Tricky index-offset logic had been added for slices,
but not for strings. This fixes that, and also adds
tests for same behavior in string/slice cases, and adds
a new test for code in prove that had been added but not
explicitly tested.
Fixes#76270.
Change-Id: Ibd92b89e944d86b7f30b4486a9008e6f1ac6af7d
Reviewed-on: https://go-review.googlesource.com/c/go/+/723980
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The detectSliceLenRelation function incorrectly deduced lower bounds
for "len(s) - i" without checking if the subtraction could overflow
(e.g. when i is negative). This led to incorrect elimination of
bounds checks.
Fixes: #76355
Change-Id: I30ada0e5f1425929ddd8ae1b66e55096ec209b5b
Reviewed-on: https://go-review.googlesource.com/c/go/+/721920
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For v = x-y:
if y >= 0 then v <= x
if y <= x then v >= 0
(With appropriate guards against overflow/underflow.)
Fixes#76304
Change-Id: I8f8f1254156c347fa97802bd057a8379676720ae
Reviewed-on: https://go-review.googlesource.com/c/go/+/720740
Reviewed-by: Mark Freeman <markfreeman@google.com>
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Prove currently checks for 0 sign bit extraction (x>>63) at the
end of the pass, but it is more general and more useful
(and not really more work) to model right shift during
value range tracking. This handles sign bit extraction (both 0 and -1)
but also makes the value ranges available for proving bounds checks.
'go build -a -gcflags=-d=ssa/prove/debug=1 std'
finds 105 new things to prove.
https://gist.github.com/rsc/8ac41176e53ed9c2f1a664fc668e8336
For example, the compiler now recognizes that this code in
strconv does not need to check the second shift for being ≥ 64.
msb := xHi >> 63
retMantissa := xHi >> (msb + 38)
nor does this code in regexp:
return b < utf8.RuneSelf && specialBytes[b%16]&(1<<(b/16)) != 0
This code in math no longer has a bounds check on the first index:
if 0 <= n && n <= 308 {
return pow10postab32[uint(n)/32] * pow10tab[uint(n)%32]
}
The diff shows one "lost" proof in ycbcr.go but it's not really lost:
the expression was folded to a constant instead, and that only shows
up with debug=2. A diff of that output is at
https://gist.github.com/rsc/9139ed46c6019ae007f5a1ba4bb3250f
Change-Id: I84087311e0a303f00e2820d957a6f8b29ee22519
Reviewed-on: https://go-review.googlesource.com/c/go/+/716140
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If two slices start out with the same length and decrease in length by
the same amount on each round of the loop (or in the if block), then
we think their length are always equal.
For example:
if len(a) != len(b) {
return
}
for len(a) >= 4 {
a = a[4:]
b = b[4:] // proved here, omit boundary check
}
if len(a) == len(b) { // proved here
//...
}
Or, change 'for' to 'if':
if len(a) != len(b) {
return
}
if len(a) >= 4 {
a = a[4:]
b = b[4:]
}
if len(a) == len(b) { // proved here
//...
}
Fixes#75144
Change-Id: I4e5902a02b5cf8fdc122715a7dbd2fb5e9a8f5dc
Reviewed-on: https://go-review.googlesource.com/c/go/+/699155
Reviewed-by: Michael Pratt <mpratt@google.com>
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For chunked iterations (useful for, but not exclusive to,
SIMD calculations) it is common to see the combination of
```
for ; i <= len(m)-4; i += 4 {
```
and
```
r0, r1, r2, r3 := m[i], m[i+1], m[i+2], m[i+3]
``
Prove did not handle the case of len-offset1 vs index+offset2
checking, but this change fixes this. There may be other
similar cases yet to handle -- this worked for the chunked
loops for simd, as well as a handful in std.
Cherry-picked from the dev.simd branch. This CL is not
necessarily SIMD specific. Apply early to reduce risk.
Change-Id: I3785df83028d517e5e5763206653b34b2befd3d0
Reviewed-on: https://go-review.googlesource.com/c/go/+/700696
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This might have been something that prove could be educated
into figuring out, but this also works, and it also helps
prove downstream.
Adjusted the prove test, because this change moved a message.
Cherry-picked from the dev.simd branch. This CL is not
necessarily SIMD specific. Apply early to reduce risk.
