[LV] Remove EVLIndVarSimplify pass

Initially this was needed to replace the fixed-step canonical IV with the variable-step EVL IV, but this was eventually superseded by the loop vectorizer doing this transform itself in llvm#147222. The pass was then removed from the RISC-V pipeline in llvm#151483 and the loop vectorizer stopped emitting the metadata used by the pass in llvm#155760, so now there's no users of it.

Author: lukel97

llvm/include/llvm/Transforms/Vectorize/EVLIndVarSimplify.h

@@ -375,7 +375,6 @@
 #include "llvm/Transforms/Utils/SymbolRewriter.h"
 #include "llvm/Transforms/Utils/UnifyFunctionExitNodes.h"
 #include "llvm/Transforms/Utils/UnifyLoopExits.h"
-#include "llvm/Transforms/Vectorize/EVLIndVarSimplify.h"
 #include "llvm/Transforms/Vectorize/LoadStoreVectorizer.h"
 #include "llvm/Transforms/Vectorize/LoopIdiomVectorize.h"
 #include "llvm/Transforms/Vectorize/LoopVectorize.h"

llvm/lib/Passes/PassBuilder.cpp

@@ -755,7 +755,6 @@ LOOP_ANALYSIS("should-run-extra-simple-loop-unswitch",
 #endif
 LOOP_PASS("canon-freeze", CanonicalizeFreezeInLoopsPass())
 LOOP_PASS("dot-ddg", DDGDotPrinterPass())
-LOOP_PASS("evl-iv-simplify", EVLIndVarSimplifyPass())
 LOOP_PASS("guard-widening", GuardWideningPass())
 LOOP_PASS("extra-simple-loop-unswitch-passes",
           ExtraLoopPassManager<ShouldRunExtraSimpleLoopUnswitch>())

llvm/lib/Passes/PassRegistry.def

@@ -1,5 +1,4 @@
 add_llvm_component_library(LLVMVectorize
-  EVLIndVarSimplify.cpp
   LoadStoreVectorizer.cpp
   LoopIdiomVectorize.cpp
   LoopVectorizationLegality.cpp