Commit Graph

267 Commits

Author SHA1 Message Date
Wei Mi a49559befb [SCEV] Try to reuse existing value during SCEV expansion
Current SCEV expansion will expand SCEV as a sequence of operations
and doesn't utilize the value already existed. This will introduce
redundent computation which may not be cleaned up throughly by
following optimizations.

This patch introduces an ExprValueMap which is a map from SCEV to the
set of equal values with the same SCEV. When a SCEV is expanded, the
set of values is checked and reused whenever possible before generating
a sequence of operations.

The original commit triggered regressions in Polly tests. The regressions
exposed two problems which have been fixed in current version.

1. Polly will generate a new function based on the old one. To generate an
instruction for the new function, it builds SCEV for the old instruction,
applies some tranformation on the SCEV generated, then expands the transformed
SCEV and insert the expanded value into new function. Because SCEV expansion
may reuse value cached in ExprValueMap, the value in old function may be
inserted into new function, which is wrong.
   In SCEVExpander::expand, there is a logic to check the cached value to
be used should dominate the insertion point. However, for the above
case, the check always passes. That is because the insertion point is
in a new function, which is unreachable from the old function. However
for unreachable node, DominatorTreeBase::dominates thinks it will be
dominated by any other node.
   The fix is to simply add a check that the cached value to be used in
expansion should be in the same function as the insertion point instruction.

2. When the SCEV is of scConstant type, expanding it directly is cheaper than
reusing a normal value cached. Although in the cached value set in ExprValueMap,
there is a Constant type value, but it is not easy to find it out -- the cached
Value set is not sorted according to the potential cost. Existing reuse logic
in SCEVExpander::expand simply chooses the first legal element from the cached
value set.
   The fix is that when the SCEV is of scConstant type, don't try the reuse
logic. simply expand it.

Differential Revision: http://reviews.llvm.org/D12090

llvm-svn: 259736
2016-02-04 01:27:38 +00:00
Wei Mi 97de385868 Revert r259662, which caused regressions on polly tests.
llvm-svn: 259675
2016-02-03 18:05:57 +00:00
Wei Mi ed133978a0 [SCEV] Try to reuse existing value during SCEV expansion
Current SCEV expansion will expand SCEV as a sequence of operations
and doesn't utilize the value already existed. This will introduce
redundent computation which may not be cleaned up throughly by
following optimizations.

This patch introduces an ExprValueMap which is a map from SCEV to the
set of equal values with the same SCEV. When a SCEV is expanded, the
set of values is checked and reused whenever possible before generating
a sequence of operations.

Differential Revision: http://reviews.llvm.org/D12090

llvm-svn: 259662
2016-02-03 17:05:12 +00:00
Chen Li 5cde8389cf [IndVarSimplify] Rewrite loop exit values with their initial values from loop preheader
Summary:
This is a revised version of D13974, and the following quoted summary are from D13974

"This patch adds support to check if a loop has loop invariant conditions which lead to loop exits. If so, we know that if the exit path is taken, it is at the first loop iteration. If there is an induction variable used in that exit path whose value has not been updated, it will keep its initial value passing from loop preheader. We can therefore rewrite the exit value with
its initial value. This will help remove phis created by LCSSA and enable other optimizations like loop unswitch."

D13974 was committed but failed one lnt test. The bug was that we only checked the condition from loop exit's incoming block was a loop invariant. But there could be another condition from loop header to that incoming block not being a loop invariant. This would produce miscompiled code.

This patch fixes the issue by checking if the incoming block is loop header, and if not, don't perform the rewrite. The could be further improved by recursively checking all conditions leading to loop exit block, but I'd like to check in this simple version first and improve it with future patches.     

Reviewers: sanjoy

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D16570

llvm-svn: 258912
2016-01-27 07:40:41 +00:00
Sanjoy Das 29a4b5dc0d [SCEV] Fix PR26207
In some cases, the max backedge taken count can be more conservative
than the exact backedge taken count (for instance, because
ScalarEvolution::getRange is not control-flow sensitive whereas
computeExitLimitFromICmp can be).  In these cases,
computeExitLimitFromCond (specifically the bit that deals with `and` and
`or` instructions) can create an ExitLimit instance with a
`SCEVCouldNotCompute` max backedge count expression, but a computable
exact backedge count expression.  This violates an implicit SCEV
assumption: a computable exact BE count should imply a computable max BE
count.

