Let LLVMOpLowering specify a PatternBenefit - NFC

Currently the benefit is always set to 1 which limits the ability to do A->B->C lowering

PiperOrigin-RevId: 264854146

mlir/include/mlir/Conversion/StandardToLLVM/ConvertStandardToLLVM.h

@@ -116,7 +116,7 @@ private:
 class LLVMOpLowering : public ConversionPattern {
 public:
   LLVMOpLowering(StringRef rootOpName, MLIRContext *context,
-                 LLVMTypeConverter &lowering);
+                 LLVMTypeConverter &lowering, PatternBenefit benefit = 1);
 
 protected:
   // Back-reference to the lowering class, used to call type and function

mlir/lib/Conversion/StandardToLLVM/ConvertStandardToLLVM.cpp

@@ -193,9 +193,9 @@ static Type getMemRefElementPtrType(MemRefType t, LLVMTypeConverter &lowering) {
 }
 
 LLVMOpLowering::LLVMOpLowering(StringRef rootOpName, MLIRContext *context,
-                               LLVMTypeConverter &lowering_)
-    : ConversionPattern(rootOpName, /*benefit=*/1, context),
-      lowering(lowering_) {}
+                               LLVMTypeConverter &lowering_,
+                               PatternBenefit benefit)
+    : ConversionPattern(rootOpName, benefit, context), lowering(lowering_) {}
 
 namespace {
 // Base class for Standard to LLVM IR op conversions.  Matches the Op type