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f84407be32
make much more sense and in theory be more correct. If you trace the code alllll the way back to when it was first introduced, the comments make it slightly more clear what was going on here. At that time, the only way Base != V was if DL (then TD) was non-null. As a consequence, if DL *was* null, that meant we were loading directly from the alloca or global found above the test. After refactoring, this has become at least terribly subtle and potentially incorrect. There are many forms of pointer manipulation that can be traversed without DataLayout, and some of them would in fact change the size of object being loaded vs. allocated. Rather than this subtlety, I've hoisted the actual 'return true' bits into the code which actually found an alloca or global and based them on the loaded pointer being that alloca or global. This is both more clear and safer. I've also added comments about exactly why this set of predicates is used. I've also corrected a misleading comment about globals -- if overridden they may not just have a different size, they may be null and completely unsafe to load from! Hopefully this confuses the next reader a bit less. I don't have any test cases or anything, the patch is motivated strictly to improve the readability of the code. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@220156 91177308-0d34-0410-b5e6-96231b3b80d8
Analysis Opportunities:
//===---------------------------------------------------------------------===//
In test/Transforms/LoopStrengthReduce/quadradic-exit-value.ll, the
ScalarEvolution expression for %r is this:
{1,+,3,+,2}<loop>
Outside the loop, this could be evaluated simply as (%n * %n), however
ScalarEvolution currently evaluates it as
(-2 + (2 * (trunc i65 (((zext i64 (-2 + %n) to i65) * (zext i64 (-1 + %n) to i65)) /u 2) to i64)) + (3 * %n))
In addition to being much more complicated, it involves i65 arithmetic,
which is very inefficient when expanded into code.
//===---------------------------------------------------------------------===//
In formatValue in test/CodeGen/X86/lsr-delayed-fold.ll,
ScalarEvolution is forming this expression:
((trunc i64 (-1 * %arg5) to i32) + (trunc i64 %arg5 to i32) + (-1 * (trunc i64 undef to i32)))
This could be folded to
(-1 * (trunc i64 undef to i32))
//===---------------------------------------------------------------------===//