Change-Id: I5eabe639eff5db9cd9766a6a8666fdb4973829cb
Reviewed-on: https://go-review.googlesource.com/c/go/+/697715
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(StringLen (StringMake _ x)) == x, just like the rules we
currently have for slices.
This helps propagate string length knowledge to places which need it.
Change-Id: Ifdcf6d1f2d430c1c4bbac32e0ea74c188eae998e
Reviewed-on: https://go-review.googlesource.com/c/go/+/682777
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I've split this into it's own CL to make git bisect more effective.
Change-Id: I436ff21a3e2362b3924de25a458534eb9947e013
Reviewed-on: https://go-review.googlesource.com/c/go/+/685821
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I've split this into it's own CL to make git bisect more effective.
Change-Id: Ib2c6dbc82fb04f50f2d17fbe6626c9fc322fb478
Reviewed-on: https://go-review.googlesource.com/c/go/+/685820
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I've split this into it's own CL to make git bisect more effective.
Change-Id: I3fbb42ec7d29169a29f7f55ef2c188317512f532
Reviewed-on: https://go-review.googlesource.com/c/go/+/685819
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I've split this into it's own CL to make git bisect more effective.
Change-Id: Iaab5f0bd2ad51e86ced8c6b8fbd371eb75eeef14
Reviewed-on: https://go-review.googlesource.com/c/go/+/685815
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I've originally used |= and &= to setup assumptions exploitable by the
operation under test but theses have multiple issues making it poor
for this usecase:
- &= does not pass the minimum value as-is, rather always set it to 0
- |= rounds up the max value to a number of the same length with all ones set
- I've never implemented them to work with negative signed numbers
Change-Id: Ie43c576fb10393e69d6f989b048823daa02b1df8
Reviewed-on: https://go-review.googlesource.com/c/go/+/656160
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If there is a phi that is computing the minimum of its two inputs,
then we know the result of the phi is smaller than or equal to both
of its inputs. Similarly for maxiumum (although max seems less useful).
This pattern happens for the case
n := copy(a, b)
n is the minimum of len(a) and len(b), so with this optimization we
know both n <= len(a) and n <= len(b). That extra information is
helpful for subsequent slicing of a or b.
Fixes#16833
Change-Id: Ib4238fd1edae0f2940f62a5516a6b363bbe7928c
Reviewed-on: https://go-review.googlesource.com/c/go/+/622240
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Change-Id: I2e4d74a86faa95321e847a061e06c3efff7f20df
Reviewed-on: https://go-review.googlesource.com/c/go/+/605775
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I was not sure this was correct so I exhaustively checked all possibilities:
https://go.dev/play/p/hjmCLm4Iagzhttps://go.dev/play/p/R9RuRGKwCbN
Change-Id: I85f053df825a4d77f978de42f8a1fcaf4b881def
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Change-Id: I419faa781db085b98ea25008ca127d0317fb34e1
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I didn't implemented negative limits since prove is most useful for BCE which
should never be negative in the first place.
Change-Id: I302ee462cdc20bd4edff0618f7e49ff66fc2a007
Reviewed-on: https://go-review.googlesource.com/c/go/+/605136
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Change-Id: Id522bde5bba627d9cdc8c3d8e907bdc168e5b13c
Reviewed-on: https://go-review.googlesource.com/c/go/+/605157
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addLocalFacts loop already ft.update which sets up limits correctly, but doing this in flowLimit help us since other values might depend on this limit.
Updates #68857
We could improve this further:
- remove mod alltogheter when we can prove a < b.
- we could do more adhoc computation in flowLimit to set umax and umin tighter
Change-Id: I5184913577b6a51a07cb53a6e6b73552a982de0b
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This help to optimize code like this:
func f(buckets *[512]bucket, v value) {
a, b := v.computeSomething()
// assume a and b are proved < 512
b := &buckets[a ^ b] // pick a random bucket
b.store(v)
}
Change-Id: I1acf702f5a8137f9ded49081b4703922879b0288
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y := bits.TrailingZeros(x)
if y > bits.Len(x.umax)-1 {
then must always be true 1 << y > x.umax which is impossible
}
Change-Id: Iab4fce1c2ef828bee3a8a4a977cbadb5f9333136
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Change-Id: Ie3c7e5eaba6a9a29389018625c4b784d07c6f173
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Move some code from when we learn that we take a branch, to when
we learn that a boolean is true or false. It is more consistent
this way (and may lead to a few more cases where we can derive
useful relations).
