[SCEV] Add initial pattern matching for SCEV constants. (NFC) (#119389)

Add initial pattern matching for SCEV constants. Follow-up patches will
add additional matchers for various SCEV expressions.

This patch only converts a few instances to use the new matchers to make
sure everything builds as expected for now.

PR: #119389

Author: fhahn

llvm/include/llvm/Analysis/ScalarEvolutionPatternMatch.h

@@ -0,0 +1,58 @@
+//===----------------------------------------------------------------------===//
+// 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 a simple and efficient mechanism for performing general
+// tree-based pattern matches on SCEVs, based on LLVM's IR pattern matchers.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ANALYSIS_SCALAREVOLUTIONPATTERNMATCH_H
+#define LLVM_ANALYSIS_SCALAREVOLUTIONPATTERNMATCH_H
+
+#include "llvm/Analysis/ScalarEvolutionExpressions.h"
+
+namespace llvm {
+namespace SCEVPatternMatch {
+
+template <typename Val, typename Pattern>
+bool match(const SCEV *S, const Pattern &P) {
+  return P.match(S);
+}
+
+template <typename Predicate> struct cst_pred_ty : public Predicate {
+  bool match(const SCEV *S) {
+    assert((isa<SCEVCouldNotCompute>(S) || !S->getType()->isVectorTy()) &&
+           "no vector types expected from SCEVs");
+    auto *C = dyn_cast<SCEVConstant>(S);
+    return C && this->isValue(C->getAPInt());
+  }
+};
+
+struct is_zero {
+  bool isValue(const APInt &C) { return C.isZero(); }
+};
+/// Match an integer 0.
+inline cst_pred_ty<is_zero> m_scev_Zero() { return cst_pred_ty<is_zero>(); }
+
+struct is_one {
+  bool isValue(const APInt &C) { return C.isOne(); }
+};
+/// Match an integer 1.
+inline cst_pred_ty<is_one> m_scev_One() { return cst_pred_ty<is_one>(); }
+
+struct is_all_ones {
+  bool isValue(const APInt &C) { return C.isAllOnes(); }
+};
+/// Match an integer with all bits set.
+inline cst_pred_ty<is_all_ones> m_scev_AllOnes() {
+  return cst_pred_ty<is_all_ones>();
+}
+
+} // namespace SCEVPatternMatch
+} // namespace llvm
+
+#endif

llvm/lib/Analysis/ScalarEvolution.cpp

@@ -79,6 +79,7 @@
 #include "llvm/Analysis/LoopInfo.h"
 #include "llvm/Analysis/MemoryBuiltins.h"
 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
+#include "llvm/Analysis/ScalarEvolutionPatternMatch.h"
 #include "llvm/Analysis/TargetLibraryInfo.h"
 #include "llvm/Analysis/ValueTracking.h"
 #include "llvm/Config/llvm-config.h"
@@ -133,6 +134,7 @@
 
 using namespace llvm;
 using namespace PatternMatch;
+using namespace SCEVPatternMatch;
 
 #define DEBUG_TYPE "scalar-evolution"
 
@@ -443,23 +445,11 @@ ArrayRef<const SCEV *> SCEV::operands() const {
   llvm_unreachable("Unknown SCEV kind!");
 }
 
-bool SCEV::isZero() const {
-  if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(this))
-    return SC->getValue()->isZero();
-  return false;
-}
+bool SCEV::isZero() const { return match(this, m_scev_Zero()); }
 
-bool SCEV::isOne() const {
-  if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(this))
-    return SC->getValue()->isOne();
-  return false;
-}
+bool SCEV::isOne() const { return match(this, m_scev_One()); }
 
-bool SCEV::isAllOnesValue() const {
-  if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(this))
-    return SC->getValue()->isMinusOne();
-  return false;
-}
+bool SCEV::isAllOnesValue() const { return match(this, m_scev_AllOnes()); }
 
 bool SCEV::isNonConstantNegative() const {
   const SCEVMulExpr *Mul = dyn_cast<SCEVMulExpr>(this);
@@ -3423,9 +3413,8 @@ const SCEV *ScalarEvolution::getUDivExpr(const SCEV *LHS,
     return S;
 
   // 0 udiv Y == 0
-  if (const SCEVConstant *LHSC = dyn_cast<SCEVConstant>(LHS))
-    if (LHSC->getValue()->isZero())
-      return LHS;
+  if (match(LHS, m_scev_Zero()))
+    return LHS;
 
   if (const SCEVConstant *RHSC = dyn_cast<SCEVConstant>(RHS)) {
     if (RHSC->getValue()->isOne())
@@ -10593,7 +10582,6 @@ ScalarEvolution::ExitLimit ScalarEvolution::howFarToZero(const SCEV *V,
   // Get the initial value for the loop.
   const SCEV *Start = getSCEVAtScope(AddRec->getStart(), L->getParentLoop());
   const SCEV *Step = getSCEVAtScope(AddRec->getOperand(1), L->getParentLoop());
-  const SCEVConstant *StepC = dyn_cast<SCEVConstant>(Step);
 
   if (!isLoopInvariant(Step, L))
     return getCouldNotCompute();
@@ -10615,8 +10603,8 @@ ScalarEvolution::ExitLimit ScalarEvolution::howFarToZero(const SCEV *V,
   // Handle unitary steps, which cannot wraparound.
   // 1*N = -Start; -1*N = Start (mod 2^BW), so:
   //   N = Distance (as unsigned)
-  if (StepC &&
-      (StepC->getValue()->isOne() || StepC->getValue()->isMinusOne())) {
+
+  if (match(Step, m_CombineOr(m_scev_One(), m_scev_AllOnes()))) {
     APInt MaxBECount = getUnsignedRangeMax(applyLoopGuards(Distance, Guards));
     MaxBECount = APIntOps::umin(MaxBECount, getUnsignedRangeMax(Distance));
 
@@ -10668,6 +10656,7 @@ ScalarEvolution::ExitLimit ScalarEvolution::howFarToZero(const SCEV *V,
   }
 
   // Solve the general equation.
+  const SCEVConstant *StepC = dyn_cast<SCEVConstant>(Step);
   if (!StepC || StepC->getValue()->isZero())
     return getCouldNotCompute();
   const SCEV *E = SolveLinEquationWithOverflow(
@@ -15510,9 +15499,7 @@ void ScalarEvolution::LoopGuards::collectFromBlock(
 
     // If we have LHS == 0, check if LHS is computing a property of some unknown
     // SCEV %v which we can rewrite %v to express explicitly.
-    const SCEVConstant *RHSC = dyn_cast<SCEVConstant>(RHS);
-    if (Predicate == CmpInst::ICMP_EQ && RHSC &&
-        RHSC->getValue()->isNullValue()) {
+    if (Predicate == CmpInst::ICMP_EQ && match(RHS, m_scev_Zero())) {
       // If LHS is A % B, i.e. A % B == 0, rewrite A to (A /u B) * B to
       // explicitly express that.
       const SCEV *URemLHS = nullptr;
@@ -15693,8 +15680,7 @@ void ScalarEvolution::LoopGuards::collectFromBlock(
           To = RHS;
         break;
       case CmpInst::ICMP_NE:
-        if (isa<SCEVConstant>(RHS) &&
-            cast<SCEVConstant>(RHS)->getValue()->isNullValue()) {
+        if (match(RHS, m_scev_Zero())) {
           const SCEV *OneAlignedUp =
               DividesBy ? GetNextSCEVDividesByDivisor(One, DividesBy) : One;
           To = SE.getUMaxExpr(FromRewritten, OneAlignedUp);