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
This formulation might be slightly slower since I eagerly compute the cheap replacements. If anyone sees this having a compile time impact, let me know and I'll use lazy population instead.
llvm-svn: 317048
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
Previously, the code returned early from the *function* when it couldn't find a free expansion, it should be returning from the *transform*. I don't have a test case, noticed this via inspection.
As a follow up, I'm going to revisit the logic in the extract function. I think that essentially the whole helper routine can be replaced with SCEVExpander, but I wanted to do that in a series of separate commits.
llvm-svn: 316974
Issue found by llvm-isel-fuzzer on OSS fuzz, https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=3725
If anyone actually cares about > 64 bit arithmetic, there's a lot more to do in this area. There's a bunch of obviously wrong code in the same function. I don't have the time to fix all of them and am just using this to understand what the workflow for fixing fuzzer cases might look like.
llvm-svn: 316967
The type of a SCEVConstant may not match the corresponding LLVM Value.
In this case, we skip the constant folding for now.
TODO: Replace ConstantInt Zero by ConstantPointerNull
llvm-svn: 314531
This patch tries to transform cases like:
for (unsigned i = 0; i < N; i += 2) {
bool c0 = (i & 0x1) == 0;
bool c1 = ((i + 1) & 0x1) == 1;
}
To
for (unsigned i = 0; i < N; i += 2) {
bool c0 = true;
bool c1 = true;
}
This commit also update test/Transforms/IndVarSimplify/replace-srem-by-urem.ll to prevent constant folding.
Differential Revision: https://reviews.llvm.org/D38272
llvm-svn: 314266
Since now SCEV can handle 'urem', an 'urem' is a better canonical form than an 'srem' because it has well-defined behavior
This is a follow up of D34598
Differential Revision: https://reviews.llvm.org/D38072
llvm-svn: 314125
The patch was reverted due to a bug. The bug was that if the IV is the 2nd operand of the icmp
instruction, then the "Pred" variable gets swapped and differs from the instruction's predicate.
In this patch we use the original predicate to do the transformation.
Also added a test case that exercises this situation.
Differentian Revision: https://reviews.llvm.org/D35107
llvm-svn: 307477
It seems that the patch was reverted by mistake. Clang testing showed failure of the
MathExtras.SaturatingMultiply test, however I was unable to reproduce the issue on the
fresh code base and was able to confirm that the transformation introduced by the change
does not happen in the said test. This gives a strong confidence that the actual reason of
the failure of the initial patch was somewhere else, and that problem now seems to be
fixed. Re-submitting the change to confirm that.
llvm-svn: 307244
This adds exact flags to AShr/LShr flags where we can statically
prove it is valid using the range of induction variables. This
allows further optimisations to remove extra loads.
Differential Revision: https://reviews.llvm.org/D34207
llvm-svn: 307157
This patch seems to cause failures of test MathExtras.SaturatingMultiply on
multiple buildbots. Reverting until the reason of that is clarified.
Differential Revision: https://reviews.llvm.org/rL307126
llvm-svn: 307135
-If there is a IndVar which is known to be non-negative, and there is a value which is also non-negative,
then signed and unsigned comparisons between them produce the same result. Both of those can be
seen in the same loop. To allow other optimizations to simplify them, we turn all instructions like
%c = icmp slt i32 %iv, %b
to
%c = icmp ult i32 %iv, %b
if both %iv and %b are known to be non-negative.
Differential Revision: https://reviews.llvm.org/D34979
llvm-svn: 307126
In rL300494 there was an attempt to deal with excessive compile time on
invocations of getSign/ZeroExtExpr using local caching. This approach only
helps if we request the same SCEV multiple times throughout recursion. But
in the bug PR33431 we see a case where we request different values all the time,
so caching does not help and the size of the cache grows enormously.
In this patch we remove the local cache for this methods and add the recursion
depth limit instead, as we do for arithmetics. This gives us a guarantee that the
invocation sequence is limited and reasonably short.
Differential Revision: https://reviews.llvm.org/D34273
llvm-svn: 306785
This is a fix for PR33292 that shows a case of extremely long compilation
of a single .c file with clang, with most time spent within SCEV.
We have a mechanism of limiting recursion depth for getAddExpr to avoid
long analysis in SCEV. However, there are calls from getAddExpr to getMulExpr
and back that do not propagate the info about depth. As result of this, a chain
getAddExpr -> ... .> getAddExpr -> getMulExpr -> getAddExpr -> ... -> getAddExpr
can be extremely long, with every segment of getAddExpr's being up to max depth long.
This leads either to long compilation or crash by stack overflow. We face this situation while
analyzing big SCEVs in the test of PR33292.
This patch applies the same limit on max expression depth for getAddExpr and getMulExpr.
Differential Revision: https://reviews.llvm.org/D33984
llvm-svn: 305463
Michael Zolotukhin
Philip Reames
Hongbin Zheng
Max Kazantsev
David Green
Sanjoy Das