[RISCV][EVL] Disable the EVLIndVarSimplify Pass by default

Author: arcbbb

llvm/lib/Target/RISCV/RISCVTargetMachine.cpp

@@ -114,6 +114,11 @@ static cl::opt<bool>
                            cl::desc("Enable Machine Pipeliner for RISC-V"),
                            cl::init(false), cl::Hidden);
 
+static cl::opt<bool>
+    EnableEVLIndVarSimplify("riscv-simplify-evl-iv",
+                            cl::desc("Enable the EVLIndVarSimplify pass."),
+                            cl::init(false), cl::Hidden);
+
 extern "C" LLVM_ABI LLVM_EXTERNAL_VISIBILITY void LLVMInitializeRISCVTarget() {
   RegisterTargetMachine<RISCVTargetMachine> X(getTheRISCV32Target());
   RegisterTargetMachine<RISCVTargetMachine> Y(getTheRISCV64Target());
@@ -645,7 +650,7 @@ void RISCVTargetMachine::registerPassBuilderCallbacks(PassBuilder &PB) {
 
   PB.registerVectorizerEndEPCallback(
       [](FunctionPassManager &FPM, OptimizationLevel Level) {
-        if (Level.isOptimizingForSpeed())
+        if (Level.isOptimizingForSpeed() && EnableEVLIndVarSimplify)
           FPM.addPass(createFunctionToLoopPassAdaptor(EVLIndVarSimplifyPass()));
       });
 }