[llvm] [LoongArch] Optimize *W Instructions at MI level (PR #90463)

[Lu Weining via llvm-commits]

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+//===- LoongArchOptWInstrs.cpp - MI W instruction optimizations ----------===//
+//
+// 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 pass does some optimizations for *W instructions at the MI level.
+//
+// First it removes unneeded sext(addi.w rd, rs, 0) instructions. Either
+// because the sign extended bits aren't consumed or because the input was
+// already sign extended by an earlier instruction.
+//
+// Then:
+// 1. Unless explicit disabled or the target prefers instructions with W suffix,
+//    it removes the -w suffix from opw instructions whenever all users are
+//    dependent only on the lower word of the result of the instruction.
+//    The cases handled are:
+//    * addi.w because it helps reduce test differences between LA32 and LA64
+//      w/o being a pessimization.
+//
+// 2. Or if explicit enabled or the target prefers instructions with W suffix,
+//    it adds the W suffix to the instruction whenever all users are dependent
+//    only on the lower word of the result of the instruction.
+//    The cases handled are:
+//    * add.d/addi.d/sub.d/mul.d.
+//    * slli.d with imm < 32.
+//    * ld.d/ld.wu.
+//===---------------------------------------------------------------------===//
+
+#include "LoongArch.h"
+#include "LoongArchMachineFunctionInfo.h"
+#include "LoongArchSubtarget.h"
+#include "llvm/ADT/SmallSet.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/TargetInstrInfo.h"
+
+using namespace llvm;
+
+#define DEBUG_TYPE "loongarch-opt-w-instrs"
+#define LOONGARCH_OPT_W_INSTRS_NAME "LoongArch Optimize W Instructions"
+
+STATISTIC(NumRemovedSExtW, "Number of removed sign-extensions");
+STATISTIC(NumTransformedToWInstrs,
+          "Number of instructions transformed to W-ops");
+
+static cl::opt<bool> DisableSExtWRemoval("loongarch-disable-sextw-removal",
+                                         cl::desc("Disable removal of sext.w"),
+                                         cl::init(false), cl::Hidden);
+static cl::opt<bool> DisableStripWSuffix("loongarch-disable-strip-w-suffix",
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SixWeining wrote:

Seems that tests for this option are missing?

https://github.com/llvm/llvm-project/pull/90463