applyLoopGuards doesn't always preserve information when there are multiple assumes.
This patch tries to deal with multiple assumes regarding a SCEV's divisibility and min/max values, and rewrite it into a SCEV that still preserves all of the information.
For example, let the trip count of the loop be TC. Consider the 3 following assumes:
1. __builtin_assume(TC % 8 == 0);
2. __builtin_assume(TC > 0);
3. __builtin_assume(TC < 100);
Before this patch, depending on the assume processing order applyLoopGuards could create the following SCEV:
max(min((8 * (TC / 8)) , 99), 1)
Looking at this SCEV, it doesn't preserve the divisibility by 8 information.
After this patch, depending on the assume processing order applyLoopGuards could create the following SCEV:
max(min((8 * (TC / 8)) , 96), 8)
By aligning up 1 to 8, and aligning down 99 to 96, the new SCEV still preserves all of the original assumes.
Differential Revision: https://reviews.llvm.org/D144947
8e5aa969d0