[PATCH] D24857: [ARM] Assign cost of scaling used in addressing mode for ARM cores

[James Molloy via llvm-commits]

jmolloy added inline comments.


================
Comment at: lib/Target/ARM/ARMISelLowering.cpp:11604
+  if (isLegalAddressingMode(DL, AM, Ty, AS)) {
+    if (Subtarget->hasFPAO())
+      return AM.Scale < 0 ? 1 : 0; // positive offsets execute faster
----------------
rengolin wrote:
> This is not really a cost model... but I don't have a better idea. This is a very specific feature.
> 
> @jmolloy, are you happy with this?
I know you asked for it to be a feature flag, but... I'm not particularly keen on it as a feature flag. Are we moving towards feature flags for cost model decisions now? :/

Wouldn't something like:

   switch (Subtarget->getCPUName()) {
   default: return 0;
   case Cortex-R52:
      return AM.Scale < 0 ? 1 : 0;
   }

be alright? It's more cost-model-like...


https://reviews.llvm.org/D24857