[all-commits] [llvm/llvm-project] 219ba2: [SCEV] Preserve divisibility and min/max informati...

[komalon1 via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 219ba2fb7b0ae89101f3c81a47fe4fc4aa80dea4
      https://github.com/llvm/llvm-project/commit/219ba2fb7b0ae89101f3c81a47fe4fc4aa80dea4
  Author: Alon Kom <alon.kom at mobileye.com>
  Date:   2023-02-23 (Thu, 23 Feb 2023)

  Changed paths:
    M llvm/lib/Analysis/ScalarEvolution.cpp
    M llvm/test/Analysis/ScalarEvolution/trip-multiple-guard-info.ll
    M llvm/unittests/Analysis/ScalarEvolutionTest.cpp

  Log Message:
  -----------
  [SCEV] Preserve divisibility and min/max information in applyLoopGuards

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/D141850