[SCEV][NFC] Factor out common logic into a separate method

SCEV has multiple occurences of code when we need to prove some predicate on
every iteration of a loop and do it with invocations of couple `isLoopEntryGuardedByCond`,
`isLoopBackedgeGuardedByCond`. This patch factors out these two calls into a separate
method. It is a preparation step to extend this logic: it is not the only way how we can prove
such conditions.

Differential Revision: https://reviews.llvm.org/D43373


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@325745 91177308-0d34-0410-b5e6-96231b3b80d8

Author: Max Kazantsev

include/llvm/Analysis/ScalarEvolution.h

@@ -834,6 +834,11 @@ class ScalarEvolution {
   bool isKnownPredicate(ICmpInst::Predicate Pred, const SCEV *LHS,
                         const SCEV *RHS);
 
+  /// Test if the condition described by Pred, LHS, RHS is known to be true on
+  /// every iteration of the loop of the recurrency LHS.
+  bool isKnownOnEveryIteration(ICmpInst::Predicate Pred,
+                               const SCEVAddRecExpr *LHS, const SCEV *RHS);
+
   /// Return true if, for all loop invariant X, the predicate "LHS `Pred` X"
   /// is monotonically increasing or decreasing.  In the former case set
   /// `Increasing` to true and in the latter case set `Increasing` to false.

lib/Analysis/ScalarEvolution.cpp

@@ -1732,9 +1732,7 @@ ScalarEvolution::getZeroExtendExpr(const SCEV *Op, Type *Ty, unsigned Depth) {
           const SCEV *N = getConstant(APInt::getMinValue(BitWidth) -
                                       getUnsignedRangeMax(Step));
           if (isLoopBackedgeGuardedByCond(L, ICmpInst::ICMP_ULT, AR, N) ||
-              (isLoopEntryGuardedByCond(L, ICmpInst::ICMP_ULT, Start, N) &&
-               isLoopBackedgeGuardedByCond(L, ICmpInst::ICMP_ULT,
-                                           AR->getPostIncExpr(*this), N))) {
+              isKnownOnEveryIteration(ICmpInst::ICMP_ULT, AR, N)) {
             // Cache knowledge of AR NUW, which is propagated to this
             // AddRec.
             const_cast<SCEVAddRecExpr *>(AR)->setNoWrapFlags(SCEV::FlagNUW);
@@ -1749,9 +1747,7 @@ ScalarEvolution::getZeroExtendExpr(const SCEV *Op, Type *Ty, unsigned Depth) {
           const SCEV *N = getConstant(APInt::getMaxValue(BitWidth) -
                                       getSignedRangeMin(Step));
           if (isLoopBackedgeGuardedByCond(L, ICmpInst::ICMP_UGT, AR, N) ||
-              (isLoopEntryGuardedByCond(L, ICmpInst::ICMP_UGT, Start, N) &&
-               isLoopBackedgeGuardedByCond(L, ICmpInst::ICMP_UGT,
-                                           AR->getPostIncExpr(*this), N))) {
+              isKnownOnEveryIteration(ICmpInst::ICMP_UGT, AR, N)) {
             // Cache knowledge of AR NW, which is propagated to this
             // AddRec.  Negative step causes unsigned wrap, but it
             // still can't self-wrap.
@@ -1994,9 +1990,7 @@ ScalarEvolution::getSignExtendExpr(const SCEV *Op, Type *Ty, unsigned Depth) {
             getSignedOverflowLimitForStep(Step, &Pred, this);
         if (OverflowLimit &&
             (isLoopBackedgeGuardedByCond(L, Pred, AR, OverflowLimit) ||
-             (isLoopEntryGuardedByCond(L, Pred, Start, OverflowLimit) &&
-              isLoopBackedgeGuardedByCond(L, Pred, AR->getPostIncExpr(*this),
-                                          OverflowLimit)))) {
+             isKnownOnEveryIteration(Pred, AR, OverflowLimit))) {
           // Cache knowledge of AR NSW, then propagate NSW to the wide AddRec.
           const_cast<SCEVAddRecExpr *>(AR)->setNoWrapFlags(SCEV::FlagNSW);
           return getAddRecExpr(
@@ -8677,17 +8671,16 @@ bool ScalarEvolution::isKnownPredicate(ICmpInst::Predicate Pred,
   if (LAR) {
     const Loop *L = LAR->getLoop();
     if (isAvailableAtLoopEntry(RHS, L) &&
-        isLoopEntryGuardedByCond(L, Pred, LAR->getStart(), RHS) &&
-        isLoopBackedgeGuardedByCond(L, Pred, LAR->getPostIncExpr(*this), RHS)) {
+        isKnownOnEveryIteration(Pred, LAR, RHS)) {
       if (!RAR) return true;
       LeftGuarded = true;
     }
   }
   if (RAR) {
     const Loop *L = RAR->getLoop();
+    auto SwappedPred = ICmpInst::getSwappedPredicate(Pred);
     if (isAvailableAtLoopEntry(LHS, L) &&
-        isLoopEntryGuardedByCond(L, Pred, LHS, RAR->getStart()) &&
-        isLoopBackedgeGuardedByCond(L, Pred, LHS, RAR->getPostIncExpr(*this))) {
+        isKnownOnEveryIteration(SwappedPred, RAR, LHS)) {
       if (!LAR) return true;
       RightGuarded = true;
     }
@@ -8702,6 +8695,14 @@ bool ScalarEvolution::isKnownPredicate(ICmpInst::Predicate Pred,
   return isKnownViaNonRecursiveReasoning(Pred, LHS, RHS);
 }
 
+bool ScalarEvolution::isKnownOnEveryIteration(ICmpInst::Predicate Pred,
+                                              const SCEVAddRecExpr *LHS,
+                                              const SCEV *RHS) {
+  const Loop *L = LHS->getLoop();
+  return isLoopEntryGuardedByCond(L, Pred, LHS->getStart(), RHS) &&
+         isLoopBackedgeGuardedByCond(L, Pred, LHS->getPostIncExpr(*this), RHS);
+}
+
 bool ScalarEvolution::isMonotonicPredicate(const SCEVAddRecExpr *LHS,
                                            ICmpInst::Predicate Pred,
                                            bool &Increasing) {