CVP currently only tries to simplify comparisons if there is a
constant operand. However, even if both are non-constant, we may
be able to determine the result of the comparison based on range
information.
IPSCCP is already capable of doing this, but because it runs very
early, it may miss some cases.
Differential Revision: https://reviews.llvm.org/D137253
This patch fixes an issue in which CorrelatedValuePropagation::processSRem
would create new instructions to represent the SRem instruction, but would not
correctly copy any existing debug location metadata to the new instruction.
Differential Revision: https://reviews.llvm.org/D132218
Clang-format InstructionSimplify and convert all "FunctionName"s to
"functionName". This patch does touch a lot of files but gets done with
the cleanup of InstructionSimplify in one commit.
This is the alternative to the less invasive clang-format only patch: D126783
Reviewed By: spatel, rengolin
Differential Revision: https://reviews.llvm.org/D126889
Most clients only used these methods because they wanted to be able to
extend or truncate to the same bit width (which is a no-op). Now that
the standard zext, sext and trunc allow this, there is no reason to use
the OrSelf versions.
The OrSelf versions additionally have the strange behaviour of allowing
extending to a *smaller* width, or truncating to a *larger* width, which
are also treated as no-ops. A small amount of client code relied on this
(ConstantRange::castOp and MicrosoftCXXNameMangler::mangleNumber) and
needed rewriting.
Differential Revision: https://reviews.llvm.org/D125557
Previously we took the old name and always appended a numberic suffix.
Since we're doing a 1:1 replacement, it's clearer to keep the original
name exactly.
Reviewed By: fhahn
Differential Revision: https://reviews.llvm.org/D125281
The "Correlated Value Propagation" pass was missing a case when handling select instructions. It was only handling the "false" constant value, while in NVPTX the select may have the condition (and thus the branches) inverted, for example:
```
loop:
%phi = phi i32* [ %sel, %loop ], [ %x, %entry ]
%f = tail call i32* @f(i32* %phi)
%cmp1 = icmp ne i32* %f, %y
%sel = select i1 %cmp1, i32* %f, i32* null
%cmp2 = icmp eq i32* %sel, null
br i1 %cmp2, label %return, label %loop
```
But the select condition can be inverted:
```
%cmp1 = icmp eq i32* %f, %y
%sel = select i1 %cmp1, i32* null, i32* %f
```
The fix is to enhance "Correlated Value Propagation" to handle both branches of the select instruction.
Reviewed By: nikic, lebedev.ri
Differential Revision: https://reviews.llvm.org/D119643
Fixes PR#52190. There is already a check for converting ashr instructions with non-negative left-hand sides into lshr; this patch adds an optimization to remove ashr altogether if the left-hand side is known to be in the range [-1, 1).
Differential Revision: https://reviews.llvm.org/D113835
This canonicalization breaks the ability to discard checks in some cases.
Add a command line option to disable it. This option is on by default,
so the change is NFC.
See for details:
https://reviews.llvm.org/D112895#3149487
Now that the reasoning was added to ConstantRange in D90924,
this replicates IndVars variant of this transform (D111836)
in a pass that uses value range reasoning for the transform.
Reviewed By: nikic
Differential Revision: https://reviews.llvm.org/D112895
This renames the primary methods for creating a zero value to `getZero`
instead of `getNullValue` and renames predicates like `isAllOnesValue`
to simply `isAllOnes`. This achieves two things:
1) This starts standardizing predicates across the LLVM codebase,
following (in this case) ConstantInt. The word "Value" doesn't
convey anything of merit, and is missing in some of the other things.
2) Calling an integer "null" doesn't make any sense. The original sin
here is mine and I've regretted it for years. This moves us to calling
it "zero" instead, which is correct!
APInt is widely used and I don't think anyone is keen to take massive source
breakage on anything so core, at least not all in one go. As such, this
doesn't actually delete any entrypoints, it "soft deprecates" them with a
comment.
Included in this patch are changes to a bunch of the codebase, but there are
more. We should normalize SelectionDAG and other APIs as well, which would
make the API change more mechanical.
Differential Revision: https://reviews.llvm.org/D109483
This reverts commit 9934a5b2ed.
This patch may cause miscompiles because it missed a constraint
as shown in the examples from:
https://llvm.org/PR51531
The common phi value transform replaces constants with values that
have the same value as the constant on a given edge. However, LVI
generally only provides information that is correct up to poison,
so this can end up replacing a well-defined value with poison.
D69442 addressed an instance of this problem by clearing poison
flags on the generating instruction, which was sufficient at the
time. rGa917fb89dc28 made LVI's edge value analysis slightly more
powerful, and clearing poison flags is no longer sufficient.
This patch changes the transform to instead explicitly guard against
a poison value instead. This should be satisfied for most cases due
to a prior branch on poison.
Fixes https://bugs.llvm.org/show_bug.cgi?id=50399.
