[SCEV] Canonicalize X - urem X, Y patterns

There are multiple possible ways to represent the X - urem X, Y pattern. SCEV was not canonicalizing, and thus, depending on which you analyzed, you could

[SCEV] Canonicalize X - urem X, Y patterns

There are multiple possible ways to represent the X - urem X, Y pattern. SCEV was not canonicalizing, and thus, depending on which you analyzed, you could get different results. The sub representation appears to produce strictly inferior results in practice, so I decided to canonicalize to the Y * X/Y version.

The motivation here is that runtime unroll produces the sub X - (and X, Y-1) pattern when Y is a power of two. SCEV is thus unable to recognize that an unrolled loop exits because we don't figure out that the new unrolled step evenly divides the trip count of the unrolled loop. After instcombine runs, we convert the the andn form which SCEV recognizes, so essentially, this is just fixing a nasty pass ordering dependency.

The ARM loop hardware interaction in the test diff is opague to me, but the comments in the review from others knowledge of the infrastructure appear to indicate these are improvements in loop recognition, not regressions.

Differential Revision: https://reviews.llvm.org/D114018

show more ...

[tests] Add coverage for different forms of X - urem X, Y

autogen a SCEV test file

[test][NewPM] Remove RUN lines using -analyze

Only tests in llvm/test/Analysis.

-analyze is legacy PM-specific.

This only touches files with `-passes`.

I looked through everything and made sure t

[test][NewPM] Remove RUN lines using -analyze

Only tests in llvm/test/Analysis.

-analyze is legacy PM-specific.

This only touches files with `-passes`.

I looked through everything and made sure that everything had a new PM equivalent.

Reviewed By: MaskRay

Differential Revision: https://reviews.llvm.org/D109040

show more ...

[SCEV] Fix ScalarEvolution tests under NPM

Many tests use opt's -analyze feature, which does not translate well to
NPM and has better alternatives. The alternative here is to explicitly
add a pass t

[SCEV] Fix ScalarEvolution tests under NPM

Many tests use opt's -analyze feature, which does not translate well to
NPM and has better alternatives. The alternative here is to explicitly
add a pass that calls ScalarEvolution::print().

The legacy pass manager RUNs aren't changing, but they are now pinned to
the legacy pass manager. For each legacy pass manager RUN, I added a
corresponding NPM RUN using the 'print<scalar-evolution>' pass. For
compatibility with update_analyze_test_checks.py and existing test
CHECKs, 'print<scalar-evolution>' now prints what -analyze prints per
function.

This was generated by the following Python script and failures were
manually fixed up:

import sys
for i in sys.argv:
with open(i, 'r') as f:
s = f.read()
with open(i, 'w') as f:
for l in s.splitlines():
if "RUN:" in l and ' -analyze ' in l and '\\' not in l:
f.write(l.replace(' -analyze ', ' -analyze -enable-new-pm=0 '))
f.write('\n')
f.write(l.replace(' -analyze ', ' -disable-output ').replace(' -scalar-evolution ', ' "-passes=print<scalar-evolution>" ').replace(" | ", " 2>&1 | "))
f.write('\n')
else:
f.write(l)

There are a couple failures still in ScalarEvolution under NPM, but
those are due to other unrelated naming conflicts.

Reviewed By: asbirlea

Differential Revision: https://reviews.llvm.org/D83798

show more ...

[SCEV] Add URem support to SCEV

In LLVM IR the following code:

%r = urem <ty> %t, %b

is equivalent to

%q = udiv <ty> %t, %b
%s = mul <ty> nuw %q, %b
%r = sub <ty> nuw %t, %q ; (t

[SCEV] Add URem support to SCEV

In LLVM IR the following code:

%r = urem <ty> %t, %b

is equivalent to

%q = udiv <ty> %t, %b
%s = mul <ty> nuw %q, %b
%r = sub <ty> nuw %t, %q ; (t / b) * b + (t % b) = t

As UDiv, Mul and Sub are already supported by SCEV, URem can be implemented
with minimal effort using that relation:

%r --> (-%b * (%t /u %b)) + %t

We implement two special cases:

- if %b is 1, the result is always 0
- if %b is a power-of-two, we produce a zext/trunc based expression instead

That is, the following code:

%r = urem i32 %t, 65536

Produces:

%r --> (zext i16 (trunc i32 %a to i16) to i32)

Note that while this helps get a tighter bound on the range analysis and the
known-bits analysis, this exposes some normalization shortcoming of SCEVs:

%div = udim i32 %a, 65536
%mul = mul i32 %div, 65536
%rem = urem i32 %a, 65536
%add = add i32 %mul, %rem

Will usually not be reduced.

llvm-svn: 312329

show more ...

ScalarEvolution: Add URem support

In LLVM IR the following code:

%r = urem <ty> %t, %b

is equivalent to:

%q = udiv <ty> %t, %b
%s = mul <ty> nuw %q, %b
%r = sub <ty> nuw %t, %q ;

ScalarEvolution: Add URem support

In LLVM IR the following code:

%r = urem <ty> %t, %b

is equivalent to:

%q = udiv <ty> %t, %b
%s = mul <ty> nuw %q, %b
%r = sub <ty> nuw %t, %q ; (t / b) * b + (t % b) = t

As UDiv, Mul and Sub are already supported by SCEV, URem can be
implemented with minimal effort this way.

Note: While SRem and SDiv are also related this way, SCEV does not
provides SDiv yet.

llvm-svn: 306695

show more ...