[PATCH] D34458: [TTI] Refine the cost of EXT in getUserCost()

[Haicheng Wu via Phabricator via llvm-commits]

haicheng added inline comments.


================
Comment at: llvm/trunk/include/llvm/CodeGen/BasicTTIImpl.h:167
+
+    return TargetTransformInfo::TCC_Basic;
+  }
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delena wrote:
> haicheng wrote:
> > delena wrote:
> > > At this point we should call to getOperationCost() and ask the target about the cost of Ext for the given type.
> > Sorry about the performance regression.
> > 
> > I think isExtFree(I) above checks isZExtFree() with its types.  The part that can affect x86 is isExtLoad().  Do you want me to add a target hook to choose use refined ext cost?
> First, I should understand why if the Src is not ExtLoad you return TargetTransformInfo::TCC_Basic.
> Why you are not asking the target about the actual cost of the Ext?
I think that getTLI()->isExtFree(I) above asks the actual cost of the Ext which is equivalent to calling getOperationCost() since they both check target specific isZExtFree() with type.


Repository:
  rL LLVM

https://reviews.llvm.org/D34458