[AArch64] Add an option for sve-prefer-fixed-over-scalable-if-equal. NFC

Add a new option to control preferFixedOverScalableIfEqualCost, useful for
testing.

Author: davemgreen

llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp

@@ -35,6 +35,9 @@ using namespace llvm::PatternMatch;
 static cl::opt<bool> EnableFalkorHWPFUnrollFix("enable-falkor-hwpf-unroll-fix",
                                                cl::init(true), cl::Hidden);
 
+static cl::opt<bool> SVEPreferFixedOverScalableIfEqualCost(
+    "sve-prefer-fixed-over-scalable-if-equal", cl::Hidden);
+
 static cl::opt<unsigned> SVEGatherOverhead("sve-gather-overhead", cl::init(10),
                                            cl::Hidden);
 
@@ -4919,6 +4922,12 @@ static bool containsDecreasingPointers(Loop *TheLoop,
   return false;
 }
 
+bool AArch64TTIImpl::preferFixedOverScalableIfEqualCost() const {
+  if (SVEPreferFixedOverScalableIfEqualCost.getNumOccurrences())
+    return SVEPreferFixedOverScalableIfEqualCost;
+  return ST->useFixedOverScalableIfEqualCost();
+}
+
 unsigned AArch64TTIImpl::getEpilogueVectorizationMinVF() const {
   return ST->getEpilogueVectorizationMinVF();
 }

llvm/lib/Target/AArch64/AArch64TargetTransformInfo.h

@@ -387,9 +387,7 @@ class AArch64TTIImpl : public BasicTTIImplBase<AArch64TTIImpl> {
     return TailFoldingStyle::DataWithoutLaneMask;
   }
 
-  bool preferFixedOverScalableIfEqualCost() const {
-    return ST->useFixedOverScalableIfEqualCost();
-  }
+  bool preferFixedOverScalableIfEqualCost() const;
 
   unsigned getEpilogueVectorizationMinVF() const;