Add a new pass "inductive range check elimination"

Description

Add a new pass "inductive range check elimination"

IRCE eliminates range checks of the form

0 <= A * I + B < Length

by splitting a loop's iteration space into three segments in a way
that the check is completely redundant in the middle segment. As an
example, IRCE will convert

len = < known positive >
for (i = 0; i < n; i++) {
  if (0 <= i && i < len) {
    do_something();
  } else {
    throw_out_of_bounds();
  }
}

to

len = < known positive >
limit = smin(n, len)
// no first segment
for (i = 0; i < limit; i++) {
  if (0 <= i && i < len) { // this check is fully redundant
    do_something();
  } else {
    throw_out_of_bounds();
  }
}
for (i = limit; i < n; i++) {
  if (0 <= i && i < len) {
    do_something();
  } else {
    throw_out_of_bounds();
  }
}

IRCE can deal with multiple range checks in the same loop (it takes
the intersection of the ranges that will make each of them redundant
individually).

Currently IRCE does not do any profitability analysis. That is a
TODO.

Please note that the status of this pass is *experimental*, and it is
not part of any default pass pipeline. Having said that, I will love
to get feedback and general input from people interested in trying
this out.

Differential Revision: http://reviews.llvm.org/D6693

Details

Committed
sanjoyJan 15 2015, 12:45 PM
Differential Revision
D6693: New pass: inductive range check elimination
Parents
rL226200: Revert "r226086 - Revert "r226071 - [RegisterCoalescer] Remove copies to…
Branches
Unknown
Tags
Unknown