Differential Revision: https://reviews.llvm.org/D102966
Currently all AA analyses marked as preserved are stateless, not taking
into account their dependent analyses. So there's no need to mark them
as preserved, they won't be invalidated unless their analyses are.
SCEVAAResults was the one exception to this, it was treated like a
typical analysis result. Make it like the others and don't invalidate
unless SCEV is invalidated.
Reviewed By: asbirlea
Differential Revision: https://reviews.llvm.org/D102032
Recently processMinMaxIntrinsic has been added and we started to observe a number of analysis get invalidated after CVP. The problem is CVP conservatively returns 'true' even if there were no modifications to IR. I found one more place besides processMinMaxIntrinsic which has the same problem. I think processMinMaxIntrinsic and similar should better have boolean return status to prevent similar issue reappear in future.
Reviewed By: lebedev.ri
Differential Revision: https://reviews.llvm.org/D100538
The default is likely wrong.
Out of all the callees, only a single one needs to pass-in false (JumpThread),
everything else either already passes true, or should pass true.
Until the default is flipped, at least make it harder to unintentionally
add new callees with UseBlockValue=false.
CVP currently handles switches by checking an equality predicate
on all edges from predecessor blocks. Of course, this can only
work if the value being switched over is defined in a different block.
Replace this implementation with a call to getPredicateAt(), which
also does the predecessor edge predicate check (if not defined in
the same block), but can also do quite a bit more: It can reason
about phi-nodes by checking edge predicates for incoming values,
it can reason about assumes, and it can reason about block values.
As such, this makes the implementation both simpler and more
powerful. The compile-time impact on CTMark is in the noise.
For a call site which had both constant deopt operands and nonnull arguments, we were missing the opportunity to recognize the later by bailing early.
This is somewhat of a speculative fix. Months ago, I'd had a private report of performance and compile time regressions from the deopt operand folding. I never received a test case. However, the only possibility I see was that after that change CVP missed the nonnull fold, and we end up with a pass ordering/missed simplification issue. So, since it's a real issue, fix it and hope.
Add a flag to getPredicateAt() that allows making use of the block
value. This allows us to take into account range information from
the current block, rather than only information that is threaded
over edges, making the icmp simplification in CVP a lot more
powerful.
I'm not changing getPredicateAt() to use the block value
unconditionally to avoid any impact on the JumpThreading pass,
which is somewhat picky about LVI query order.
Most test changes here are just icmps that now get dropped (while
previously only a result used in a return was replaced). The three
tests in icmp.ll show some representative improvements. Some of
the folds this enables have been covered by IPSCCP in the meantime,
but LVI can reason about some cases which are hard to support in
IPSCCP, such as in test_br_cmp_with_offset.
The compile-time time cost of doing this is fairly minimal, with
a ~0.05% CTMark regression for ReleaseThinLTO:
https://llvm-compile-time-tracker.com/compare.php?from=709d03f8af4da4204849a70f01798e7cebba2e32&to=6236fd503761f43c99f4537121e057a01056f185&stat=instructions
This is because the block values will typically already be queried
and cached by other CVP optimizations anyway.
Differential Revision: https://reviews.llvm.org/D69686
Require CxtI in getConstant() and getConstantRange() APIs.
Accordingly drop the BB parameter, as it is implied by
CxtI->getParent().
This makes sure we don't forget to pass the context instruction,
and makes the API contract clearer (also clean up the comments to
that effect -- the value holds at the context instruction, not
the end of the block).
This fold was the only place not passing the context instruction.
The tests worked around that fact by introducing a basic block split,
which is now no longer necessary.
As an exhaustive test shows, this logic is fully identical to the old
implementation, with exception of the case where both of the operands
had empty ranges:
```
TEST_F(ConstantRangeTest, CVP_UDiv) {
unsigned Bits = 4;
EnumerateConstantRanges(Bits, [&](const ConstantRange &CR0) {
if(CR0.isEmptySet())
return;
EnumerateConstantRanges(Bits, [&](const ConstantRange &CR1) {
if(CR0.isEmptySet())
return;
unsigned MaxActiveBits = 0;
for (const ConstantRange &CR : {CR0, CR1})
MaxActiveBits = std::max(MaxActiveBits, CR.getActiveBits());
ConstantRange OperandRange(Bits, /*isFullSet=*/false);
for (const ConstantRange &CR : {CR0, CR1})
OperandRange = OperandRange.unionWith(CR);
unsigned NewWidth = OperandRange.getUnsignedMax().getActiveBits();
EXPECT_EQ(MaxActiveBits, NewWidth) << CR0 << " " << CR1;
});
});
}
```
This is a continuation of 8d487668d0,
the logic is pretty much identical for SRem:
Name: pos pos
Pre: C0 >= 0 && C1 >= 0
%r = srem i8 C0, C1
=>
%r = urem i8 C0, C1
Name: pos neg
Pre: C0 >= 0 && C1 <= 0
%r = srem i8 C0, C1
=>
%r = urem i8 C0, -C1
Name: neg pos
Pre: C0 <= 0 && C1 >= 0
%r = srem i8 C0, C1
=>
%t0 = urem i8 -C0, C1
%r = sub i8 0, %t0
Name: neg neg
Pre: C0 <= 0 && C1 <= 0
%r = srem i8 C0, C1
=>
%t0 = urem i8 -C0, -C1
%r = sub i8 0, %t0
https://rise4fun.com/Alive/Vd6
Now, this new logic does not result in any new catches
as of vanilla llvm test-suite + RawSpeed.
but it should be virtually compile-time free,
and it may be important to be consistent in their handling,
because if we had a pair of sdiv-srem, and only converted one of them,
-divrempairs will no longer see them as a pair,
and thus not "merge" them.