This change

 - Makes the above implicit invariant explicit by adding an assert to
   ExitLimit's constructor

 - Changes `computeExitLimitFromCond` to be more robust around
   conservative max backedge counts

llvm-svn: 258184
2016-01-19 20:53:51 +00:00
Sanjoy Das de47590589 [IndVars] Fix PR25576
`LCSSASafePhiForRAUW` as computed was incorrect -- in cases like
these (this exact example does not actually trigger the bug):

define i32 @f(i32 %n, i1* %c) {
entry:
  br label %outer.loop

outer.loop:
  br label %inner.loop

inner.loop:
  %iv = phi i32 [ 0, %outer.loop ], [ %iv.inc, %inner.loop ]
  %iv.inc = add nuw nsw i32 %iv, 1
  %tc = udiv i32 %n, 13
  %be.cond = icmp ult i32 %iv, %tc
  br i1 %be.cond, label %inner.loop, label %inner.exit

inner.exit:
  %iv.lcssa = phi i32 [ %iv, %inner.loop ]
  %outer.be.cond = load volatile i1, i1* %c
  br i1 %outer.be.cond, label %outer.loop, label %leave

leave:
  %iv.lcssa.lcssa = phi i32 [ %iv.lcssa, %inner.exit ]
  ret i32 %iv.lcssa.lcssa
}

`LCSSASafePhiForRAUW` is true for `%iv.lcssa` when re-rewriting the exit
value of `%iv` for `%inner.loop` to `%tc` (this can happen due to
`SCEVExpander::findExistingExpansion`), but the RAUW breaks LCSSA.

To fix this, instead of computing `SafePhi` with special logic, decide
the safety of RAUW directly via `replacementPreservesLCSSAForm`.

llvm-svn: 258016
2016-01-17 18:12:52 +00:00
Sanjoy Das 683bf070ef [IndVars] Have getInsertPointForUses preserve LCSSA
Summary:
Also add a stricter post-condition for IndVarSimplify.

Fixes PR25578.  Test case by Michael Zolotukhin.

Reviewers: hfinkel, atrick, mzolotukhin

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D15059

llvm-svn: 254977
2015-12-08 00:13:21 +00:00
Sanjoy Das b771eb6d69 [SCEVExpander] Have hoistIVInc preserve LCSSA
Summary:
(Note: the problematic invocation of hoistIVInc that caused PR24804 came
from IndVarSimplify, not from SCEVExpander itself)

Fixes PR24804.  Test case by David Majnemer.

Reviewers: hfinkel, majnemer, atrick, mzolotukhin

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D15058

llvm-svn: 254976
2015-12-08 00:13:17 +00:00
Peter Collingbourne c85f4ced4d ScalarEvolution: do not set nuw when creating exprs of form <expr> + <all-ones>.
The nuw constraint will not be satisfied unless <expr> == 0.

This bug has been around since r102234 (in 2010!), but was uncovered by
r251052, which introduced more aggressive optimization of nuw scev expressions.

Differential Revision: http://reviews.llvm.org/D14850

llvm-svn: 253627
2015-11-20 01:26:13 +00:00
Sanjoy Das c1a2977fb2 Re-apply r251050 with a for PR25421
The bug: I missed adding break statements in the switch / case.

Original commit message:

[SCEV] Teach SCEV some axioms about non-wrapping arithmetic

Summary:
 - A s<  (A + C)<nsw> if C >  0
 - A s<= (A + C)<nsw> if C >= 0
 - (A + C)<nsw> s<  A if C <  0
 - (A + C)<nsw> s<= A if C <= 0

Right now `C` needs to be a constant, but we can later generalize it to
be a non-constant if needed.

Reviewers: atrick, hfinkel, reames, nlewycky

Subscribers: sanjoy, llvm-commits

Differential Revision: http://reviews.llvm.org/D13686

llvm-svn: 252236
2015-11-05 23:45:38 +00:00
Richard Trieu f8978e1a74 Revert r251050 to fix miscompile when running Clang -O1
See bug for details: https://llvm.org/bugs/show_bug.cgi?id=25421
Some comparisons were incorrectly replaced with a constant value.

llvm-svn: 252231
2015-11-05 23:20:36 +00:00
Silviu Baranga 308a7c7ed4 Fix PR25372 - teach replaceCongruentPHIs to handle cases where SE evaluates a PHI to a SCEVConstant
Summary:
Since now Scalar Evolution can create non-add rec expressions for PHI
nodes, it can also create SCEVConstant expressions. This will confuse
replaceCongruentPHIs, which previously relied on the fact that SCEV
could not produce constants in this case.

We will now replace the node with a constant in these cases - or avoid
processing the Phi in case of a type mismatch.

