[SCEV][IndVars] Always provide insertion point to the SCEVExpander::isHighCostExpansion()

Summary: This addresses the `llvm/test/Transforms/IndVarSimplify/elim-extend.ll` `@nestedIV` regression from D73728

Reviewers: reames, mkazantsev, wmi, sanjoy

Reviewed By: mkazantsev

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D73777

1 files changed, 8 insertions, 14 deletions

diff --git a/llvm/lib/Analysis/ScalarEvolutionExpander.cpp b/llvm/lib/Analysis/ScalarEvolutionExpander.cpp
index 65a88ea..a09f1f3 100644
--- a/llvm/lib/Analysis/ScalarEvolutionExpander.cpp
+++ b/llvm/lib/Analysis/ScalarEvolutionExpander.cpp
@@ -2136,7 +2136,7 @@ SCEVExpander::getRelatedExistingExpansion(const SCEV *S, const Instruction *At,
 }
 
 bool SCEVExpander::isHighCostExpansionHelper(
-    const SCEV *S, Loop *L, const Instruction *At, int &BudgetRemaining,
+    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.
@@ -2147,7 +2147,7 @@ bool SCEVExpander::isHighCostExpansionHelper(
 
   // If we can find an existing value for this scev available at the point "At"
   // then consider the expression cheap.
-  if (At && getRelatedExistingExpansion(S, At, L))
+  if (getRelatedExistingExpansion(S, &At, L))
     return false; // Consider the expression to be free.
 
   switch (S->getSCEVType()) {
@@ -2198,18 +2198,12 @@ bool SCEVExpander::isHighCostExpansionHelper(
     // UDiv from the user's code. If we can't find a UDiv in the code with some
     // simple searching, we need to account for it's cost.
 
-    BasicBlock *ExitingBB = L->getExitingBlock();
-    if (At || ExitingBB) {
-      if (!At)
-        At = &ExitingBB->back();
-
-      // At the beginning of this function we already tried to find existing
-      // value for plain 'S'. Now try to lookup 'S + 1' since it is common
-      // pattern involving division. This is just a simple search heuristic.
-      if (getRelatedExistingExpansion(
-              SE.getAddExpr(S, SE.getConstant(S->getType(), 1)), At, L))
-        return false; // Consider it to be free.
-    }
+    // At the beginning of this function we already tried to find existing
+    // value for plain 'S'. Now try to lookup 'S + 1' since it is common
+    // pattern involving division. This is just a simple search heuristic.
+    if (getRelatedExistingExpansion(
+            SE.getAddExpr(S, SE.getConstant(S->getType(), 1)), &At, L))
+      return false; // Consider it to be free.
 
     // Need to count the cost of this UDiv.
     BudgetRemaining -= TTI.getOperationCost(Instruction::UDiv, S->getType());