[AArch64] Add -aarch64-insert-extract-base-cost

The new flag -aarch64-insert-extract-base-cost can be used to
set the value of AArch64Subtarget::getVectorInsertExtractBaseCost(),
for the purposes of experimentation.

Differential Revision: https://reviews.llvm.org/D124835

Author: peterwaller-arm

llvm/lib/Target/AArch64/AArch64Subtarget.cpp

@@ -52,6 +52,16 @@ static cl::opt<bool>
 static cl::opt<bool> UseAA("aarch64-use-aa", cl::init(true),
                            cl::desc("Enable the use of AA during codegen."));
 
+static cl::opt<unsigned> OverrideVectorInsertExtractBaseCost(
+    "aarch64-insert-extract-base-cost",
+    cl::desc("Base cost of vector insert/extract element"), cl::Hidden);
+
+unsigned AArch64Subtarget::getVectorInsertExtractBaseCost() const {
+  if (OverrideVectorInsertExtractBaseCost.getNumOccurrences() > 0)
+    return OverrideVectorInsertExtractBaseCost;
+  return VectorInsertExtractBaseCost;
+}
+
 AArch64Subtarget &AArch64Subtarget::initializeSubtargetDependencies(
     StringRef FS, StringRef CPUString, StringRef TuneCPUString) {
   // Determine default and user-specified characteristics

llvm/lib/Target/AArch64/AArch64Subtarget.h

@@ -210,9 +210,7 @@ class AArch64Subtarget final : public AArch64GenSubtargetInfo {
   }
 
   unsigned getMaxInterleaveFactor() const { return MaxInterleaveFactor; }
-  unsigned getVectorInsertExtractBaseCost() const {
-    return VectorInsertExtractBaseCost;
-  }
+  unsigned getVectorInsertExtractBaseCost() const;
   unsigned getCacheLineSize() const override { return CacheLineSize; }
   unsigned getPrefetchDistance() const override { return PrefetchDistance; }
   unsigned getMinPrefetchStride(unsigned NumMemAccesses,