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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
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@ -2967,27 +2967,6 @@ SCEVHandle SCEVAddRecExpr::getNumIterationsInRange(ConstantRange Range,
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}
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}
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// Fallback, if this is a general polynomial, figure out the progression
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// through brute force: evaluate until we find an iteration that fails the
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// test. This is likely to be slow, but getting an accurate trip count is
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// incredibly important, we will be able to simplify the exit test a lot, and
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// we are almost guaranteed to get a trip count in this case.
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ConstantInt *TestVal = ConstantInt::get(getType(), 0);
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ConstantInt *EndVal = TestVal; // Stop when we wrap around.
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do {
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++NumBruteForceEvaluations;
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SCEVHandle Val = evaluateAtIteration(SE.getConstant(TestVal), SE);
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if (!isa<SCEVConstant>(Val)) // This shouldn't happen.
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return new SCEVCouldNotCompute();
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// Check to see if we found the value!
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if (!Range.contains(cast<SCEVConstant>(Val)->getValue()->getValue()))
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return SE.getConstant(TestVal);
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// Increment to test the next index.
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TestVal = ConstantInt::get(TestVal->getValue()+1);
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} while (TestVal != EndVal);
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return new SCEVCouldNotCompute();
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}
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19
test/Analysis/ScalarEvolution/2008-11-15-CubicOOM.ll
Normal file
19
test/Analysis/ScalarEvolution/2008-11-15-CubicOOM.ll
Normal file
@ -0,0 +1,19 @@
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; RUN: llvm-as < %s | opt -analyze -scalar-evolution
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; PR2602
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define i32 @a() nounwind {
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entry:
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br label %bb
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bb: ; preds = %bb, %entry
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%w.0 = phi i32 [ 0, %entry ], [ %tmp, %bb ] ; <i32> [#uses=2]
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%e.0 = phi i32 [ 0, %entry ], [ %e.1, %bb ] ; <i32> [#uses=2]
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%w.1 = add i32 0, %w.0 ; <i32>:0 [#uses=1]
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%tmp = add i32 %e.0, %w.0 ; <i32>:1 [#uses=1]
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%e.1 = add i32 %e.0, 1 ; <i32>:2 [#uses=1]
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%cond = icmp eq i32 %w.1, -1 ; <i1>:3 [#uses=1]
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br i1 %cond, label %return, label %bb
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return: ; preds = %bb
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ret i32 undef
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}
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