[PATCH] D35664: [SCEV] Limit max size of AddRecExpr during evolving

[Max Kazantsev via Phabricator via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rL308847: [SCEV] Limit max size of AddRecExpr during evolving (authored by mkazantsev).

Changed prior to commit:
  https://reviews.llvm.org/D35664?vs=107457&id=107833#toc

Repository:
  rL LLVM

https://reviews.llvm.org/D35664

Files:
  llvm/trunk/lib/Analysis/ScalarEvolution.cpp
  llvm/trunk/test/Analysis/ScalarEvolution/max-addrec-size.ll


Index: llvm/trunk/test/Analysis/ScalarEvolution/max-addrec-size.ll
===================================================================
--- llvm/trunk/test/Analysis/ScalarEvolution/max-addrec-size.ll
+++ llvm/trunk/test/Analysis/ScalarEvolution/max-addrec-size.ll
@@ -0,0 +1,33 @@
+; RUN: opt -analyze -scalar-evolution -scalar-evolution-max-add-rec-size=3 < %s | FileCheck %s
+
+; Show that we are able to avoid creation of huge SCEVs by capping the max
+; AddRec size.
+define i32 @test_01(i32 %a, i32 %b) {
+
+; CHECK-LABEL: Classifying expressions for: @test_01
+; CHECK-NEXT:    %iv = phi i32 [ %a, %entry ], [ %iv.next, %loop ]
+; CHECK-NEXT:    -->  {%a,+,%b}<%loop> U: full-set S: full-set
+; CHECK-NEXT:    %iv.next = add i32 %iv, %b
+; CHECK-NEXT:    -->  {(%a + %b),+,%b}<%loop> U: full-set S: full-set
+; CHECK-NEXT:    %x1 = mul i32 %iv, %iv.next
+; CHECK-NEXT:    -->  {((%a + %b) * %a),+,(((2 * %a) + (2 * %b)) * %b),+,(2 * %b * %b)}<%loop> U: full-set S: full-set
+; CHECK-NEXT:    %x2 = mul i32 %x1, %x1
+; CHECK-NEXT:    -->  ({((%a + %b) * %a),+,(((2 * %a) + (2 * %b)) * %b),+,(2 * %b * %b)}<%loop> * {((%a + %b) * %a),+,(((2 * %a) + (2 * %b)) * %b),+,(2 * %b * %b)}<%loop>) U: full-set S: full-set
+; CHECK-NEXT:    %x3 = mul i32 %x2, %x1
+; CHECK-NEXT:    -->  ({((%a + %b) * %a),+,(((2 * %a) + (2 * %b)) * %b),+,(2 * %b * %b)}<%loop> * {((%a + %b) * %a),+,(((2 * %a) + (2 * %b)) * %b),+,(2 * %b * %b)}<%loop> * {((%a + %b) * %a),+,(((2 * %a) + (2 * %b)) * %b),+,(2 * %b * %b)}<%loop>) U: full-set S: full-set
+
+entry:
+  br label %loop
+
+loop:
+  %iv = phi i32 [ %a, %entry ], [ %iv.next, %loop ]
+  %iv.next = add i32 %iv, %b
+  %cond = icmp slt i32 %iv.next, 1000
+  br i1 %cond, label %loop, label %exit
+
+exit:
+  %x1 = mul i32 %iv, %iv.next
+  %x2 = mul i32 %x1, %x1
+  %x3 = mul i32 %x2, %x1
+  ret i32 %x3
+}
Index: llvm/trunk/lib/Analysis/ScalarEvolution.cpp
===================================================================
--- llvm/trunk/lib/Analysis/ScalarEvolution.cpp
+++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp
@@ -162,6 +162,11 @@
                 cl::desc("Maximum depth of recursive SExt/ZExt"),
                 cl::init(8));
 
+static cl::opt<unsigned>
+    MaxAddRecSize("scalar-evolution-max-add-rec-size", cl::Hidden,
+                  cl::desc("Max coefficients in AddRec during evolving"),
+                  cl::init(16));
+
 //===----------------------------------------------------------------------===//
 //                           SCEV class definitions
 //===----------------------------------------------------------------------===//
@@ -2878,6 +2883,12 @@
       if (!OtherAddRec || OtherAddRec->getLoop() != AddRecLoop)
         continue;
 
+      // Limit max number of arguments to avoid creation of unreasonably big
+      // SCEVAddRecs with very complex operands.
+      if (AddRec->getNumOperands() + OtherAddRec->getNumOperands() - 1 >
+          MaxAddRecSize)
+        continue;
+
       bool Overflow = false;
       Type *Ty = AddRec->getType();
       bool LargerThan64Bits = getTypeSizeInBits(Ty) > 64;


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