Reviewers: sanjoy

Subscribers: llvm-commits, majnemer

Differential Revision: http://reviews.llvm.org/D14230

llvm-svn: 251938
2015-11-03 16:27:04 +00:00
Tobias Grosser 526d52691a Revert "[IndVarSimplify] Rewrite loop exit values with their initial values from loop preheader"
Commit 251839 triggers miscompiles on some bots:

http://lab.llvm.org:8011/builders/perf-x86_64-penryn-O3-polly-fast/builds/13723

(The commit is listed in 13722, but due to an existing failure introduced in
13721 and reverted in 13723 the failure is only visible in 13723)

To verify r251839 is indeed the only change that triggered the buildbot failures
and to ensure the buildbots remain green while investigating I temporarily
revert this commit. At the current state it is unclear if this commit introduced
some miscompile or if it only exposed code to Polly that is subsequently
miscompiled by Polly.

llvm-svn: 251901
2015-11-03 07:14:39 +00:00
Chen Li d715310162 [IndVarSimplify] Rewrite loop exit values with their initial values from loop preheader
Summary:
This patch adds support to check if a loop has loop invariant conditions which lead to loop exits. If so, we know that if the exit path is taken, it is at the first loop iteration. If there is an induction variable used in that exit path whose value has not been updated, it will keep its initial value passing from loop preheader. We can therefore rewrite the exit value with
its initial value. This will help remove phis created by LCSSA and enable other optimizations like loop unswitch.


Reviewers: sanjoy

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D13974

llvm-svn: 251839
2015-11-02 22:00:15 +00:00
Sanjoy Das 337d4786e1 [SCEV] Don't create SCEV expressions that break LCSSA
Prevent `createNodeFromSelectLikePHI` from creating SCEV expressions
that break LCSSA.

A better fix for the same issue is to teach SCEVExpander to not break
LCSSA by inserting PHI nodes at appropriate places.  That's planned for
the future.

Fixes PR25360.

llvm-svn: 251756
2015-10-31 23:21:40 +00:00
Chen Li 8d23a9bbef Revert r251492 "[IndVarSimplify] Rewrite loop exit values with their
initial values from loop preheader", because it broke some bots.

llvm-svn: 251498
2015-10-28 05:15:51 +00:00
Chen Li 032a5d0cea [IndVarSimplify] Rewrite loop exit values with their initial values from loop preheader
Summary:
This patch adds support to check if a loop has loop invariant conditions which lead to loop exits. If so, we know that if the exit path is taken, it is at the first loop iteration. If there is an induction variable used in that exit path whose value has not been updated, it will keep its initial value passing from loop preheader. We can therefore rewrite the exit value with
its initial value. This will help remove phis created by LCSSA and enable other optimizations like loop unswitch.


Reviewers: sanjoy

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D13974

llvm-svn: 251492
2015-10-28 04:45:47 +00:00
Sanjoy Das 1740d72867 [SCEV] Remove a test case added in r249168
The test case wasn't testing what it was commented to be testing; and
when I tried to fix the test I noticed that SCEV does not support the
simplification that the test was supposed to test.

This change removes the test case to avoid confusion.

llvm-svn: 251053
2015-10-22 19:57:41 +00:00
Sanjoy Das 6e78b17b43 [SCEV] Opportunistically interpret unsigned constraints as signed
Summary:
An unsigned comparision is equivalent to is corresponding signed version
if both the operands being compared are positive.  Teach SCEV to use
this fact when profitable.

Reviewers: atrick, hfinkel, reames, nlewycky

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D13687

llvm-svn: 251051
2015-10-22 19:57:34 +00:00
Sanjoy Das 1123148d40 [SCEV] Teach SCEV some axioms about non-wrapping arithmetic
Summary:
 - A s<  (A + C)<nsw> if C >  0
 - A s<= (A + C)<nsw> if C >= 0
 - (A + C)<nsw> s<  A if C <  0
 - (A + C)<nsw> s<= A if C <= 0

Right now `C` needs to be a constant, but we can later generalize it to
be a non-constant if needed.

Reviewers: atrick, hfinkel, reames, nlewycky

Subscribers: sanjoy, llvm-commits

Differential Revision: http://reviews.llvm.org/D13686

llvm-svn: 251050
2015-10-22 19:57:29 +00:00
Sanjoy Das 37e87c2023 [IndVars] Have `cloneArithmeticIVUser` guess better
Summary:
`cloneArithmeticIVUser` currently trips over expression like `add %iv,
-1` when `%iv` is being zero extended -- it tries to construct the
widened use as `add %iv.zext, zext(-1)` and (correctly) fails to prove
equivalence to `zext(add %iv, -1)` (here the SCEV for `%iv` is
`{1,+,1}`).

This change teaches `IndVars` to try sign extending the non-IV operand
if that makes the newly constructed IV use equivalent to the widened
narrow IV use.

Reviewers: atrick, hfinkel, reames

Subscribers: sanjoy, llvm-commits

Differential Revision: http://reviews.llvm.org/D13717

llvm-svn: 250483
2015-10-16 01:00:47 +00:00
Sanjoy Das dd70996a5c [SCEV] Pick backedge values for phi nodes correctly
Summary:
`getConstantEvolutionLoopExitValue` and `ComputeExitCountExhaustively`
assumed all phi nodes in the loop header have the same order of incoming
values.  This is not correct, and this commit changes
`getConstantEvolutionLoopExitValue` and `ComputeExitCountExhaustively`
to lookup the backedge value of a phi node using the loop's latch block.

