llvm中的立即数测试

Question

在LLVM中，我想测试LoopInfo pass 得到的trip count是否是立即数 数字。比如下面的循环

for(i=0; i<10; i++) { ... }

行程计数为 10，它是一个立即数。可以调用 Loop 的成员函数getTripCount() 来获取表示行程计数的Value。我怎样才能确定这个值是否是立即数？

Answer 1

使用 Scalar Evolution 分析提供的以下 getter：

unsigned ScalarEvolution::getSmallConstantTripCount(Loop *L, BasicBlock *ExitingBlock)

/// getSmallConstantTripCount - Returns the maximum trip count of this loop as a
/// normal unsigned value. Returns 0 if the trip count is unknown or not
/// constant. Will also return 0 if the maximum trip count is very large (>=
/// 2^32).
///
/// This "trip count" assumes that control exits via ExitingBlock. More
/// precisely, it is the number of times that control may reach ExitingBlock
/// before taking the branch. For loops with multiple exits, it may not be the
/// number times that the loop header executes because the loop may exit
/// prematurely via another branch.