[PATCH] D35027: [PowerPC] Reduce register pressure by not materializing a constant just for use as an index register for X-Form loads/stores

[Stefan Pintilie via Phabricator via llvm-commits]

stefanp added inline comments.


================
Comment at: lib/Target/PowerPC/PPCISelLowering.cpp:2247
+      (!(isIntS16Immediate(N.getOperand(1), imm) &&
+         N.getOperand(1).hasOneUse() && N.getOperand(0).hasOneUse()))) {
     Base = N.getOperand(0);
----------------
stefanp wrote:
> Do we need `N.getOperand(1)` to have only one use?
> For example: 
> ```
> r10 = (generate r10 somehow)
> ADD r4 = r3 + r10  (Is ADD, is not immed S16, r3 has one use, BUT r10 has two uses)
> LD r5 = (0, r4)
> ADD r7 = r6 + r10 
> LD r8 = (0, r7)
> ```
> Ideally I think we can get rid of those ADDs from above. 
> There may be a case I'm not thinking of here. 
Sorry... I made a mistake with that last comment.
Ok, so I mixed up the location of the NOT in that if statement.

It may be clearer if instead of `! ( COND && COND && COND)` it's `!COND || !COND || !COND`. 
At least it may be clearer in my head...

Either way, I'll have to go back and look at this again. 



https://reviews.llvm.org/D35027