Currently, the integer value in the following interface conversion gets
heap allocated:
v := 1000
fmt.Println(v)
In contrast, this conversion does not currently cause the integer value
to be heap allocated:
fmt.Println(1000)
The second example is able to avoid heap allocation because of an
optimization in walk (by Josh in #18704 and related issues) that
recognizes a literal is being used. In the first example, that
optimization is currently thwarted by the literal getting assigned
to a local variable prior to use in the interface conversion.
This CL propagates constants to interface conversions like
in the first example to avoid heap allocations, instead using
a read-only global. The net effect is roughly turning the first example
into the second.
One place this comes up in practice currently is with logging or
debug prints. For example, if we have something like:
func conditionalDebugf(format string, args ...interface{}) {
if debugEnabled {
fmt.Fprintf(io.Discard, format, args...)
}
}
Prior to this CL, this integer is heap allocated, even when the
debugEnabled flag is false, and even when the compiler
inlines conditionalDebugf:
v := 1000
conditionalDebugf("hello %d", v)
With this CL, the integer here is no longer heap allocated, even when
the debugEnabled flag is enabled, because the compiler can now see that
it can use a read-only global.
See the writeup in #71359 for more details.
CL 649076 (earlier in our stack) added most of the tests
along with debug diagnostics in convert.go to make it easier
to test this change.
Updates #71359
Updates #62653
Updates #53465
Updates #8618
Change-Id: I19a51e74b36576ebb0b9cf599267cbd2bd847ce4
Reviewed-on: https://go-review.googlesource.com/c/go/+/649079
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Using the new-ish ir.ReassignOracle is more efficient than calling
ir.StaticValue repeatedly.
This CL now uses an ir.ReassignOracle for the recent
make constant propagation introduced in CL 649035.
We also pull the main change from CL 649035 into a new function,
which we will update later in our stack. We will also use the
ReassignOracles introduced here later in our stack.
(We originally did most of this work in CL 649077, but we abandoned
that in favor of CL 649035).
We could also use an ir.ReassignOracle in the older processing of
ir.OCALLFUNC in (*escape).call, but for now, we just leave that
as a TODO.
Updates #71359
Change-Id: I6e02eeac269bde3a302622b4dfe0c8dc63ec9ffc
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When appending, if the backing store doesn't escape and a
constant-sized backing store is big enough, use a constant-sized
stack-allocated backing store instead of allocating it from the heap.
cmd/go is <0.1% bigger.
As an example of how this helps, if you edit strings/strings.go:FieldsFunc
to replace
spans := make([]span, 0, 32)
with
var spans []span
then this CL removes the first 2 allocations that are part of the growth sequence:
│ base │ exp │
│ allocs/op │ allocs/op vs base │
FieldsFunc/ASCII/16-24 3.000 ± ∞ ¹ 2.000 ± ∞ ¹ -33.33% (p=0.008 n=5)
FieldsFunc/ASCII/256-24 7.000 ± ∞ ¹ 5.000 ± ∞ ¹ -28.57% (p=0.008 n=5)
FieldsFunc/ASCII/4096-24 11.000 ± ∞ ¹ 9.000 ± ∞ ¹ -18.18% (p=0.008 n=5)
FieldsFunc/ASCII/65536-24 18.00 ± ∞ ¹ 16.00 ± ∞ ¹ -11.11% (p=0.008 n=5)
FieldsFunc/ASCII/1048576-24 30.00 ± ∞ ¹ 28.00 ± ∞ ¹ -6.67% (p=0.008 n=5)
FieldsFunc/Mixed/16-24 2.000 ± ∞ ¹ 2.000 ± ∞ ¹ ~ (p=1.000 n=5)
FieldsFunc/Mixed/256-24 7.000 ± ∞ ¹ 5.000 ± ∞ ¹ -28.57% (p=0.008 n=5)
FieldsFunc/Mixed/4096-24 11.000 ± ∞ ¹ 9.000 ± ∞ ¹ -18.18% (p=0.008 n=5)
FieldsFunc/Mixed/65536-24 18.00 ± ∞ ¹ 16.00 ± ∞ ¹ -11.11% (p=0.008 n=5)
FieldsFunc/Mixed/1048576-24 30.00 ± ∞ ¹ 28.00 ± ∞ ¹ -6.67% (p=0.008 n=5)
(Of course, people have spotted and fixed a bunch of allocation sites
like this, but now we're ~automatically doing it everywhere going forward.)
