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0bdc7cd5de
handles terminator instructions. The inline cost analysis inheritted some pretty rough handling of terminator insts from the original cost analysis, and then made it much, much worse by factoring all of the important analyses into a separate instruction visitor. That instruction visitor never visited the terminator. This works fine for things like conditional branches, but for many other things we simply computed The Wrong Value. First example are unconditional branches, which should be free but were counted as full cost. This is most significant for conditional branches where the condition simplifies and folds during inlining. We paid a 1 instruction tax on every branch in a straight line specialized path. =[ Oh, we also claimed that the unreachable instruction had cost. But it gets worse. Let's consider invoke. We never applied the call penalty. We never accounted for the cost of the arguments. Nope. Worse still, we didn't handle the *correctness* constraints of not inlining recursive invokes, or exception throwing returns_twice functions. Oops. See PR18206. Sadly, PR18206 requires yet another fix, but this refactoring is at least a huge step in that direction. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@197215 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))
//===---------------------------------------------------------------------===//