Don't brute-force analyze cubic or higher polynomials.

If this patch causes a performance regression for anyone, please let me know,
and it can be fixed in a different way with much more effort.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@59384 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp
index 3ff0935d8f3f8bfcd4bb271cfb786fa0a4e34a77..3f43a79bcae3ec3dde7538ba627c0699d987fe49 100644 (file)
--- a/lib/Analysis/ScalarEvolution.cpp
+++ b/lib/Analysis/ScalarEvolution.cpp
@@ -2967,27 +2967,6 @@ SCEVHandle SCEVAddRecExpr::getNumIterationsInRange(ConstantRange Range,
     }
   }
 
-  // Fallback, if this is a general polynomial, figure out the progression
-  // through brute force: evaluate until we find an iteration that fails the
-  // test.  This is likely to be slow, but getting an accurate trip count is
-  // incredibly important, we will be able to simplify the exit test a lot, and
-  // we are almost guaranteed to get a trip count in this case.
-  ConstantInt *TestVal = ConstantInt::get(getType(), 0);
-  ConstantInt *EndVal  = TestVal;  // Stop when we wrap around.
-  do {
-    ++NumBruteForceEvaluations;
-    SCEVHandle Val = evaluateAtIteration(SE.getConstant(TestVal), SE);
-    if (!isa<SCEVConstant>(Val))  // This shouldn't happen.
-      return new SCEVCouldNotCompute();
-
-    // Check to see if we found the value!
-    if (!Range.contains(cast<SCEVConstant>(Val)->getValue()->getValue()))
-      return SE.getConstant(TestVal);
-
-    // Increment to test the next index.
-    TestVal = ConstantInt::get(TestVal->getValue()+1);
-  } while (TestVal != EndVal);
-
   return new SCEVCouldNotCompute();
 }
 

diff --git a/test/Analysis/ScalarEvolution/2008-11-15-CubicOOM.ll b/test/Analysis/ScalarEvolution/2008-11-15-CubicOOM.ll
new file mode 100644 (file)
index 0000000..89e9efa
--- /dev/null
+++ b/test/Analysis/ScalarEvolution/2008-11-15-CubicOOM.ll
@@ -0,0 +1,19 @@
+; RUN: llvm-as < %s | opt -analyze -scalar-evolution
+; PR2602
+
+define i32 @a() nounwind  {
+entry:
+       br label %bb
+
+bb:            ; preds = %bb, %entry
+       %w.0 = phi i32 [ 0, %entry ], [ %tmp, %bb ]             ; <i32> [#uses=2]
+       %e.0 = phi i32 [ 0, %entry ], [ %e.1, %bb ]             ; <i32> [#uses=2]
+       %w.1 = add i32 0, %w.0          ; <i32>:0 [#uses=1]
+       %tmp = add i32 %e.0, %w.0               ; <i32>:1 [#uses=1]
+       %e.1 = add i32 %e.0, 1          ; <i32>:2 [#uses=1]
+       %cond = icmp eq i32 %w.1, -1            ; <i1>:3 [#uses=1]
+       br i1 %cond, label %return, label %bb
+
+return:                ; preds = %bb
+       ret i32 undef
+}