[PATCH] D33562: MachineLICM: Add new condition for hoisting of caller preserved registers

[Matthias Braun via Phabricator via llvm-commits]

MatzeB added inline comments.


================
Comment at: lib/CodeGen/MachineLICM.cpp:895-898
+        // If the physreg is known to always be caller saved/restored then
+        // this use is safe to hoist
+        if (TRI->isCallerPreservedPhysReg(Reg, *I.getParent()->getParent()))
+          continue;
----------------
lei wrote:
> MatzeB wrote:
> > Could you move this check below the !isConstantPhysReg check as I expect this to be a rare case.
> This needs to be above !isConstantPhysReg which is an early function exit check where as this is just an loop exit check.  MRI->isConstantPhysReg(X2) will return false which will cause this function to exit with false.  I could combine the two into:
> ```
>  if (!MRI->isConstantPhysReg(Reg) && !(TRI->isCallerPreservedPhysReg(Reg, *I.getParent()->getParent())))
>     return false;
> ```
yes of course, my point was to check the ConstantPhysReg condition first and then the isCallerPreservedPhysReg which this does fine.


https://reviews.llvm.org/D33562