[llvm] r296992 - [SCEV] Decrease the recursion threshold for CompareValueComplexity

[Sanjoy Das via llvm-commits]

Author: sanjoy
Date: Sun Mar  5 17:49:17 2017
New Revision: 296992

URL: http://llvm.org/viewvc/llvm-project?rev=296992&view=rev
Log:
[SCEV] Decrease the recursion threshold for CompareValueComplexity

Fixes PR32142.

r287232 accidentally increased the recursion threshold for
CompareValueComplexity from 2 to 32.  This change reverses that change
by introducing a separate flag for CompareValueComplexity's threshold.

Modified:
    llvm/trunk/lib/Analysis/ScalarEvolution.cpp
    llvm/trunk/unittests/Analysis/ScalarEvolutionTest.cpp

Modified: llvm/trunk/lib/Analysis/ScalarEvolution.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ScalarEvolution.cpp?rev=296992&r1=296991&r2=296992&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ScalarEvolution.cpp (original)
+++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp Sun Mar  5 17:49:17 2017
@@ -132,10 +132,15 @@ static cl::opt<unsigned> AddOpsInlineThr
     cl::desc("Threshold for inlining multiplication operands into a SCEV"),
     cl::init(500));
 
-static cl::opt<unsigned>
-    MaxCompareDepth("scalar-evolution-max-compare-depth", cl::Hidden,
-                    cl::desc("Maximum depth of recursive compare complexity"),
-                    cl::init(32));
+static cl::opt<unsigned> MaxSCEVCompareDepth(
+    "scalar-evolution-max-scev-compare-depth", cl::Hidden,
+    cl::desc("Maximum depth of recursive SCEV complexity comparisons"),
+    cl::init(32));
+
+static cl::opt<unsigned> MaxValueCompareDepth(
+    "scalar-evolution-max-value-compare-depth", cl::Hidden,
+    cl::desc("Maximum depth of recursive value complexity comparisons"),
+    cl::init(2));
 
 static cl::opt<unsigned>
     MaxAddExprDepth("scalar-evolution-max-addexpr-depth", cl::Hidden,
@@ -496,7 +501,7 @@ static int
 CompareValueComplexity(SmallSet<std::pair<Value *, Value *>, 8> &EqCache,
                        const LoopInfo *const LI, Value *LV, Value *RV,
                        unsigned Depth) {
-  if (Depth > MaxCompareDepth || EqCache.count({LV, RV}))
+  if (Depth > MaxValueCompareDepth || EqCache.count({LV, RV}))
     return 0;
 
   // Order pointer values after integer values. This helps SCEVExpander form
@@ -583,7 +588,7 @@ static int CompareSCEVComplexity(
   if (LType != RType)
     return (int)LType - (int)RType;
 
-  if (Depth > MaxCompareDepth || EqCacheSCEV.count({LHS, RHS}))
+  if (Depth > MaxSCEVCompareDepth || EqCacheSCEV.count({LHS, RHS}))
     return 0;
   // Aside from the getSCEVType() ordering, the particular ordering
   // isn't very important except that it's beneficial to be consistent,

Modified: llvm/trunk/unittests/Analysis/ScalarEvolutionTest.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/unittests/Analysis/ScalarEvolutionTest.cpp?rev=296992&r1=296991&r2=296992&view=diff
==============================================================================
--- llvm/trunk/unittests/Analysis/ScalarEvolutionTest.cpp (original)
+++ llvm/trunk/unittests/Analysis/ScalarEvolutionTest.cpp Sun Mar  5 17:49:17 2017
@@ -465,7 +465,7 @@ TEST_F(ScalarEvolutionsTest, Commutative
     });
 }
 
-TEST_F(ScalarEvolutionsTest, SCEVCompareComplexity) {
+TEST_F(ScalarEvolutionsTest, CompareSCEVComplexity) {
   FunctionType *FTy =
       FunctionType::get(Type::getVoidTy(Context), std::vector<Type *>(), false);
   Function *F = cast<Function>(M.getOrInsertFunction("f", FTy));
@@ -532,6 +532,42 @@ TEST_F(ScalarEvolutionsTest, SCEVCompare
   EXPECT_NE(nullptr, SE.getSCEV(Acc[0]));
 }
 
+TEST_F(ScalarEvolutionsTest, CompareValueComplexity) {
+  IntegerType *IntPtrTy = M.getDataLayout().getIntPtrType(Context);
+  PointerType *IntPtrPtrTy = IntPtrTy->getPointerTo();
+
+  FunctionType *FTy =
+      FunctionType::get(Type::getVoidTy(Context), {IntPtrTy, IntPtrTy}, false);
+  Function *F = cast<Function>(M.getOrInsertFunction("f", FTy));
+  BasicBlock *EntryBB = BasicBlock::Create(Context, "entry", F);
+
+  Value *X = &*F->arg_begin();
+  Value *Y = &*std::next(F->arg_begin());
+
+  const int ValueDepth = 10;
+  for (int i = 0; i < ValueDepth; i++) {
+    X = new LoadInst(new IntToPtrInst(X, IntPtrPtrTy, "", EntryBB), "",
+                     /*isVolatile*/ false, EntryBB);
+    Y = new LoadInst(new IntToPtrInst(Y, IntPtrPtrTy, "", EntryBB), "",
+                     /*isVolatile*/ false, EntryBB);
+  }
+
+  auto *MulA = BinaryOperator::CreateMul(X, Y, "", EntryBB);
+  auto *MulB = BinaryOperator::CreateMul(Y, X, "", EntryBB);
+  ReturnInst::Create(Context, nullptr, EntryBB);
+
+  // This test isn't checking for correctness.  Today making A and B resolve to
+  // the same SCEV would require deeper searching in CompareValueComplexity,
+  // which will slow down compilation.  However, this test can fail (with LLVM's
+  // behavior still being correct) if we ever have a smarter
+  // CompareValueComplexity that is both fast and more accurate.
+
+  ScalarEvolution SE = buildSE(*F);
+  auto *A = SE.getSCEV(MulA);
+  auto *B = SE.getSCEV(MulB);
+  EXPECT_NE(A, B);
+}
+
 TEST_F(ScalarEvolutionsTest, SCEVAddExpr) {
   Type *Ty32 = Type::getInt32Ty(Context);
   Type *ArgTys[] = {Type::getInt64Ty(Context), Ty32};