Unfortunately, there is still some code duplication
`getConstantEvolutionLoopExitValue` and `ComputeExitCountExhaustively`.
At some point in the future we should extract out a helper class /
method that can evolve constant evolution phi nodes across iterations.

Fixes 25060.  Thanks to Mattias Eriksson for the spot-on analysis!

Depends on D13457.

Reviewers: atrick, hfinkel

Subscribers: materi, llvm-commits

Differential Revision: http://reviews.llvm.org/D13458

llvm-svn: 249712
2015-10-08 18:28:36 +00:00
Sanjoy Das 0015e5a088 [IndVars] Preserve LCSSA in `eliminateIdentitySCEV`
Summary:
After r249211, SCEV can see through some LCSSA phis.  Add a
`replacementPreservesLCSSAForm` check before replacing uses of these phi
nodes with a simplified use of the induction variable to avoid breaking
LCSSA.

Fixes 25047.

Depends on D13460.

Reviewers: atrick, hfinkel

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D13461

llvm-svn: 249575
2015-10-07 17:38:31 +00:00
Sanjoy Das 5c8bead46d [IndVars] Don't break dominance in `eliminateIdentitySCEV`
Summary:
After r249211, `getSCEV(X) == getSCEV(Y)` does not guarantee that X and
Y are related in the dominator tree, even if X is an operand to Y (I've
included a toy example in comments, and a real example as a test case).

This commit changes `SimplifyIndVar` to require a `DominatorTree`.  I
don't think this is a problem because `ScalarEvolution` requires it
anyway.

Fixes PR25051.

Depends on D13459.

Reviewers: atrick, hfinkel

Subscribers: joker.eph, llvm-commits, sanjoy

Differential Revision: http://reviews.llvm.org/D13460

llvm-svn: 249471
2015-10-06 21:44:49 +00:00
Sanjoy Das 7d910f2b11 [SCEV] Try to prove predicates by splitting them
Summary:
This change teaches SCEV that to prove `A u< B` it is sufficient to
prove each of these facts individually:

 - B >= 0
 - A s< B
 - A >= 0

In practice, SCEV sometimes finds it easier to prove these facts
individually than to prove `A u< B` as one atomic step.

Reviewers: reames, atrick, nlewycky, hfinkel

Subscribers: sanjoy, llvm-commits

Differential Revision: http://reviews.llvm.org/D13042

llvm-svn: 249168
2015-10-02 18:50:30 +00:00
Sanjoy Das 4f1c45952c [SCEV] Don't crash on pointer comparisons
`ScalarEvolution::isImpliedCondOperandsViaNoOverflow` tries to cast the
operand type of the comparison it is given to an `IntegerType`.  This is
incorrect because it could actually be simplifying a comparison between
two pointers.  Switch it to using `getTypeSizeInBits` instead, which
does the right thing for both pointers and integers.

Fixed PR24956.

llvm-svn: 248743
2015-09-28 21:14:32 +00:00
Sanjoy Das f1090b6061 [SCEV] identical instructions don't compute equal values
Before this change `HasSameValue` would return true for distinct
`alloca` instructions if they happened to be allocating the same
type (`alloca` instructions are not specified as reading memory).  This
change adds an explicit whitelist of instruction types for which
"identical" instructions compute the same value.

Fixes PR24952.

llvm-svn: 248690
2015-09-27 21:09:48 +00:00
Sanjoy Das b174f9a316 [SCEV] Reapply 'Teach isLoopBackedgeGuardedByCond to exploit trip counts'
Summary:
If the trip count of a specific backedge is `N`, then we know that
backedge is effectively guarded by the condition `{0,+,1} u< N`.  This
change teaches SCEV to use this condition to prove things in
`isLoopBackedgeGuardedByCond`.

Depends on D12948
Depends on D12949

The original checkin, r248608 had to be backed out due to an issue with
a ObjCXX unit test.  That issue is now fixed, so re-landing.

Reviewers: atrick, reames, majnemer, hfinkel

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D12950

llvm-svn: 248638
2015-09-25 23:53:50 +00:00
Sanjoy Das 96709c4854 [SCEV] Reapply 'Exploit A < B => (A+K) < (B+K) when possible'
Summary:

This change teaches SCEV's `isImpliedCond` two new identities:

  A u< B u< -C          =>  (A + C) u< (B + C)
  A s< B s< INT_MIN - C =>  (A + C) s< (B + C)

While these are useful on their own, they're really intended to support
D12950.

The original checkin, r248606 had to be backed out due to an issue with
a ObjCXX unit test.  That issue is now fixed, so re-landing.

