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I'm about to enable the new loop predication transform by default. It has the effect of completely destroying many read only loops - which happen to be a super common idiom in our test cases. So as to preserve test coverage of other transforms, disable the new transform where it would cause sharp test coverage regressions.
(This is semantically part of the enabling commit. It's committed separate to ease revert if the actual flag flip gets reverted.)
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The reversion apparently deleted the test/Transforms directory.
Will be re-reverting again.
llvm-svn: 358552
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As it's causing some bot failures (and per request from kbarton).
This reverts commit r358543/ab70da07286e618016e78247e4a24fcb84077fda.
llvm-svn: 358546
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IndVarSimplify sometimes makes transforms basing on users that are trivially dead. In particular,
if DCE wasn't run before it, there may be a dead `sext/zext` in loop that will trigger widening
transforms, however it makes no sense to do it.
This patch teaches IndVarsSimplify ignore the mist trivial cases of that.
Differential Revision: https://reviews.llvm.org/D47974
Reviewed By: sanjoy
llvm-svn: 334567
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llvm-svn: 325215
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There is a more powerful but still simple function `isKnownViaSimpleReasoning ` that
does constant range check and few more additional checks. We use it some places (e.g.
when proving implications) and in some other places we only check constant ranges.
Currently, indvar simplifier fails to remove the check in following loop:
int inc = ...;
for (int i = inc, j = inc - 1; i < 200; ++i, ++j)
if (i > j) { ... }
This patch replaces all usages of `isKnownPredicateViaConstantRanges` with
`isKnownViaSimpleReasoning` to have smarter proofs. In particular, it fixes the
case above.
Reviewed-By: sanjoy
Differential Revision: https://reviews.llvm.org/D43175
llvm-svn: 325214
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The failures happened because of assert which was overconfident about
SCEV's proving capabilities and is generally not valid.
Differential Revision: https://reviews.llvm.org/D42835
llvm-svn: 324473
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Revert rL324453 commit which causes buildbot failures.
Differential Revision: https://reviews.llvm.org/D42835
llvm-svn: 324462
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Sometimes `isLoopEntryGuardedByCond` cannot prove predicate `a > b` directly.
But it is a common situation when `a >= b` is known from ranges and `a != b` is
known from a dominating condition. Thia patch teaches SCEV to sum these facts
together and prove strict comparison via non-strict one.
Differential Revision: https://reviews.llvm.org/D42835
llvm-svn: 324453
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Turns out we can have comparisons which are indirect users of the induction variable that we can make invariant. In this case, there is no loop invariant value contributing and we'd fail an assert.
The test case was found by a java fuzzer and reduced. It's a real cornercase. You have to have a static loop which we've already proven only executes once, but haven't broken the backedge on, and an inner phi whose result can be constant folded by SCEV using exit count reasoning but not proven by isKnownPredicate. To my knowledge, only the fuzzer has hit this case.
llvm-svn: 319583
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As noted in the nice block comment, the previous code didn't actually handle multi-entry loops correctly, it just assumed SCEV didn't analyze such loops. Given SCEV has comments to the contrary, that seems a bit suspect. More importantly, the pass actually requires loopsimplify form which ensures a loop-preheader is available. Remove the excessive generaility and shorten the code greatly.
Note that we do successfully analyze many multi-entry loops, but we do so by converting them to single entry loops. See the added test case.
llvm-svn: 316976
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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
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