[llvm-commits] [llvm] r59384 - in /llvm/trunk: lib/Analysis/ScalarEvolution.cpp test/Analysis/ScalarEvolution/2008-11-15-CubicOOM.ll

[Nick Lewycky]

Author: nicholas
Date: Sat Nov 15 22:14:25 2008
New Revision: 59384

URL: http://llvm.org/viewvc/llvm-project?rev=59384&view=rev
Log:
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.

Added:
    llvm/trunk/test/Analysis/ScalarEvolution/2008-11-15-CubicOOM.ll
Modified:
    llvm/trunk/lib/Analysis/ScalarEvolution.cpp

Modified: llvm/trunk/lib/Analysis/ScalarEvolution.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ScalarEvolution.cpp?rev=59384&r1=59383&r2=59384&view=diff

==============================================================================
--- llvm/trunk/lib/Analysis/ScalarEvolution.cpp (original)
+++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp Sat Nov 15 22:14:25 2008
@@ -2967,27 +2967,6 @@
     }
   }
 
-  // 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();
 }
 

Added: llvm/trunk/test/Analysis/ScalarEvolution/2008-11-15-CubicOOM.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/ScalarEvolution/2008-11-15-CubicOOM.ll?rev=59384&view=auto

==============================================================================
--- llvm/trunk/test/Analysis/ScalarEvolution/2008-11-15-CubicOOM.ll (added)
+++ llvm/trunk/test/Analysis/ScalarEvolution/2008-11-15-CubicOOM.ll Sat Nov 15 22:14:25 2008
@@ -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
+}