mirror of
https://github.com/llvm/llvm-project.git
synced 2025-05-15 08:06:08 +00:00
ca68a3ec47
a function's CFG when that CFG is unchanged. This allows transformation passes to simply claim they preserve the CFG and analysis passes to check for the CFG being preserved to remove the fanout of all analyses being listed in all passes. I've gone through and removed or cleaned up as many of the comments reminding us to do this as I could. Differential Revision: https://reviews.llvm.org/D28627 llvm-svn: 292054
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))
//===---------------------------------------------------------------------===//