[PATCH] Exit ScalarEvolution::getMulExpr Early when Choose Overflows

[Andrew Trick]

Comments could be a little more clear.

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Comment at: lib/Analysis/ScalarEvolution.cpp:2064-2070
@@ +2063,9 @@
+    // entering the loop by testing before the loop whether it will always
+    // overflow. Given that the loop below will compute:
+    // C(xe - 1, (xe - 1) / 2). Where:
+    // { xe = AddRec->getNumOperands() + OtherAddRec->getNumOperands() - 1 }
+    // and { OtherAddRec->getNumOperands() >= 0 } therefore:
+    // xe >= AddRec->getNumOperands() - 1
+    // Subsituting in the minimum xe:
+    // C(AddRec->getNumOperands() - 2, AddRec->getNumOperands() / 2 - 1)
+    // If Choose overflow for the expression above, then it will overflow in all
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I think this comment needs to be clarified.

The loop actually computes up to C(xe - 1, xe - 1) right?

We just happen to know that the Choose function's maximum is at C(xe - 1, (xe - 1) / 2). Let's make that explicit.

http://reviews.llvm.org/D5113