As mentioned on D70376, LVI can currently cause performance issues
when running under NewPM. The problem is that, unlike the legacy
pass manager, NewPM will not immediately discard the LVI analysis
if the following pass does not need it. This is a problem, because
LVI has a high memory requirement, and mass invalidation of LVI
values is very inefficient. LVI should only be alive during passes
that actively interact with it.
This patch addresses the issue by explicitly abandoning LVI after CVP,
which gets us back to the LegacyPM behavior.
Differential Revision: https://reviews.llvm.org/D84959
Yes, if operands are non-positive this comes at the extra cost
of two extra negations. But a. division is already just
ridiculously costly, two more subtractions can't hurt much :)
and b. we have better/more analyzes/folds for an unsigned division,
we could end up narrowing it's bitwidth, converting it to lshr, etc.
This is essentially a take two on 0fdcca07ad,
which didn't fix the potential regression i was seeing,
because ValueTracking's computeKnownBits() doesn't make use
of dominating conditions in it's analysis.
While i could teach it that, this seems like the more general fix.
This big hammer actually does catch said potential regression.
Over vanilla test-suite + RawSpeed + darktable
(10M IR instrs, 1M IR BB, 1M X86 ASM instrs), this fires/converts 5 more
(+2%) SDiv's, the total instruction count at the end of middle-end pipeline
is only +6, so out of +10 extra negations, ~half are folded away,
and asm instr count is only +1, so practically speaking all extra
negations are folded away and are therefore free.
Sadly, all these new UDiv's remained, none folded away.
But there are two less basic blocks.
https://rise4fun.com/Alive/VS6
Name: v0
Pre: C0 >= 0 && C1 >= 0
%r = sdiv i8 C0, C1
=>
%r = udiv i8 C0, C1
Name: v1
Pre: C0 <= 0 && C1 >= 0
%r = sdiv i8 C0, C1
=>
%t0 = udiv i8 -C0, C1
%r = sub i8 0, %t0
Name: v2
Pre: C0 >= 0 && C1 <= 0
%r = sdiv i8 C0, C1
=>
%t0 = udiv i8 C0, -C1
%r = sub i8 0, %t0
Name: v3
Pre: C0 <= 0 && C1 <= 0
%r = sdiv i8 C0, C1
=>
%r = udiv i8 -C0, -C1
This patch updates ValueLattice to distinguish between ranges that are
guaranteed to not include undef and ranges that may include undef.
A constant range guaranteed to not contain undef can be used to simplify
instructions to arbitrary values. A constant range that may contain
undef can only be used to simplify to a constant. If the value can be
undef, it might take a value outside the range. For example, consider
the snipped below
define i32 @f(i32 %a, i1 %c) {
br i1 %c, label %true, label %false
true:
%a.255 = and i32 %a, 255
br label %exit
false:
br label %exit
exit:
%p = phi i32 [ %a.255, %true ], [ undef, %false ]
%f.1 = icmp eq i32 %p, 300
call void @use(i1 %f.1)
%res = and i32 %p, 255
ret i32 %res
}
In the exit block, %p would be a constant range [0, 256) including undef as
%p could be undef. We can use the range information to replace %f.1 with
false because we remove the compare, effectively forcing the use of the
constant to be != 300. We cannot replace %res with %p however, because
if %a would be undef %cond may be true but the second use might not be
< 256.
Currently LazyValueInfo uses the new behavior just when simplifying AND
instructions and does not distinguish between constant ranges with and
without undef otherwise. I think we should address the remaining issues
in LVI incrementally.
Reviewers: efriedma, reames, aqjune, jdoerfert, sstefan1
Reviewed By: efriedma
Differential Revision: https://reviews.llvm.org/D76931
CVP currently does not simplify cmps with instructions in the same
block, because LVI getPredicateAt() currently does not provide
much useful information for that case (D69686 would change that,
but is stuck.) However, if the instruction is a Phi node, then
LVI can compute the result of the predicate by threading it into
the predecessor blocks, which allows it simplify some conditions
that nothing else can handle. Relevant code:
6d6a4590c5/llvm/lib/Analysis/LazyValueInfo.cpp (L1904-L1927)
Differential Revision: https://reviews.llvm.org/D72169
Nikita Popov