[PATCH] D73716: [SCEV] SCEVExpander::isHighCostExpansionHelper(): begin cost modelling - model cast cost

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri updated this revision to Diff 246502.
lebedev.ri added a comment.

Rebased, NFC.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D73716/new/

https://reviews.llvm.org/D73716

Files:
  llvm/include/llvm/Analysis/ScalarEvolutionExpander.h
  llvm/lib/Analysis/ScalarEvolutionExpander.cpp


Index: llvm/lib/Analysis/ScalarEvolutionExpander.cpp
===================================================================
--- llvm/lib/Analysis/ScalarEvolutionExpander.cpp
+++ llvm/lib/Analysis/ScalarEvolutionExpander.cpp
@@ -2138,6 +2138,9 @@
 bool SCEVExpander::isHighCostExpansionHelper(
     const SCEV *S, Loop *L, const Instruction *At, int &BudgetRemaining,
     const TargetTransformInfo &TTI, SmallPtrSetImpl<const SCEV *> &Processed) {
+  if (BudgetRemaining < 0)
+    return true; // Already run out of budget, give up.
+
   // Was the cost of expansion of this expression already accounted for?
   if (!Processed.insert(S).second)
     return false; // We have already accounted for this expression.
@@ -2153,17 +2156,26 @@
     return false; // Assume to be zero-cost.
   }
 
-  // Zero/One operand expressions
-  switch (S->getSCEVType()) {
-  case scTruncate:
-    return isHighCostExpansionHelper(cast<SCEVTruncateExpr>(S)->getOperand(), L,
-                                     At, BudgetRemaining, TTI, Processed);
-  case scZeroExtend:
-    return isHighCostExpansionHelper(cast<SCEVZeroExtendExpr>(S)->getOperand(),
-                                     L, At, BudgetRemaining, TTI, Processed);
-  case scSignExtend:
-    return isHighCostExpansionHelper(cast<SCEVSignExtendExpr>(S)->getOperand(),
-                                     L, At, BudgetRemaining, TTI, Processed);
+  if (auto *CastExpr = dyn_cast<SCEVCastExpr>(S)) {
+    unsigned Opcode;
+    switch (S->getSCEVType()) {
+    case scTruncate:
+      Opcode = Instruction::Trunc;
+      break;
+    case scZeroExtend:
+      Opcode = Instruction::ZExt;
+      break;
+    case scSignExtend:
+      Opcode = Instruction::SExt;
+      break;
+    default:
+      llvm_unreachable("There are no other cast types.");
+    }
+    const SCEV *Op = CastExpr->getOperand();
+    BudgetRemaining -=
+        TTI.getOperationCost(Opcode, S->getType(), Op->getType());
+    return isHighCostExpansionHelper(Op, L, At, BudgetRemaining, TTI,
+                                     Processed);
   }
 
 
Index: llvm/include/llvm/Analysis/ScalarEvolutionExpander.h
===================================================================
--- llvm/include/llvm/Analysis/ScalarEvolutionExpander.h
+++ llvm/include/llvm/Analysis/ScalarEvolutionExpander.h
@@ -173,8 +173,8 @@
       ChainedPhis.clear();
     }
 
-    /// Return true for expressions that may incur non-trivial cost to evaluate
-    /// at runtime.
+    /// Return true for expressions that can't be evaluated at runtime
+    /// within given \b Budget.
     ///
     /// 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


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