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dec9a2ca23
processed in the DFS out of the stack completely. Keep it exclusively in a variable. Re-shuffle some code structure to make this easier. This can have a very dramatic effect in some cases because call graphs tend to look like a high fan-out spanning tree. As a consequence, there are a large number of leaf nodes in the graph, and this technique causes leaf nodes to never even go into the stack. While this only reduces the max depth by 1, it may cause the total number of round trips through the stack to drop by a lot. Now, most of this isn't really relevant for the incremental version. =] But I wanted to prototype it first here as this variant is in ways more complex. As long as I can get the code factored well here, I'll next make the primary walk look the same. There are several refactorings this exposes I think. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207306 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))
//===---------------------------------------------------------------------===//