[AMDGPU] Basic implementation of isExtractSubvectorCheap

Add a basic implementation of isExtractSubvectorCheap that only
considers extracts at offset 0.

Differential Revision: https://reviews.llvm.org/D127385

diff --git a/llvm/lib/Target/AMDGPU/SIISelLowering.cpp b/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
index 8abc1bc..12a6f4f 100644 (file)
--- a/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
+++ b/llvm/lib/Target/AMDGPU/SIISelLowering.cpp
@@ -1581,6 +1581,15 @@ bool SITargetLowering::shouldConvertConstantLoadToIntImm(const APInt &Imm,
   return true;
 }
 
+bool SITargetLowering::isExtractSubvectorCheap(EVT ResVT, EVT SrcVT,
+                                               unsigned Index) const {
+  if (!isOperationLegalOrCustom(ISD::EXTRACT_SUBVECTOR, ResVT))
+    return false;
+
+  // TODO: Add more cases that are cheap.
+  return Index == 0;
+}
+
 bool SITargetLowering::isTypeDesirableForOp(unsigned Op, EVT VT) const {
   if (Subtarget->has16BitInsts() && VT == MVT::i16) {
     switch (Op) {

diff --git a/llvm/lib/Target/AMDGPU/SIISelLowering.h b/llvm/lib/Target/AMDGPU/SIISelLowering.h
index 25fe8c0..16f944f 100644 (file)
--- a/llvm/lib/Target/AMDGPU/SIISelLowering.h
+++ b/llvm/lib/Target/AMDGPU/SIISelLowering.h
@@ -321,6 +321,9 @@ public:
   bool shouldConvertConstantLoadToIntImm(const APInt &Imm,
                                         Type *Ty) const override;
 
+  bool isExtractSubvectorCheap(EVT ResVT, EVT SrcVT,
+                               unsigned Index) const override;
+
   bool isTypeDesirableForOp(unsigned Op, EVT VT) const override;
 
   bool isOffsetFoldingLegal(const GlobalAddressSDNode *GA) const override;