[NFC][SCEV] Piping to pass new SCEVCheapExpansionBudget option into SCEVExpander::isHighCostExpansionHelper()

Summary:
In future patches`SCEVExpander::isHighCostExpansionHelper()` will respect the budget allocated by performing TTI cost modelling.
This is a fully NFC patch to make things reviewable.

Reviewers: reames, mkazantsev, wmi, sanjoy

Reviewed By: mkazantsev

Subscribers: hiraditya, zzheng, javed.absar, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D73705

llvm/include/llvm/Analysis/ScalarEvolutionExpander.h

@@ -19,11 +19,13 @@
 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
 #include "llvm/Analysis/ScalarEvolutionNormalization.h"
 #include "llvm/Analysis/TargetFolder.h"
+#include "llvm/Analysis/TargetTransformInfo.h"
 #include "llvm/IR/IRBuilder.h"
 #include "llvm/IR/ValueHandle.h"
+#include "llvm/Support/CommandLine.h"
 
 namespace llvm {
-  class TargetTransformInfo;
+  extern cl::opt<unsigned> SCEVCheapExpansionBudget;
 
   /// Return true if the given expression is safe to expand in the sense that
   /// all materialized values are safe to speculate anywhere their operands are
@@ -177,11 +179,13 @@ namespace llvm {
     /// At is an optional parameter which specifies point in code where user is
     /// going to expand this expression. Sometimes this knowledge can lead to a
     /// more accurate cost estimation.
-    bool isHighCostExpansion(const SCEV *Expr, Loop *L,
+    bool isHighCostExpansion(const SCEV *Expr, Loop *L, unsigned Budget,
                              const TargetTransformInfo *TTI,
                              const Instruction *At = nullptr) {
       SmallPtrSet<const SCEV *, 8> Processed;
-      return isHighCostExpansionHelper(Expr, L, At, TTI, Processed);
+      int BudgetRemaining = Budget * TargetTransformInfo::TCC_Basic;
+      return isHighCostExpansionHelper(Expr, L, At, BudgetRemaining, TTI,
+                                       Processed);
     }
 
     /// This method returns the canonical induction variable of the specified
@@ -324,7 +328,7 @@ namespace llvm {
 
     /// Recursive helper function for isHighCostExpansion.
     bool isHighCostExpansionHelper(const SCEV *S, Loop *L,
-                                   const Instruction *At,
+                                   const Instruction *At, int &BudgetRemaining,
                                    const TargetTransformInfo *TTI,
                                    SmallPtrSetImpl<const SCEV *> &Processed);
 

llvm/lib/Analysis/ScalarEvolutionExpander.cpp

@@ -24,10 +24,17 @@
 #include "llvm/IR/LLVMContext.h"
 #include "llvm/IR/Module.h"
 #include "llvm/IR/PatternMatch.h"
+#include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
 
 using namespace llvm;
+
+cl::opt<unsigned> llvm::SCEVCheapExpansionBudget(
+    "scev-cheap-expansion-budget", cl::Hidden, cl::init(4),
+    cl::desc("When performing SCEV expansion only if it is cheap to do, this "
+             "controls the budget that is considered cheap (default = 4)"));
+
 using namespace PatternMatch;
 
 /// ReuseOrCreateCast - Arrange for there to be a cast of V to Ty at IP,
@@ -2129,7 +2136,7 @@ SCEVExpander::getRelatedExistingExpansion(const SCEV *S, const Instruction *At,
 }
 
 bool SCEVExpander::isHighCostExpansionHelper(
-    const SCEV *S, Loop *L, const Instruction *At,
+    const SCEV *S, Loop *L, const Instruction *At, int &BudgetRemaining,
     const TargetTransformInfo *TTI, SmallPtrSetImpl<const SCEV *> &Processed) {
   // If we can find an existing value for this scev available at the point "At"
   // then consider the expression cheap.
@@ -2143,13 +2150,13 @@ bool SCEVExpander::isHighCostExpansionHelper(
     return false;
   case scTruncate:
     return isHighCostExpansionHelper(cast<SCEVTruncateExpr>(S)->getOperand(), L,
-                                     At, TTI, Processed);
+                                     At, BudgetRemaining, TTI, Processed);
   case scZeroExtend:
     return isHighCostExpansionHelper(cast<SCEVZeroExtendExpr>(S)->getOperand(),
-                                     L, At, TTI, Processed);
+                                     L, At, BudgetRemaining, TTI, Processed);
   case scSignExtend:
     return isHighCostExpansionHelper(cast<SCEVSignExtendExpr>(S)->getOperand(),
-                                     L, At, TTI, Processed);
+                                     L, At, BudgetRemaining, TTI, Processed);
   }
 