Reviewers: atrick, reames, majnemer, nlewycky, hfinkel

Subscribers: aadg, sanjoy, llvm-commits

Differential Revision: http://reviews.llvm.org/D12948

llvm-svn: 248637
2015-09-25 23:53:45 +00:00
Sanjoy Das 4a39b97671 Revert two SCEV changes that caused test failures in clang.
r248606: "[SCEV] Exploit A < B => (A+K) < (B+K) when possible"
r248608: "[SCEV] Teach isLoopBackedgeGuardedByCond to exploit trip counts."
llvm-svn: 248614
2015-09-25 21:16:50 +00:00
Sanjoy Das d706fa8a0c [SCEV] Teach isLoopBackedgeGuardedByCond to exploit trip counts.
Summary:
If the trip count of a specific backedge is `N`, then we know that
backedge is effectively guarded by the condition `{0,+,1} u< N`.  This
change teaches SCEV to use this condition to prove things in
`isLoopBackedgeGuardedByCond`.

Depends on D12948
Depends on D12949

Reviewers: atrick, reames, majnemer, hfinkel

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D12950

llvm-svn: 248608
2015-09-25 19:59:57 +00:00
Sanjoy Das fdec9deb13 [SCEV] Exploit A < B => (A+K) < (B+K) when possible
Summary:

This change teaches SCEV's `isImpliedCond` two new identities:

  A u< B u< -C          =>  (A + C) u< (B + C)
  A s< B s< INT_MIN - C =>  (A + C) s< (B + C)

While these are useful on their own, they're really intended to support
D12950.

Reviewers: atrick, reames, majnemer, nlewycky, hfinkel

Subscribers: aadg, sanjoy, llvm-commits

Differential Revision: http://reviews.llvm.org/D12948

llvm-svn: 248606
2015-09-25 19:59:49 +00:00
Sanjoy Das 428db150d1 [IndVars] Fix a bug in r248045.
Because -indvars widens induction variables through arithmetic,
`NeverNegative` cannot be a property of the `WidenIV` (a `WidenIV`
manages information for all transitive uses of an IV being widened,
including uses of `-1 * IV`).  Instead it must live on `NarrowIVDefUse`
which manages information for a specific def-use edge in the transitive
use list of an induction variable.

This change also adds a test case that demonstrates the problem with
r248045.

llvm-svn: 248107
2015-09-20 01:52:18 +00:00
Sanjoy Das f69d0e3384 [IndVars] Widen more comparisons for non-negative induction vars
Summary:
If an induction variable is provably non-negative, its sign extension is
equal to its zero extension.  This means narrow uses like

  icmp slt iNarrow %indvar, %rhs

can be widened into

  icmp slt iWide zext(%indvar), sext(%rhs)

Reviewers: atrick, mcrosier, hfinkel

Subscribers: hfinkel, reames, llvm-commits

Differential Revision: http://reviews.llvm.org/D12745

llvm-svn: 248045
2015-09-18 21:21:02 +00:00
Sanjoy Das 8a5526e8be [IndVars] Fix PR24783.
In `IndVarSimplify::ExpandSCEVIfNeeded`,
`SCEVExpander::findExistingExpansion` may return an `llvm::Value` that
differs in type from the SCEV it was asked to find an expansion for (but
computes the same value).  In such cases, we fall back on
`expandCodeFor`; and rely on LLVM to CSE the two equivalent
expressions (different only by a no-op cast) into a single computation.

I tried a few other approaches to fixing PR24783, all of which turned
out to be more complex than this current version:

 1. Move the `ExpandSCEVIfNeeded` logic into `expandCodeFor`.  This got
    problematic because currently we do not pass in the `Loop *` into
    `expandCodeFor`.  Changing the interface to do this is a more
    invasive change, and really does not make much semantic sense unless
    the SCEV being passed in is an add recurrence.

    There is also the problem of `expandCodeFor` being used in places
    other than `indvars` -- there may be performance / correctness
    issues elsewhere if `expandCodeFor` is moved from always generating
    IR from scratch to cache-like model.

 2. Have `findExistingExpansion` only return expression with the correct
    type.  This would make `isHighCostExpansionHelper` and thus
    `isHighCostExpansion` more conservative than necessary.

 3. Insert casts on the value returned by `findExistingExpansion` if
    needed using `InsertNoopCastOfTo`.  This is complicated because
    `InsertNoopCastOfTo` depends on internal state of its
    `SCEVExpander` (specifically `Builder.GetInserPoint()`), and this
    may not be set up when `ExpandSCEVIfNeeded` is called.

