[PATCH] D98791: [PowerPC][NFC] Do not enter prefix selection if it cannot do better.

[Stefan Pintilie via Phabricator via llvm-commits]

stefanp added inline comments.


================
Comment at: llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp:1174
+  // selection used one instruction we cannot do better.
+  if (Subtarget.hasPrefixInstrs() && InstCntDirect != 1) {
     unsigned InstCntDirectP = 0;
----------------
NeHuang wrote:
> Please correct me if I my understand is wrong here. It seems to me `InstCntDirect=1` case has been covered in the check below.
> ```   
>  // If the prefix and non-prefix cases use the same number of instructions
> // we will prefer the non-prefix case.
>     if (ResultP && (!Result || InstCntDirectP < InstCntDirect))
> ```
> Then intention of adding an early exit for `InstCntDirect == 1` case is to save the trial of calling `selectI64ImmDirectPrefix` and further checks below. 
Yes that is correct. There is no need to call `selectI64ImmDirectPrefix` if we already know that it will fail the check `InstCntDirectP < InstCntDirect` and that the result it produces won't be used.


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  https://reviews.llvm.org/D98791/new/

https://reviews.llvm.org/D98791