No significant increases in frame sizes in cmd/go.
Change-Id: I301c4d9676667eacdae0058960321041d173751a
Reviewed-on: https://go-review.googlesource.com/c/go/+/664299
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(I noticed the one mistake in hashtriemap.go and figured I'd clean up
others.)
Change-Id: I4ade424b400056f161bc6c9c2838ba1f96b1f6bb
Reviewed-on: https://go-review.googlesource.com/c/go/+/615675
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Since CL 522318, all closures are now hidden. Thus this CL removes all
codes that worries about hidden vs non-hidden closures.
Change-Id: I1ea124168c76cedbfc4053d2f150937a382aa330
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Field.Sym now always contains the original symbol as it appeared in Go
source, so we don't need OrigSym anymore.
Instead, when the mangled name is desired, Field.Nname.Sym() can be
used instead, which is always non-nil if Nname is non-nil.
Change-Id: I96cd61db6458d4a2e07ec5810239236e3dfba747
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The types.RecvsParamsResults, etc. helpers existed to make it "easier"
to iterate over all parameters, or recvs+params, or params+results;
but they end up still being quite clumsy to use due to the design goal
of not allocating temporary slices.
Now that recvs+params+results are stored in a single consecutive slice
anyway, we can just return different subslices and simplify the loops.
Change-Id: I84791b80dc099dfbfbbe6eddbc006135528c23b4
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This CL removes a lot of the redundant methods for accessing struct
fields and signature parameters. In particular, users never have to
write ".Slice()" or ".FieldSlice()" anymore; the exported APIs just do
what you want.
Further internal refactorings to follow.
Change-Id: I45212f6772fe16aad39d0e68b82d71b0796e5639
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An *ir.Func is always ODCLFUNC, so no need to double-check this
anymore. The type system statically ensures we have the right Op.
Also, pkginit.initRequiredForCoverage appears to be unused, so we can
get rid of it completely.
Change-Id: If1abb35672b40f705f23c365ad2a828c2661e9c0
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This CL implements the remainder of the zero-copy string->[]byte
conversion optimization initially attempted in go.dev/cl/520395, but
fixes the tracking of mutations due to ODEREF/ODOTPTR assignments, and
adds more comprehensive tests that I should have included originally.
However, this CL also keeps it behind the -d=zerocopy flag. The next
CL will enable it by default (for easier rollback).
Updates #2205.
Change-Id: Ic330260099ead27fc00e2680a59c6ff23cb63c2b
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This reverts CL 520395.
Reason for revert: thanm@ pointed out failure cases.
Change-Id: I3fd60b73118be3652be2c08b77ab39e793b42110
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This CL enables the latent support for string->[]byte conversions
added go.dev/cl/520259.
One catch is that we need to make sure []byte("") evaluates to a
non-nil slice, even if "" is (nil, 0). This CL addresses that by
adding a "ptr != nil" check for OSTR2BYTESTMP, unless the NonNil flag
is set.
The existing uses of OSTR2BYTESTMP (which aren't concerned about
[]byte("") evaluating to nil) are updated to set this flag.
Fixes#2205.
Change-Id: I35a9cb16c164cd86156b7560915aba5108d8b523
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This CL extends escape analysis in two ways.
First, we already optimize directly called closures. For example,
given:
var x int // already stack allocated today
p := func() *int { return &x }()
we don't need to move x to the heap, because we can statically track
where &x flows. This CL extends the same idea to work for indirectly
called closures too, as long as we know everywhere that they're
called. For example:
var x int // stack allocated after this CL
f := func() *int { return &x }
p := f()
This will allow a subsequent CL to move the generation of go/defer
wrappers earlier.
Second, this CL adds tracking to detect when pointer values flow to
the pointee operand of an indirect assignment statement (i.e., flows
to p in "*p = x") or to builtins that modify memory (append, copy,
clear). This isn't utilized in the current CL, but a subsequent CL
will make use of it to better optimize string->[]byte conversions.
Updates #2205.
Change-Id: I610f9c531e135129c947684833e288ce64406f35
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This CL introduces a locAttr bitset type, which will make it easier to
add additional attributes in the near future.
Change-Id: I2689aa623097279dc1e7b7cf2adf5184d710c5a8
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I want to add more location properties (e.g., to track indirect stores
and calls), and it's easier to reason about them if they're all
consistent that "true" means more consequences than less.