 4. Manually insert casts on the value returned by
    `findExistingExpansion` if needed using `InsertNoopCastOfTo` via
    `CastInst::Create`.  This is probably workable, but figuring out the
    location where the cast instruction needs to be inserted has enough
    edge cases (arguments, constants, invokes, LCSSA must be preserved)
    makes me feel what I have right now is simplest solution.

llvm-svn: 247749
2015-09-15 23:45:39 +00:00
Hal Finkel a8d205f145 Make ScalarEvolution::isKnownPredicate a little smarter
Here we make ScalarEvolution::isKnownPredicate, indirectly, a little smarter.
Given some relational comparison operator OP, and two AddRec SCEVs, {I,+,S} OP
{J,+,T}, we can reduce this to the comparison I OP J when S == T, both AddRecs
are for the same loop, and both are known not to wrap.

As it turns out, because of the way that backedge-guard expressions can be
leveraged when computing known predicates, this allows indvars to simplify the
if-statement comparison in this loop:

  void foo (int *a, int *b, int n) {
    for (int i = 0; i < n; ++i) {
      if (i > n)
        a[i] = b[i] + 1;
    }
  }

which, somewhat surprisingly, we were not previously optimizing away.

llvm-svn: 245400
2015-08-19 01:51:51 +00:00
Sanjoy Das 366acc175e [IndVars] Fix PR24356.
Unsigned predicates increase or decrease agnostic of the signs of their
increments.

llvm-svn: 244265
2015-08-06 20:43:41 +00:00
Sanjoy Das 6c7a186599 FileCheck'ify some wc/grep based tests; NFCI.
llvm-svn: 243378
2015-07-28 03:50:09 +00:00
Sanjoy Das 5dab205ced [IndVars] Make loop varying predicates loop invariant.
Summary:
Was D9784: "Remove loop variant range check when induction variable is
strictly increasing"

This change re-implements D9784 with the two differences:

 1. It does not use SCEVExpander and does not generate new
    instructions.  Instead, it does a quick local search for existing
    `llvm::Value`s that it needs when modifying the `icmp`
    instruction.

 2. It is more general -- it deals with both increasing and decreasing
    induction variables.

I've added all of the tests included with D9784, and two more.

As an example on what this change does (copied from D9784):

Given C code:

```
for (int i = M; i < N; i++) // i is known not to overflow
  if (i < 0) break;
  a[i] = 0;
}
```

This transformation produces:

```
for (int i = M; i < N; i++)
  if (M < 0) break;
  a[i] = 0;
}
```

Which can be unswitched into:

```
if (!(M < 0))
  for (int i = M; i < N; i++)
    a[i] = 0;
}
```

I went back and forth on whether the top level logic should live in
`SimplifyIndvar::eliminateIVComparison` or be put into its own
routine.  Right now I've put it under `eliminateIVComparison` because
even though the `icmp` is not *eliminated*, it no longer is an IV
comparison.  I'm open to putting it in its own helper routine if you
think that is better.

Reviewers: reames, nicholas, atrick

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D11278

llvm-svn: 243331
2015-07-27 21:42:49 +00:00
Sanjoy Das 6f062c8c2a [IndVars] Try to use existing values in RewriteLoopExitValues.
Summary:
In RewriteLoopExitValues, before expanding out an SCEV expression using
SCEVExpander, try to see if an existing LLVM IR expression already
computes the value we're interested in.  If so use that existing
expression.

Apart from reducing IndVars' reliance on the rest of the compilation
pipeline, this also prevents IndVars from concluding some expressions as
"high cost" when they're not.  For instance,
`InductiveRangeCheckElimination` often emits code of the following form:

```
len = umin(len_A, len_B)

loop:
  ...
  if (i++ < len)
    goto loop

outside_loop:
    use(i)
```

`SCEVExpander` refuses to rewrite the use of `i` in `outside_loop`,
since it thinks the value of `i` on loop exit, `len`, is a high cost
expansion since it contains an `umax` in it.  With this change,
`IndVars` can see that it can re-use `len` instead of creating a new
expression to compute `umin(len_A, len_B)`.

I considered putting this cleverness in `SCEVExpander`, but I was
worried that it may then have a deterimental effect on other passes
that use it.  So I decided it was better to just do this in the one
place where it seems like an obviously good idea, with the intent of
generalizing later if needed.

Reviewers: atrick, reames

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D10782

llvm-svn: 241838
2015-07-09 18:46:12 +00:00
David Majnemer 7fddeccb8b Move the personality function from LandingPadInst to Function
The personality routine currently lives in the LandingPadInst.

This isn't desirable because:
- All LandingPadInsts in the same function must have the same
  personality routine.  This means that each LandingPadInst beyond the
  first has an operand which produces no additional information.

- There is ongoing work to introduce EH IR constructs other than
  LandingPadInst.  Moving the personality routine off of any one
  particular Instruction and onto the parent function seems a lot better
  than have N different places a personality function can sneak onto an
  exceptional function.

