[llvm] [LV][VPlan] Add initial support for CSA vectorization (PR #106560)

[Ramkumar Ramachandra via llvm-commits]

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@@ -0,0 +1,73 @@
+//=== llvm/Analysis/CSADescriptors.cpp - CSA Descriptors -*- 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
+//
+//===----------------------------------------------------------------------===//
+//
+// This file "describes" conditional scalar assignments (CSA).
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Analysis/CSADescriptors.h"
+#include "llvm/IR/PatternMatch.h"
+#include "llvm/IR/Type.h"
+
+using namespace llvm;
+using namespace llvm::PatternMatch;
+
+#define DEBUG_TYPE "csa-descriptors"
+
+CSADescriptor CSADescriptor::isCSAPhi(PHINode *Phi, Loop *TheLoop) {
+  // Return CSADescriptor that describes a CSA that matches one of these
+  // patterns:
+  //   phi loop_inv, (select cmp, value, phi)
+  //   phi loop_inv, (select cmp, phi, value)
+  //   phi (select cmp, value, phi), loop_inv
+  //   phi (select cmp, phi, value), loop_inv
+  // If the CSA does not match any of these paterns, return a CSADescriptor
+  // that describes an InvalidCSA.
+
+  // Must be a scalar
+  Type *Type = Phi->getType();
+  if (!Type->isIntegerTy() && !Type->isFloatingPointTy() &&
+      !Type->isPointerTy())
+    return CSADescriptor();
+
+  // Match phi loop_inv, (select cmp, value, phi)
+  //    or phi loop_inv, (select cmp, phi, value)
+  //    or phi (select cmp, value, phi), loop_inv
+  //    or phi (select cmp, phi, value), loop_inv
+  if (Phi->getNumIncomingValues() != 2)
+    return CSADescriptor();
+  auto SelectInstIt = find_if(Phi->incoming_values(), [&Phi](Use &U) {
+    return match(U.get(), m_Select(m_Value(), m_Specific(Phi), m_Value())) ||
+           match(U.get(), m_Select(m_Value(), m_Value(), m_Specific(Phi)));
+  });
+  if (SelectInstIt == Phi->incoming_values().end())
+    return CSADescriptor();
+  auto LoopInvIt = find_if(Phi->incoming_values(), [&](Use &U) {
+    return U.get() != *SelectInstIt && TheLoop->isLoopInvariant(U.get());
+  });
+  if (LoopInvIt == Phi->incoming_values().end())
+    return CSADescriptor();
+
+  // Phi or Sel must be used only outside the loop,
+  // excluding if Phi use Sel or Sel use Phi
+  auto IsOnlyUsedOutsideLoop = [=](Value *V, Value *Ignore) {
+    return all_of(V->users(), [Ignore, TheLoop](User *U) {
+      if (U == Ignore)
+        return true;
+      if (auto *I = dyn_cast<Instruction>(U))
+        return !TheLoop->contains(I);
+      return true;
+    });
+  };
+  auto *Sel = cast<SelectInst>(SelectInstIt->get());
+  auto *LoopInv = LoopInvIt->get();
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artagnon wrote:

s/auto/Instruction/, since it's unclear from context?

https://github.com/llvm/llvm-project/pull/106560