[PATCH] D76847: [Target][ARM] Replace re-uses of old VPR values with VPNOTs

[Pierre van Houtryve via Phabricator via llvm-commits]

Pierre-vh marked 3 inline comments as done.
Pierre-vh added inline comments.


================
Comment at: llvm/lib/Target/ARM/MVEVPTOptimisationsPass.cpp:233
+    // on "VPNOTOperand".
+    for (MachineBasicBlock::instr_iterator Iter = ++Instr.getIterator();
+         Iter != MBB.end(); ++Iter) {
----------------
dmgreen wrote:
> Should this not be replacing _all_ uses of the old condition with the value from the VPNOT?
> 
> As in, if we see input code like:
> a = VCMP ..
> use(a)
> b = VPNOT a
> ..
> use(b)
> ..
> use(a)
> 
> Could it not be generally beneficial to insert a VPNOT between use of b and the second use of a? We could also probably have any amount of code between the predicated uses and it might still be beneficial, considering the costs of spills/reloads vs a single VPNOT.
I believe it's already doing that. I'll add more tests to show it.
I can certainly do the optimisation even outside blocks of predicated instruction, I just need to remove these lines and add a few tests:
``` 
   // Stop as soon as we leave the block of predicated instructions
      if (getVPTInstrPredicate(*Iter) == ARMVCC::None)
        break;
``` 


Repository:
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  https://reviews.llvm.org/D76847/new/

https://reviews.llvm.org/D76847