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At present, `-scalar-evolution-max-iterations` is a `cl::Optional` option, which means it demands to be passed exactly zero or one times. Our build system makes it pretty tricky to guarantee this. We often accidentally pass the flag more than once (but always with the same value) which results in an error, after which compilation fails: ``` clang (LLVM option parsing): for the -scalar-evolution-max-iterations option: may only occur zero or one times! ``` It seems reasonable to allow -scalar-evolution-max-iterations to be passed more than once. Quoting the [[ http://llvm.org/docs/CommandLine.html#controlling-the-number-of-occurrences-required-and-allowed | documentation ]]: > The cl::ZeroOrMore modifier ... indicates that your program will allow the option to be specified zero or more times. > ... > If an option is specified multiple times for an option of the cl::opt class, only the last value will be retained. Original patch by: Enrico Bern Hardy Tanuwidjaja <etanuwid@fb.com> Differential Revision: https://reviews.llvm.org/D67512 llvm-svn: 372346
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))
//===---------------------------------------------------------------------===//