[SCEV] Add m_scev_Trunc pattern matcher. (llvm#163169)

This patch adds a new m_scev_Trunc pattern matcher for SCEVTruncateExpr
and uses it in a few places to slightly simplify the code.

PR: llvm#163169
(cherry picked from commit bc4e14b)

Author: fhahn

llvm/include/llvm/Analysis/ScalarEvolutionPatternMatch.h

@@ -170,6 +170,12 @@ m_scev_PtrToInt(const Op0_t &Op0) {
   return SCEVUnaryExpr_match<SCEVPtrToIntExpr, Op0_t>(Op0);
 }
 
+template <typename Op0_t>
+inline SCEVUnaryExpr_match<SCEVTruncateExpr, Op0_t>
+m_scev_Trunc(const Op0_t &Op0) {
+  return m_scev_Unary<SCEVTruncateExpr>(Op0);
+}
+
 /// Match a binary SCEV.
 template <typename SCEVTy, typename Op0_t, typename Op1_t>
 struct SCEVBinaryExpr_match {

llvm/lib/Analysis/ScalarEvolution.cpp

@@ -5412,20 +5412,15 @@ static Type *isSimpleCastedPHI(const SCEV *Op, const SCEVUnknown *SymbolicPHI,
   if (SourceBits != NewBits)
     return nullptr;
 
-  const SCEVSignExtendExpr *SExt = dyn_cast<SCEVSignExtendExpr>(Op);
-  const SCEVZeroExtendExpr *ZExt = dyn_cast<SCEVZeroExtendExpr>(Op);
-  if (!SExt && !ZExt)
-    return nullptr;
-  const SCEVTruncateExpr *Trunc =
-      SExt ? dyn_cast<SCEVTruncateExpr>(SExt->getOperand())
-           : dyn_cast<SCEVTruncateExpr>(ZExt->getOperand());
-  if (!Trunc)
-    return nullptr;
-  const SCEV *X = Trunc->getOperand();
-  if (X != SymbolicPHI)
-    return nullptr;
-  Signed = SExt != nullptr;
-  return Trunc->getType();
+  if (match(Op, m_scev_SExt(m_scev_Trunc(m_scev_Specific(SymbolicPHI))))) {
+    Signed = true;
+    return cast<SCEVCastExpr>(Op)->getOperand()->getType();
+  }
+  if (match(Op, m_scev_ZExt(m_scev_Trunc(m_scev_Specific(SymbolicPHI))))) {
+    Signed = false;
+    return cast<SCEVCastExpr>(Op)->getOperand()->getType();
+  }
+  return nullptr;
 }
 
 static const Loop *isIntegerLoopHeaderPHI(const PHINode *PN, LoopInfo &LI) {
@@ -15371,20 +15366,18 @@ bool ScalarEvolution::matchURem(const SCEV *Expr, const SCEV *&LHS,
   // Try to match 'zext (trunc A to iB) to iY', which is used
   // for URem with constant power-of-2 second operands. Make sure the size of
   // the operand A matches the size of the whole expressions.
-  if (const auto *ZExt = dyn_cast<SCEVZeroExtendExpr>(Expr))
-    if (const auto *Trunc = dyn_cast<SCEVTruncateExpr>(ZExt->getOperand(0))) {
-      LHS = Trunc->getOperand();
-      // Bail out if the type of the LHS is larger than the type of the
-      // expression for now.
-      if (getTypeSizeInBits(LHS->getType()) >
-          getTypeSizeInBits(Expr->getType()))
-        return false;
-      if (LHS->getType() != Expr->getType())
-        LHS = getZeroExtendExpr(LHS, Expr->getType());
-      RHS = getConstant(APInt(getTypeSizeInBits(Expr->getType()), 1)
-                        << getTypeSizeInBits(Trunc->getType()));
-      return true;
-    }
+  if (match(Expr, m_scev_ZExt(m_scev_Trunc(m_SCEV(LHS))))) {
+    Type *TruncTy = cast<SCEVZeroExtendExpr>(Expr)->getOperand()->getType();
+    // Bail out if the type of the LHS is larger than the type of the
+    // expression for now.
+    if (getTypeSizeInBits(LHS->getType()) > getTypeSizeInBits(Expr->getType()))
+      return false;
+    if (LHS->getType() != Expr->getType())
+      LHS = getZeroExtendExpr(LHS, Expr->getType());
+    RHS = getConstant(APInt(getTypeSizeInBits(Expr->getType()), 1)
+                      << getTypeSizeInBits(TruncTy));
+    return true;
+  }
   const auto *Add = dyn_cast<SCEVAddExpr>(Expr);
   if (Add == nullptr || Add->getNumOperands() != 2)
     return false;