Change-Id: Iea7b2d6740e10c9c71c4b1546881f501da81cd21
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The constant lattice for these types is pretty simple.
We no longer need the old-style facts table, as the ordering
table now has all that information.
Change-Id: If0e118c27a4de8e9bfd727b78942185c2eb50c4b
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Handles a lot more cases where constant ranges can eliminate
various (mostly bounds failure) paths.
Fixes#66826Fixes#66692Fixes#48213
Update #57959
TODO: remove constant logic from poset code, no longer needed.
Change-Id: Id196436fcd8a0c84c7d59c04f93bd92e26a0fd7e
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This do:
- Fold always false or always true comparisons for ints and uint.
- Reduce < and <= where the true set is only one value to == with such value.
Change-Id: Ie9e3f70efd1845bef62db56543f051a50ad2532e
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Most of the test cases in the test directory use the new go:build syntax
already. Convert the rest. In general, try to place the build constraint
line below the test directive comment in more places.
For #41184.
For #60268.
Change-Id: I11c41a0642a8a26dc2eda1406da908645bbc005b
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For now, only apply the rule if either of arguments are constants. That
would catch a lot of real user code, without slowing down the compiler
with code generated for string comparison (experience in CL 410336).
Updates #57959Fixes#45928
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Currently, the prove pass can get knowledge from some specific logic
operators only before the CFG is explored, which means that the bounds
information of the branch will be ignored.
This CL updates the facts table by the logic operators in every
branch. Combined with the branch information, this will be helpful for
BCE in some circumstances.
Fixes#57243
Change-Id: I0bd164f1b47804ccfc37879abe9788740b016fd5
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Some integer comparisons with 1 and -1 can be rewritten as comparisons
with 0. For example, x < 1 is equivalent to x <= 0. This is an
advantageous transformation on riscv64 because comparisons with zero
do not require a constant to be loaded into a register. Other
architectures will likely benefit too and the transformation is
relatively benign on architectures that do not benefit.
Change-Id: I2ce9821dd7605a660eb71d76e83a61f9bae1bf25
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This reverts commit 3680b5e9c4.
Reason for revert: causes long compile times on certain functions. See issue #57959
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Fixes a performance regression due to CL 418554.
Fixes#56440
Change-Id: I6ff152e9b83084756363f49ee6b0844a7a284880
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If x+delta cannot overflow/underflow, we can derive:
x+delta < x if delta<0 (this CL included)
x+delta > x if delta>0 (this CL not included due to
a recursive stack overflow)
Remove 95 bounds checks during ./make.bat
Fixes#51622
Change-Id: I60d9bd84c5d7e81bbf808508afd09be596644f09
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We don't need this special loop construct anymore now that we do
conservative GC scanning of the top of stack. Rewrite instead to a simple
pointer increment on every iteration. This leads to having a potential
past-the-end pointer at the end of the last iteration, but that value
immediately goes dead after the loop condition fails, and the past-the-end
pointer is never live across any call.
This simplifies and speeds up loops.
R=go1.20
TODO: actually delete all support for OFORUNTIL. It is now never generated,
but code to handle it (e.g. in ssagen) is still around.
TODO: in "for _, x := range" loops, we could get rid of the index
altogether and use a "pointer to the last element" reference to determine
when the loop is complete.
Fixes#53409
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For this code:
z &= 63
_ = x<<z | x>>(64-z)
Now can prove 'x<<z' in bound. In ppc64 lowering pass, it will not
produce an extra '(ANDconst <typ.Int64> [63] z)' causing
codegen/rotate.go failed. Just remove the type check in rewrite rules
as the workaround.
Removes 32 bounds checks during make.bat.
Fixes#52563.
Change-Id: I14ed2c093ff5638dfea7de9bc7649c0f756dd71a
Reviewed-on: https://go-review.googlesource.com/c/go/+/404315
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: David Chase <drchase@google.com>
Auto-Submit: Keith Randall <khr@golang.org>
Run-TryBot: Wayne Zuo <wdvxdr@golangcn.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
