[llvm] [NFC] [SPIRV] Add SPIRVCombinerHelper and refactor pre legalizer combiner to use it (PR #162735)

[Matt Arsenault via llvm-commits]

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@@ -0,0 +1,60 @@
+
+//===-- SPIRVCombinerHelper.cpp ---------------------------------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "SPIRVCombinerHelper.h"
+#include "llvm/CodeGen/GlobalISel/GenericMachineInstrs.h"
+#include "llvm/CodeGen/GlobalISel/MIPatternMatch.h"
+#include "llvm/IR/IntrinsicsSPIRV.h"
+#include "llvm/Target/TargetMachine.h"
+
+using namespace llvm;
+using namespace MIPatternMatch;
+
+SPIRVCombinerHelper::SPIRVCombinerHelper(
+    GISelChangeObserver &Observer, MachineIRBuilder &B, bool IsPreLegalize,
+    GISelValueTracking *VT, MachineDominatorTree *MDT, const LegalizerInfo *LI,
+    const SPIRVSubtarget &STI)
+    : CombinerHelper(Observer, B, IsPreLegalize, VT, MDT, LI), STI(STI) {}
+
+/// This match is part of a combine that
+/// rewrites length(X - Y) to distance(X, Y)
+///   (f32 (g_intrinsic length
+///           (g_fsub (vXf32 X) (vXf32 Y))))
+/// ->
+///   (f32 (g_intrinsic distance
+///           (vXf32 X) (vXf32 Y)))
+///
+bool SPIRVCombinerHelper::matchLengthToDistance(MachineInstr &MI) const {
+  if (MI.getOpcode() != TargetOpcode::G_INTRINSIC ||
+      cast<GIntrinsic>(MI).getIntrinsicID() != Intrinsic::spv_length)
+    return false;
+
+  // First operand of MI is `G_INTRINSIC` so start at operand 2.
+  Register SubReg = MI.getOperand(2).getReg();
+  MachineInstr *SubInstr = MRI.getVRegDef(SubReg);
+  if (!SubInstr || SubInstr->getOpcode() != TargetOpcode::G_FSUB)
+    return false;
+
+  return true;
+}
+void SPIRVCombinerHelper::applySPIRVDistance(MachineInstr &MI) const {
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arsenm wrote:

You should be able to move this to tablegen 

https://github.com/llvm/llvm-project/pull/162735