[PATCH] D73777: [SCEV][IndVars] Always provide insertion point to the SCEVExpander::isHighCostExpansion()

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri updated this revision to Diff 242597.
lebedev.ri added a comment.

Rebased.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D73777/new/

https://reviews.llvm.org/D73777

Files:
  llvm/include/llvm/Analysis/ScalarEvolutionExpander.h
  llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
  llvm/test/Transforms/IndVarSimplify/elim-extend.ll


Index: llvm/test/Transforms/IndVarSimplify/elim-extend.ll
===================================================================
--- llvm/test/Transforms/IndVarSimplify/elim-extend.ll
+++ llvm/test/Transforms/IndVarSimplify/elim-extend.ll
@@ -140,8 +140,8 @@
 ; CHECK-NEXT:    store i8 0, i8* [[ADR2]]
 ; CHECK-NEXT:    [[ADR3:%.*]] = getelementptr i8, i8* [[ADDRESS]], i64 [[INDVARS_IV_NEXT]]
 ; CHECK-NEXT:    store i8 0, i8* [[ADR3]]
-; CHECK-NEXT:    [[INNERCMP:%.*]] = icmp sgt i64 [[TMP0]], [[INDVARS_IV_NEXT]]
-; CHECK-NEXT:    br i1 [[INNERCMP]], label [[INNERLOOP]], label [[INNEREXIT:%.*]]
+; CHECK-NEXT:    [[EXITCOND:%.*]] = icmp ne i64 [[INDVARS_IV_NEXT]], [[TMP0]]
+; CHECK-NEXT:    br i1 [[EXITCOND]], label [[INNERLOOP]], label [[INNEREXIT:%.*]]
 ; CHECK:       innerexit:
 ; CHECK-NEXT:    [[TMP4:%.*]] = trunc i64 [[TMP0]] to i32
 ; CHECK-NEXT:    br label [[OUTERMERGE]]
@@ -153,8 +153,8 @@
 ; CHECK-NEXT:    [[ADR5:%.*]] = getelementptr i8, i8* [[ADDRESS]], i64 [[OFS5]]
 ; CHECK-NEXT:    store i8 0, i8* [[ADR5]]
 ; CHECK-NEXT:    [[INDVARS_IV_NEXT2]] = add nuw nsw i64 [[INDVARS_IV1]], 1
-; CHECK-NEXT:    [[EXITCOND:%.*]] = icmp ne i64 [[INDVARS_IV_NEXT2]], [[WIDE_TRIP_COUNT]]
-; CHECK-NEXT:    br i1 [[EXITCOND]], label [[OUTERLOOP]], label [[RETURN:%.*]]
+; CHECK-NEXT:    [[EXITCOND4:%.*]] = icmp ne i64 [[INDVARS_IV_NEXT2]], [[WIDE_TRIP_COUNT]]
+; CHECK-NEXT:    br i1 [[EXITCOND4]], label [[OUTERLOOP]], label [[RETURN:%.*]]
 ; CHECK:       return:
 ; CHECK-NEXT:    ret void
 ;
Index: llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
+++ llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -2719,6 +2719,9 @@
   // If we have a trip count expression, rewrite the loop's exit condition
   // using it.
   if (!DisableLFTR) {
+    BasicBlock *PreHeader = L->getLoopPreheader();
+    BranchInst *PreHeaderBR = cast<BranchInst>(PreHeader->getTerminator());
+
     SmallVector<BasicBlock*, 16> ExitingBlocks;
     L->getExitingBlocks(ExitingBlocks);
     for (BasicBlock *ExitingBB : ExitingBlocks) {
@@ -2753,7 +2756,7 @@
       // 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, SCEVCheapExpansionBudget,
-                                       TTI))
+                                       TTI, PreHeaderBR))
         continue;
 
       // Check preconditions for proper SCEVExpander operation. SCEV does not
Index: llvm/include/llvm/Analysis/ScalarEvolutionExpander.h
===================================================================
--- llvm/include/llvm/Analysis/ScalarEvolutionExpander.h
+++ llvm/include/llvm/Analysis/ScalarEvolutionExpander.h
@@ -176,12 +176,12 @@
     /// 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
-    /// more accurate cost estimation.
+    /// At is a parameter which specifies point in code where user is going to
+    /// expand this expression. Sometimes this knowledge can lead to
+    /// a less pessimistic cost estimation.
     bool isHighCostExpansion(const SCEV *Expr, Loop *L, unsigned Budget,
                              const TargetTransformInfo *TTI,
-                             const Instruction *At = nullptr) {
+                             const Instruction *At) {
       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.


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