Extended Description

I encountered an assertion failure in scalar evolutions:

opt: ScalarEvolution.cpp:2362: llvm::SCEVHandle
llvm::SCEVAddRecExpr::getNumIterationsInRange(llvm::ConstantRange, bool) const:
Assertion `isa(ExitValue) && "Constant folding of integers not
implemented?"' failed.

The assertion has found a real problem. The line in question is
"ConstantExpr::getSDiv(ExitValue, A);" where ExitValue is i32 0 and A is i32 -1.
getSDiv eventually gets into this case in ConstantFoldBinaryInstruction
(ConstantFolding.cpp):

00572 case Instruction::SDiv:
00573 if (CI2->isNullValue()) return 0; // X / 0 -> can't fold
00574 if (CI2->isAllOnesValue() &&
00575 (((CI1->getType()->getPrimitiveSizeInBits() == 64) &&
00576 (CI1->getSExtValue() == INT64_MIN)) ||
00577 (CI1->getSExtValue() == -CI1->getSExtValue())))
00578 return 0; // MIN_INT / -1 -> overflow
00579 return ConstantInt::get(C1->getType(),
00580 CI1->getSExtValue() / CI2->getSExtValue());

Given that CI1 is the left hand side, CI1->getSExtValue() ==
-CI1->getSExtValue() when the left is 0.

This code also fails to properly fold arbitrary precision integers, so it
deserves to be rewritten.