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

[Javed Absar via llvm-commits]

javed.absar added inline comments.


================
Comment at: lib/Target/ARM/ARMISelLowering.cpp:11608
+  }
+  return -1;
+}
----------------
rengolin wrote:
> I guess -1 here means illegal, though without seeing the code that is using it, I can't assume.
You are right. The same is mentioned in Analysis/TargetTransformInfo.h wherein it is stated "If the AM is not supported, it returns a negative value". 


================
Comment at: lib/Target/ARM/ARMISelLowering.h:299
+    /// If the AM is not supported, the return value must be negative.
+    int getScalingFactorCost(const DataLayout &DL, const AddrMode &AM, Type *Ty,
+                             unsigned AS) const override;
----------------
rengolin wrote:
> Where is this being used?
It is used in LoopStrengthReduce, where decisions to transform a loop is taken based on a cost-model that takes scaling-factor cost into consideration. 


https://reviews.llvm.org/D24857