[PATCH] D33685: [InlineCost] Change CallAnalyzer::isGEPFree to use TTI::getUserCost instead of TTI::getGEPCost

[Evgeny Astigeevich via Phabricator via llvm-commits]

eastig created this revision.

Currently CallAnalyzer::isGEPFree uses TTI::getGEPCost to check if GEP is free. TTI::getGEPCost cannot handle cases when GEPs participate in Def-Use dependencies (see https://reviews.llvm.org/D31186 for example). There is TTI::getUserCost which can calculate the cost:

> int TargetTransformInfo::getUserCost	(const User * 	U)	const
>  Estimate the cost of a given IR user when lowered.
> 
> This can estimate the cost of either a ConstantExpr or Instruction when lowered. It has two primary advantages over the getOperationCost and getGEPCost above, and one significant disadvantage: it can only be used when the IR construct has already been formed.
> 
> The advantages are that it can inspect the SSA use graph to reason more accurately about the cost. For example, all-constant-GEPs can often be folded into a load or other instruction, but if they are used in some other context they may not be folded. This routine can distinguish such cases.
> 
> The returned cost is defined in terms of TargetCostConstants, see its comments for a detailed explanation of the cost values.

This patch gets CallAnalyzer::isGEPFree to use TTI::getUserCost instead of TTI::getGEPCost.


https://reviews.llvm.org/D33685

Files:
  lib/Analysis/InlineCost.cpp


Index: lib/Analysis/InlineCost.cpp
===================================================================
--- lib/Analysis/InlineCost.cpp
+++ lib/Analysis/InlineCost.cpp
@@ -350,9 +350,7 @@
        Indices.push_back(SimpleOp);
      else
        Indices.push_back(*I);
-  return TargetTransformInfo::TCC_Free ==
-         TTI.getGEPCost(GEP.getSourceElementType(), GEP.getPointerOperand(),
-                        Indices);
+  return TargetTransformInfo::TCC_Free == TTI.getUserCost(&GEP);
 }
 
 bool CallAnalyzer::visitAlloca(AllocaInst &I) {


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