[PATCH] D146102: [TTI] Add X86 target specific version of getPointersChainCost.

[Valeriy Dmitriev via Phabricator via llvm-commits]

vdmitrie created this revision.
vdmitrie added reviewers: RKSimon, ABataev.
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When all the pointers are off the same base address and have known
distances to each other these differences can be encoded into displacements
in x86 arch. So the only cost that matters is cost of the base GEP.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D146102

Files:
  llvm/lib/Target/X86/X86TargetTransformInfo.cpp
  llvm/lib/Target/X86/X86TargetTransformInfo.h
  llvm/test/Transforms/SLPVectorizer/X86/remark_horcost.ll
  llvm/test/Transforms/SLPVectorizer/X86/remark_not_all_parts.ll


Index: llvm/test/Transforms/SLPVectorizer/X86/remark_not_all_parts.ll
===================================================================
--- llvm/test/Transforms/SLPVectorizer/X86/remark_not_all_parts.ll
+++ llvm/test/Transforms/SLPVectorizer/X86/remark_not_all_parts.ll
@@ -62,7 +62,7 @@
   ; YAML-NEXT: Function:        foo
   ; YAML-NEXT: Args:
   ; YAML-NEXT:   - String:          'Stores SLP vectorized with cost '
-  ; YAML-NEXT:   - Cost:            '-4'
+  ; YAML-NEXT:   - Cost:            '-1'
   ; YAML-NEXT:   - String:          ' and with tree size '
   ; YAML-NEXT:   - TreeSize:        '4'
 
Index: llvm/test/Transforms/SLPVectorizer/X86/remark_horcost.ll
===================================================================
--- llvm/test/Transforms/SLPVectorizer/X86/remark_horcost.ll
+++ llvm/test/Transforms/SLPVectorizer/X86/remark_horcost.ll
@@ -86,7 +86,7 @@
   ; YAML-NEXT: Function:        foo
   ; YAML-NEXT: Args:
   ; YAML-NEXT:   - String:          'Stores SLP vectorized with cost '
-  ; YAML-NEXT:   - Cost:            '-14'
+  ; YAML-NEXT:   - Cost:            '-5'
   ; YAML-NEXT:   - String:          ' and with tree size '
   ; YAML-NEXT:   - TreeSize:        '4'
 
Index: llvm/lib/Target/X86/X86TargetTransformInfo.h
===================================================================
--- llvm/lib/Target/X86/X86TargetTransformInfo.h
+++ llvm/lib/Target/X86/X86TargetTransformInfo.h
@@ -177,6 +177,10 @@
                                          Align Alignment,
                                          TTI::TargetCostKind CostKind,
                                          const Instruction *I);
+  InstructionCost getPointersChainCost(ArrayRef<const Value *> Ptrs,
+                                       const Value *Base,
+                                       const TTI::PointersChainInfo &Info,
+                                       TTI::TargetCostKind CostKind);
   InstructionCost getAddressComputationCost(Type *PtrTy, ScalarEvolution *SE,
                                             const SCEV *Ptr);
 
Index: llvm/lib/Target/X86/X86TargetTransformInfo.cpp
===================================================================
--- llvm/lib/Target/X86/X86TargetTransformInfo.cpp
+++ llvm/lib/Target/X86/X86TargetTransformInfo.cpp
@@ -4899,6 +4899,23 @@
   return Cost + LT.first;
 }
 
+InstructionCost X86TTIImpl::getPointersChainCost(
+    ArrayRef<const Value *> Ptrs, const Value *Base,
+    const TTI::PointersChainInfo &Info, TTI::TargetCostKind CostKind) {
+  if (Info.isSameBase() && Info.isKnownStride()) {
+    // If all the pointers have known stride all the differences are translated
+    // into constants. X86 memory addressing allows encoding it into
+    // displacement. So we just need to take the base GEP cost.
+    if (const auto *BaseGEP = dyn_cast<GetElementPtrInst>(Base)) {
+      SmallVector<const Value *> Indices(BaseGEP->indices());
+      return getGEPCost(BaseGEP->getSourceElementType(),
+                        BaseGEP->getPointerOperand(), Indices, CostKind);
+    }
+    return TTI::TCC_Free;
+  }
+  return BaseT::getPointersChainCost(Ptrs, Base, Info, CostKind);
+}
+
 InstructionCost X86TTIImpl::getAddressComputationCost(Type *Ty,
                                                       ScalarEvolution *SE,
                                                       const SCEV *Ptr) {


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