Differential Revision: http://reviews.llvm.org/D10429

llvm-svn: 239940
2015-06-17 20:52:32 +00:00
Wei Mi e2538b5639 Enable exitValue rewrite only when the cost of expansion is low.
The patch evaluates the expansion cost of exitValue in indVarSimplify pass, and only does the rewriting when the expansion cost is low or loop can be deleted with the rewriting. It provides an option "-replexitval=" to control the default aggressiveness of the exitvalue rewriting. It also fixes some missing cases in SCEVExpander::isHighCostExpansionHelper to enhance the evaluation of SCEV expansion cost.

Differential Revision: http://reviews.llvm.org/D9800

llvm-svn: 238507
2015-05-28 21:49:07 +00:00
David Blaikie 23af64846f [opaque pointer type] Add textual IR support for explicit type parameter to the call instruction
See r230786 and r230794 for similar changes to gep and load
respectively.

Call is a bit different because it often doesn't have a single explicit
type - usually the type is deduced from the arguments, and just the
return type is explicit. In those cases there's no need to change the
IR.

When that's not the case, the IR usually contains the pointer type of
the first operand - but since typed pointers are going away, that
representation is insufficient so I'm just stripping the "pointerness"
of the explicit type away.

This does make the IR a bit weird - it /sort of/ reads like the type of
the first operand: "call void () %x(" but %x is actually of type "void
()*" and will eventually be just of type "ptr". But this seems not too
bad and I don't think it would benefit from repeating the type
("void (), void () * %x(" and then eventually "void (), ptr %x(") as has
been done with gep and load.

This also has a side benefit: since the explicit type is no longer a
pointer, there's no ambiguity between an explicit type and a function
that returns a function pointer. Previously this case needed an explicit
type (eg: a function returning a void() function was written as
"call void () () * @x(" rather than "call void () * @x(" because of the
ambiguity between a function returning a pointer to a void() function
and a function returning void).

No ambiguity means even function pointer return types can just be
written alone, without writing the whole function's type.

This leaves /only/ the varargs case where the explicit type is required.

Given the special type syntax in call instructions, the regex-fu used
for migration was a bit more involved in its own unique way (as every
one of these is) so here it is. Use it in conjunction with the apply.sh
script and associated find/xargs commands I've provided in rr230786 to
migrate your out of tree tests. Do let me know if any of this doesn't
cover your cases & we can iterate on a more general script/regexes to
help others with out of tree tests.

About 9 test cases couldn't be automatically migrated - half of those
were functions returning function pointers, where I just had to manually
delete the function argument types now that we didn't need an explicit
function type there. The other half were typedefs of function types used
in calls - just had to manually drop the * from those.

import fileinput
import sys
import re

pat = re.compile(r'((?:=|:|^|\s)call\s(?:[^@]*?))(\s*$|\s*(?:(?:\[\[[a-zA-Z0-9_]+\]\]|[@%](?:(")?[\\\?@a-zA-Z0-9_.]*?(?(3)"|)|{{.*}}))(?:\(|$)|undef|inttoptr|bitcast|null|asm).*$)')
addrspace_end = re.compile(r"addrspace\(\d+\)\s*\*$")
func_end = re.compile("(?:void.*|\)\s*)\*$")

def conv(match, line):
  if not match or re.search(addrspace_end, match.group(1)) or not re.search(func_end, match.group(1)):
    return line
  return line[:match.start()] + match.group(1)[:match.group(1).rfind('*')].rstrip() + match.group(2) + line[match.end():]

for line in sys.stdin:
  sys.stdout.write(conv(re.search(pat, line), line))

llvm-svn: 235145
2015-04-16 23:24:18 +00:00
Sanjoy Das a9f1e27a04 [SCEV] Strengthen SCEVExpander::isHighCostExpansion.
Summary:

Teach `isHighCostExpansion` to consider divisions by power-of-two
constants as cheap and add a test case.  This change is needed for a new
user of `isHighCostExpansion` that will be added in a subsequent change.

Depends on D8995.

Reviewers: atrick

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D8993

llvm-svn: 234845
2015-04-14 03:20:32 +00:00
Duncan P. N. Exon Smith 49e6a70fe3 Verifier: Call verifyModule() from llc and opt
Change `llc` and `opt` to run `verifyModule()`.  This ensures that we
check the full module before `FunctionPass::doInitialization()` ever
gets called (I was getting crashes in `DwarfDebug` instead of verifier
failures when testing a WIP patch that checks operands of compile
units).  In `opt`, also move up debug-info-stripping so that it still
runs before verification.

