[llvm] r276467 - [SCEV] Extract out a helper function; NFC

[Sanjoy Das via llvm-commits]

Author: sanjoy
Date: Fri Jul 22 15:47:55 2016
New Revision: 276467

URL: http://llvm.org/viewvc/llvm-project?rev=276467&view=rev
Log:
[SCEV] Extract out a helper function; NFC

The helper will get smarter in a later change, but right now this is
just code reorganization.

Modified:
    llvm/trunk/include/llvm/Analysis/ScalarEvolution.h
    llvm/trunk/lib/Analysis/ScalarEvolution.cpp

Modified: llvm/trunk/include/llvm/Analysis/ScalarEvolution.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Analysis/ScalarEvolution.h?rev=276467&r1=276466&r2=276467&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Analysis/ScalarEvolution.h (original)
+++ llvm/trunk/include/llvm/Analysis/ScalarEvolution.h Fri Jul 22 15:47:55 2016
@@ -1171,6 +1171,15 @@ namespace llvm {
     /// add recurrence on the loop \p L.
     bool isAddRecNeverPoison(const Instruction *I, const Loop *L);
 
+    /// Compute \p LHS - \p RHS and returns the result as an APInt if it is a
+    /// constant, and None if it isn't.
+    ///
+    /// This is intended to be a cheaper version of getMinusSCEV.  We can be
+    /// frugal here since we just bail out of actually constructing and
+    /// canonicalizing an expression in the cases where the result isn't going
+    /// to be a constant.
+    Optional<APInt> getConstantDifference(const SCEV *LHS, const SCEV *RHS);
+
   public:
     ScalarEvolution(Function &F, TargetLibraryInfo &TLI, AssumptionCache &AC,
                     DominatorTree &DT, LoopInfo &LI);

Modified: llvm/trunk/lib/Analysis/ScalarEvolution.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ScalarEvolution.cpp?rev=276467&r1=276466&r2=276467&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ScalarEvolution.cpp (original)
+++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp Fri Jul 22 15:47:55 2016
@@ -8578,6 +8578,16 @@ ScalarEvolution::isImpliedCondOperandsHe
   return false;
 }
 
+Optional<APInt> ScalarEvolution::getConstantDifference(const SCEV *LHS,
+                                                       const SCEV *RHS) {
+  if (const SCEVAddExpr *AddLHS = dyn_cast<SCEVAddExpr>(LHS))
+    if (AddLHS->getOperand(1) == RHS)
+      if (auto *Addend = dyn_cast<SCEVConstant>(AddLHS->getOperand(0)))
+        return Addend->getAPInt();
+
+  return None;
+}
+
 bool ScalarEvolution::isImpliedCondOperandsViaRanges(ICmpInst::Predicate Pred,
                                                      const SCEV *LHS,
                                                      const SCEV *RHS,
@@ -8588,9 +8598,8 @@ bool ScalarEvolution::isImpliedCondOpera
     // reduce the compile time impact of this optimization.
     return false;
 
-  const SCEVAddExpr *AddLHS = dyn_cast<SCEVAddExpr>(LHS);
-  if (!AddLHS || AddLHS->getOperand(1) != FoundLHS ||
-      !isa<SCEVConstant>(AddLHS->getOperand(0)))
+  Optional<APInt> Addend = getConstantDifference(LHS, FoundLHS);
+  if (!Addend)
     return false;
 
   APInt ConstFoundRHS = cast<SCEVConstant>(FoundRHS)->getAPInt();
@@ -8600,10 +8609,8 @@ bool ScalarEvolution::isImpliedCondOpera
   ConstantRange FoundLHSRange =
       ConstantRange::makeAllowedICmpRegion(Pred, ConstFoundRHS);
 
-  // Since `LHS` is `FoundLHS` + `AddLHS->getOperand(0)`, we can compute a range
-  // for `LHS`:
-  APInt Addend = cast<SCEVConstant>(AddLHS->getOperand(0))->getAPInt();
-  ConstantRange LHSRange = FoundLHSRange.add(ConstantRange(Addend));
+  // Since `LHS` is `FoundLHS` + `Addend`, we can compute a range for `LHS`:
+  ConstantRange LHSRange = FoundLHSRange.add(ConstantRange(*Addend));
 
   // We can also compute the range of values for `LHS` that satisfy the
   // consequent, "`LHS` `Pred` `RHS`":