[PATCH] D35990: [SCEV] Prohibit SCEV transformations for huge SCEVs

[Max Kazantsev via Phabricator via llvm-commits]

mkazantsev updated this revision to Diff 183271.
mkazantsev added a comment.

Added comments.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D35990/new/

https://reviews.llvm.org/D35990

Files:
  lib/Analysis/ScalarEvolution.cpp
  test/Transforms/LoopStrengthReduce/X86/bin_power.ll


Index: test/Transforms/LoopStrengthReduce/X86/bin_power.ll
===================================================================
--- test/Transforms/LoopStrengthReduce/X86/bin_power.ll
+++ test/Transforms/LoopStrengthReduce/X86/bin_power.ll
@@ -1,4 +1,4 @@
-; RUN: opt < %s -loop-reduce -S | FileCheck %s
+; RUN: opt < %s -scalar-evolution-huge-expr-threshold=1000000 -loop-reduce -S | FileCheck %s
 
 target datalayout = "e-m:e-i32:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"
Index: lib/Analysis/ScalarEvolution.cpp
===================================================================
--- lib/Analysis/ScalarEvolution.cpp
+++ lib/Analysis/ScalarEvolution.cpp
@@ -211,6 +211,11 @@
                   cl::desc("Max coefficients in AddRec during evolving"),
                   cl::init(8));
 
+static cl::opt<unsigned>
+    HugeExprThreshold("scalar-evolution-huge-expr-threshold", cl::Hidden,
+                  cl::desc("Size of the expression which is considered huge"),
+                  cl::init(4096));
+
 //===----------------------------------------------------------------------===//
 //                           SCEV class definitions
 //===----------------------------------------------------------------------===//
@@ -845,6 +850,17 @@
   return F.Size;
 }
 
+/// Returns true if the subtree of \p S contains more than HugeExprThreshold
+/// nodes.
+static bool isHugeExpression(const SCEV *S) {
+  return S->getExpressionSize() >= HugeExprThreshold;
+}
+
+/// Returns true of \p Ops contains a huge SCEV (see definition above).
+static bool hasHugeExpression(SmallVectorImpl<const SCEV *> &Ops) {
+  return any_of(Ops, isHugeExpression);
+}
+
 namespace {
 
 struct SCEVDivision : public SCEVVisitor<SCEVDivision, void> {
@@ -2404,7 +2420,7 @@
   }
 
   // Limit recursion calls depth.
-  if (Depth > MaxArithDepth)
+  if (Depth > MaxArithDepth || hasHugeExpression(Ops))
     return getOrCreateAddExpr(Ops, Flags);
 
   // Okay, check to see if the same value occurs in the operand list more than
@@ -2883,7 +2899,7 @@
   Flags = StrengthenNoWrapFlags(this, scMulExpr, Ops, Flags);
 
   // Limit recursion calls depth.
-  if (Depth > MaxArithDepth)
+  if (Depth > MaxArithDepth || hasHugeExpression(Ops))
     return getOrCreateMulExpr(Ops, Flags);
 
   // If there are any constants, fold them together.
@@ -3056,7 +3072,8 @@
       // Limit max number of arguments to avoid creation of unreasonably big
       // SCEVAddRecs with very complex operands.
       if (AddRec->getNumOperands() + OtherAddRec->getNumOperands() - 1 >
-          MaxAddRecSize)
+          MaxAddRecSize || isHugeExpression(AddRec) ||
+          isHugeExpression(OtherAddRec))
         continue;
 
       bool Overflow = false;


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