From 2d8275d72e1602a1869e6286b0ffbf9034ab102b Mon Sep 17 00:00:00 2001
From: Roman Lebedev <lebedev.ri@gmail.com>
Date: Tue, 25 Feb 2020 21:51:12 +0300
Subject: [PATCH] [SCEV] SCEVExpander::isHighCostExpansion(): assert if TTI is
 not provided

Summary:
Currently, as per `check-llvm`, we never call `SCEVExpander::isHighCostExpansion()` with null TTI,
so this appears to be a safe restriction.

Reviewers: reames, mkazantsev, wmi, sanjoy

Reviewed By: mkazantsev

Subscribers: javed.absar, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D73712
---
 llvm/include/llvm/Analysis/ScalarEvolutionExpander.h |  7 +++++--
 llvm/lib/Analysis/ScalarEvolutionExpander.cpp        | 11 +++++++----
 2 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/llvm/include/llvm/Analysis/ScalarEvolutionExpander.h b/llvm/include/llvm/Analysis/ScalarEvolutionExpander.h
index a1b2ed3666c7..65f4a29888c6 100644
--- a/llvm/include/llvm/Analysis/ScalarEvolutionExpander.h
+++ b/llvm/include/llvm/Analysis/ScalarEvolutionExpander.h
@@ -182,9 +182,12 @@ namespace llvm {
     bool isHighCostExpansion(const SCEV *Expr, Loop *L, unsigned Budget,
                              const TargetTransformInfo *TTI,
                              const Instruction *At = nullptr) {
+      assert(TTI && "This function requires TTI to be provided.");
+      if (!TTI)      // In assert-less builds, avoid crashing
+        return true; // by always claiming to be high-cost.
       SmallPtrSet<const SCEV *, 8> Processed;
       int BudgetRemaining = Budget * TargetTransformInfo::TCC_Basic;
-      return isHighCostExpansionHelper(Expr, L, At, BudgetRemaining, TTI,
+      return isHighCostExpansionHelper(Expr, L, At, BudgetRemaining, *TTI,
                                        Processed);
     }
 
@@ -329,7 +332,7 @@ namespace llvm {
     /// Recursive helper function for isHighCostExpansion.
     bool isHighCostExpansionHelper(const SCEV *S, Loop *L,
                                    const Instruction *At, int &BudgetRemaining,
-                                   const TargetTransformInfo *TTI,
+                                   const TargetTransformInfo &TTI,
                                    SmallPtrSetImpl<const SCEV *> &Processed);
 
     /// Insert the specified binary operator, doing a small amount of work to
diff --git a/llvm/lib/Analysis/ScalarEvolutionExpander.cpp b/llvm/lib/Analysis/ScalarEvolutionExpander.cpp
index e8f267a39225..989e86485d62 100644
--- a/llvm/lib/Analysis/ScalarEvolutionExpander.cpp
+++ b/llvm/lib/Analysis/ScalarEvolutionExpander.cpp
@@ -2137,7 +2137,7 @@ SCEVExpander::getRelatedExistingExpansion(const SCEV *S, const Instruction *At,
 
 bool SCEVExpander::isHighCostExpansionHelper(
     const SCEV *S, Loop *L, const Instruction *At, int &BudgetRemaining,
-    const TargetTransformInfo *TTI, SmallPtrSetImpl<const SCEV *> &Processed) {
+    const TargetTransformInfo &TTI, SmallPtrSetImpl<const SCEV *> &Processed) {
   // 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.
@@ -2145,13 +2145,16 @@ 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))
-    return false;
+    return false; // Consider the expression to be free.
 
-  // Zero/One operand expressions
   switch (S->getSCEVType()) {
   case scUnknown:
   case scConstant:
-    return false;
+    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);
-- 
2.34.1