[PATCH] [TTI/CostModel] improve TTI::getGEPCost and use it in CostModel::getInstructionCost

[Jingyue Wu]

================
Comment at: include/llvm/Analysis/TargetTransformInfoImpl.h:392
@@ +391,3 @@
+  unsigned getGEPCost(const Value *Ptr, ArrayRef<Value *> Operands) {
+    const GlobalValue *BaseGV = dyn_cast<GlobalValue>(Ptr);
+    bool HasBaseReg = (BaseGV == nullptr);
----------------
hfinkel wrote:
> hfinkel wrote:
> > You should call stripPointerCasts before doing the dyn_cast.
> Should be dyn_cast_or_null b/c the cost model should not require the base pointer be known when estimating costs.
Interesting -- when Ptr == nullptr, what is a good estimation? Fall back to using `getAddressComputationCost`?

http://reviews.llvm.org/D9819

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