[llvm] Add late optimization pass for riscv (PR #117060)

[Craig Topper via llvm-commits]

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@@ -0,0 +1,157 @@
+//===-- RISCVLatePeephole.cpp - Late stage peephole optimization ----------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// This file provides RISC-V specific target descriptions.
+///
+//===----------------------------------------------------------------------===//
+
+#include "MCTargetDesc/RISCVMCTargetDesc.h"
+#include "RISCV.h"
+#include "RISCVInstrInfo.h"
+#include "RISCVSubtarget.h"
+#include "llvm/CodeGen/MachineBasicBlock.h"
+#include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
+#include "llvm/CodeGen/MachineDominators.h"
+#include "llvm/CodeGen/MachineInstrBuilder.h"
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/CodeGen/RegisterScavenging.h"
+#include "llvm/MC/TargetRegistry.h"
+#include "llvm/Support/Debug.h"
+
+using namespace llvm;
+
+#define DEBUG_TYPE "riscv-late-peephole"
+#define RISCV_LATE_PEEPHOLE_NAME "RISC-V Late Stage Peephole"
+
+namespace {
+
+struct RISCVLatePeepholeOpt : public MachineFunctionPass {
+  static char ID;
+
+  RISCVLatePeepholeOpt() : MachineFunctionPass(ID) {}
+
+  StringRef getPassName() const override { return RISCV_LATE_PEEPHOLE_NAME; }
+
+  void getAnalysisUsage(AnalysisUsage &AU) const override {
+    AU.addRequired<MachineDominatorTreeWrapperPass>();
+    AU.addPreserved<MachineDominatorTreeWrapperPass>();
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topperc wrote:

What if we don't preserve the dominator tree? Do any passes use it after this?

https://github.com/llvm/llvm-project/pull/117060