There was a fair bit of broken code that was sitting in tree.
Interestingly, some were cases of a `select` that referred to itself in
`-instcombine` tests (apparently an intermediate result).  I split them
off to `*-noverify.ll` tests with RUN lines like this:

    opt < %s -S -disable-verify -instcombine | opt -S | FileCheck %s

This avoids verifying the input file (so we can get the broken code into
`-instcombine), but still verifies the output with a second call to
`opt` (to verify that `-instcombine` will clean it up like it should).

llvm-svn: 233432
2015-03-27 22:04:28 +00:00
David Blaikie f72d05bc7b [opaque pointer type] Add textual IR support for explicit type parameter to gep operator
Similar to gep (r230786) and load (r230794) changes.

Similar migration script can be used to update test cases, which
successfully migrated all of LLVM and Polly, but about 4 test cases
needed manually changes in Clang.

(this script will read the contents of stdin and massage it into stdout
- wrap it in the 'apply.sh' script shown in previous commits + xargs to
apply it over a large set of test cases)

import fileinput
import sys
import re

rep = re.compile(r"(getelementptr(?:\s+inbounds)?\s*\()((<\d*\s+x\s+)?([^@]*?)(|\s*addrspace\(\d+\))\s*\*(?(3)>)\s*)(?=$|%|@|null|undef|blockaddress|getelementptr|addrspacecast|bitcast|inttoptr|zeroinitializer|<|\[\[[a-zA-Z]|\{\{)", re.MULTILINE | re.DOTALL)

def conv(match):
  line = match.group(1)
  line += match.group(4)
  line += ", "
  line += match.group(2)
  return line

line = sys.stdin.read()
off = 0
for match in re.finditer(rep, line):
  sys.stdout.write(line[off:match.start()])
  sys.stdout.write(conv(match))
  off = match.end()
sys.stdout.write(line[off:])

llvm-svn: 232184
2015-03-13 18:20:45 +00:00
Mehdi Amini 46a43556db Make DataLayout Non-Optional in the Module
Summary:
DataLayout keeps the string used for its creation.

As a side effect it is no longer needed in the Module.
This is "almost" NFC, the string is no longer
canonicalized, you can't rely on two "equals" DataLayout
having the same string returned by getStringRepresentation().

Get rid of DataLayoutPass: the DataLayout is in the Module

The DataLayout is "per-module", let's enforce this by not
duplicating it more than necessary.
One more step toward non-optionality of the DataLayout in the
module.

Make DataLayout Non-Optional in the Module

Module->getDataLayout() will never returns nullptr anymore.

Reviewers: echristo

Subscribers: resistor, llvm-commits, jholewinski

Differential Revision: http://reviews.llvm.org/D7992

From: Mehdi Amini <mehdi.amini@apple.com>
llvm-svn: 231270
2015-03-04 18:43:29 +00:00
Sanjoy Das 2d38031271 Revert some changes that were made to fix PR20680.
This re-lands change r230921.  r230921 was reverted because it broke a
clang test; a checkin fixing the clang test will be commited shortly.

Summary:
As far as I can tell, the real bug causing the issue was fixed in
r230533.  SCEVExpander should mark an increment operation as nuw or nsw
only if it can *prove* that the operation does not overflow.  There
shouldn't be any situation where we have to do something different
because of no-wrap flags generated by SCEVExpander.

Revert "IndVarSimplify: Allow LFTR to fire more often"

This reverts commit 1ade0f0faa98877b688e0b9da58e876052c1e04e (SVN: 222213).

Revert "IndVarSimplify: Don't let LFTR compare against a poison value"

This reverts commit c0f2b8b528d8a37b0a1522aae90af649d6357eb5 (SVN: 217102).

Reviewers: majnemer, atrick, spatel

Differential Revision: http://reviews.llvm.org/D7979

llvm-svn: 231018
2015-03-02 21:41:07 +00:00
NAKAMURA Takumi 0cd23c842e Revert r230921, "Revert some changes that were made to fix PR20680.", for now.
It caused a failure on clang/test/Misc/backend-optimization-failure.cpp .

llvm-svn: 230929
2015-03-02 01:14:03 +00:00
Sanjoy Das 876bd51486 Revert some changes that were made to fix PR20680.
Summary:
As far as I can tell, the real bug causing the issue was fixed in
r230533.  SCEVExpander should mark an increment operation as nuw or nsw
only if it can *prove* that the operation does not overflow.  There
shouldn't be any situation where we have to do something different
because of no-wrap flags generated by SCEVExpander.

Revert "IndVarSimplify: Allow LFTR to fire more often"

This reverts commit 1ade0f0faa98877b688e0b9da58e876052c1e04e (SVN: 222213).

Revert "IndVarSimplify: Don't let LFTR compare against a poison value"

This reverts commit c0f2b8b528d8a37b0a1522aae90af649d6357eb5 (SVN: 217102).

Reviewers: majnemer, atrick, spatel

Differential Revision: http://reviews.llvm.org/D7979

llvm-svn: 230921
2015-03-01 23:36:26 +00:00