   if (!Processed.insert(S).second)
@@ -2162,8 +2169,8 @@ bool SCEVExpander::isHighCostExpansionHelper(
     // lowered into a right shift.
     if (auto *SC = dyn_cast<SCEVConstant>(UDivExpr->getRHS()))
       if (SC->getAPInt().isPowerOf2()) {
-        if (isHighCostExpansionHelper(UDivExpr->getLHS(), L, At, TTI,
+        if (isHighCostExpansionHelper(UDivExpr->getLHS(), L, At,
-                                      Processed))
+                                      BudgetRemaining, TTI, Processed))
           return true;
         const DataLayout &DL =
             L->getHeader()->getParent()->getParent()->getDataLayout();
@@ -2200,7 +2207,7 @@ bool SCEVExpander::isHighCostExpansionHelper(
   // they are not too expensive rematerialize.
   if (const SCEVNAryExpr *NAry = dyn_cast<SCEVNAryExpr>(S)) {
     for (auto *Op : NAry->operands())
-      if (isHighCostExpansionHelper(Op, L, At, TTI, Processed))
+      if (isHighCostExpansionHelper(Op, L, At, BudgetRemaining, TTI, Processed))
         return true;
   }
 

llvm/lib/Transforms/Scalar/IndVarSimplify.cpp

@@ -2759,7 +2759,8 @@ bool IndVarSimplify::run(Loop *L) {
 
       // Avoid high cost expansions.  Note: This heuristic is questionable in
       // that our definition of "high cost" is not exactly principled.
-      if (Rewriter.isHighCostExpansion(ExitCount, L, TTI))
+      if (Rewriter.isHighCostExpansion(ExitCount, L, SCEVCheapExpansionBudget,
+                                       TTI))
         continue;
 
       // Check preconditions for proper SCEVExpander operation. SCEV does not

llvm/lib/Transforms/Utils/LoopUnrollRuntime.cpp

@@ -635,7 +635,8 @@ bool llvm::UnrollRuntimeLoopRemainder(
   const DataLayout &DL = Header->getModule()->getDataLayout();
   SCEVExpander Expander(*SE, DL, "loop-unroll");
   if (!AllowExpensiveTripCount &&
-      Expander.isHighCostExpansion(TripCountSC, L, TTI, PreHeaderBR)) {
+      Expander.isHighCostExpansion(TripCountSC, L, SCEVCheapExpansionBudget,
+                                   TTI, PreHeaderBR)) {
     LLVM_DEBUG(dbgs() << "High cost for expanding trip count scev!\n");
     return false;
   }

llvm/lib/Transforms/Utils/LoopUtils.cpp

@@ -1361,7 +1361,8 @@ int llvm::rewriteLoopExitValues(Loop *L, LoopInfo *LI, TargetLibraryInfo *TLI,
             hasHardUserWithinLoop(L, Inst))
           continue;
 
-        bool HighCost = Rewriter.isHighCostExpansion(ExitValue, L, TTI, Inst);
+        bool HighCost = Rewriter.isHighCostExpansion(
+            ExitValue, L, SCEVCheapExpansionBudget, TTI, Inst);
         Value *ExitVal = Rewriter.expandCodeFor(ExitValue, PN->getType(), Inst);
 
         LLVM_DEBUG(dbgs() << "rewriteLoopExitValues: AfterLoopVal = "

llvm/lib/Transforms/Utils/SimplifyIndVar.cpp

@@ -669,7 +669,7 @@ bool SimplifyIndvar::replaceIVUserWithLoopInvariant(Instruction *I) {
     return false;
 
   // Do not generate something ridiculous even if S is loop invariant.
-  if (Rewriter.isHighCostExpansion(S, L, TTI, I))
+  if (Rewriter.isHighCostExpansion(S, L, SCEVCheapExpansionBudget, TTI, I))
     return false;
 
   auto *IP = GetLoopInvariantInsertPosition(L, I);