArch64 target specific MUL combines from SDAG.

[Jessica Paquette via Phabricator via llvm-commits]

paquette added inline comments.


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Comment at: llvm/lib/Target/AArch64/GISel/AArch64PostLegalizerCombiner.cpp:157
+      MachineInstr &UseMI = *MRI.use_instr_begin(Dst);
+      if (UseMI.getOpcode() == TargetOpcode::G_ADD ||
+          UseMI.getOpcode() == TargetOpcode::G_SUB)
----------------
aemerson wrote:
> paquette wrote:
> > Should this be conservative around G_ICMP as well? It can be selected using SUBS/ADDS.
> Can a G_MUL be folded into an icmp?
Oh, I guess not. There's no flag-setting variant of mul, so that wouldn't make sense. So it's fine, I think.


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Comment at: llvm/lib/Target/AArch64/GISel/AArch64PostLegalizerCombiner.cpp:225
+    }
+    // B.buildCopy(DstReg, Res.getReg(0));
+    Res->getOperand(0).setReg(DstReg);
----------------
aemerson wrote:
> paquette wrote:
> > Remove?
> This should probably actually be the copy, since we shouldn't be modifying an instruction without notifying the observer.
I guess ApplyFn could take in the observer as an argument, or `appleAArch64MulConstCombine` could notify the observer around the call?


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D91125/new/

https://reviews.llvm.org/D91125