Change-Id: I3f8674bb11877ba33082a0f5f7d8e55ad6d7a4cc
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Discarded values never persist, so they can be transiently allocated
too.
Change-Id: I036ce0c1eea45e437142497bb7df3ecb44b56e52
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Decls used to contain initializer statement for package-level
variables, but now it only contains ir.Funcs. So we might as well
rename it to Funcs and tighten its type to []*ir.Func.
Similarly, Externs always contains *ir.Names, so its type can be
constrained too.
Change-Id: I85b833e2f83d9d3559ab0ef8ab5d8324f4bc37b6
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Pass type checker error codes to base.ErrorfAt function calls
in the compiler (but don't do anything yet with the code).
Also, provide error codes to base.ErrorfAt calls in the
compiler as needed.
This opens the door towards reporting the error code and/or
providing a link/reference to more detailed explanations
(see internal/types/errors/codes.go).
Change-Id: I0ff9368d8163499ffdac6adfe8331fdc4a19b4b3
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This CL exports the existing ir.UintptrKeepAlive via the new directive
//go:uintptrkeepalive. This makes the compiler insert KeepAlives for
pointers converted to uintptr in calls, keeping them alive for the
duration of the call.
//go:uintptrkeepalive requires //go:nosplit, as stack growth can't
handle these arguments (it cannot know which are pointers). We currently
check this on the immediate function, but the actual restriction applies
to all transitive calls.
The existing //go:uintptrescapes is an extension of
//go:uintptrkeepalive which forces pointers to escape to the heap, thus
eliminating the stack growth issue.
This pragma is limited to the standard library.
For #51087
Change-Id: If9a19d484d3561b4219e5539b70c11a3cc09391e
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Fixes#52278
Change-Id: Ibf67c7b019feec277d316e04d93b458efea133fb
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This reverts commit e550c30545.
Reason for revert: Method bound calls are no longer implemented using interface calls, so it is no longer necessary. Leaving the test, though.
Change-Id: I80f1e4cd921063cd27ca8f07998316ca282e075b
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The problem in 51355 is that escape analysis decided that the
dictionary variable was captured by reference instead of by value. We
want dictionaries to always be captured by value.
Escape analysis was confused because it saw what it thought was a
reassignment of the dictionary variable. In fact, it was the only
assignment, it just wasn't marked as the defining assignment. Fix
that.
Add an assert to make sure this stays true.
Fixes#51355
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Let T be a type parameter, and say we instantiate it with S, a type
that isn't pointer-like (e.g. a pair of ints, or as in 50182, a
slice). Then to call a method m on a variable of type T, the compiler
does essentially:
var v T = ...
i := (interface{m()})(v)
i.m()
The conversion at that second line allocates, as we need to make the
data word for an interface. And in the general case, that interface
may live an arbitrarily long time. But in this case, we know it
doesn't.
The data word of i has type *S. When we call i.m, we can't call S.m
directly. It is expecting an S, not a *S. We call through a wrapper
defined on *S, which looks like:
func (p *S) m() {
var s S = *p
s.m()
}
The value passed in for p is exactly the data word mentioned above. It
never escapes anywhere - the wrapper copies a type S variable out of
*p and p is dead after that. That means that in the situation where we
build an interface for the explicit purpose of calling a method on it,
and use that built interface nowhere else, the allocation of the data
word for that interface is known to die before the call returns and
thus can be stack allocated.
One tricky case is that although the allocation of the backing store
of the interface conversion doesn't escape, pointers we store *inside*
that allocation might escape (in fact they definitely will, unless we
can devirtualize the receiver).
Fixes#50182
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This CL formalizes the closure-var trick used for method-value
wrappers to be reusable for defining other functions that take hidden
parameters via the closure-context register. In particular, it:
1. Adds a new ir.NewHiddenParam function for creating hidden
parameters.
2. Changes ir.NewClosureVar to copy Type/Typecheck from the closure
variable, so that callers can needing to manually copy these.
3. Updates existing code accordingly (i.e., method-value wrappers to
start using ir.NewHiddenParam, and closure builders to stop copying
types).
Longer term, I anticipate using this to pass dictionaries to stenciled
functions within unified IR.
Change-Id: I9da3ffdb2a26d15c6e89a21b4e080686d6dc872c
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Go spec call them "method values", not "partial calls". Note that
we use "OMETHVALUE" (as opposed to "OMETHODVALUE") to be consistent
with "OMETHEXPR".
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This CL changes escape analysis to skip reporting diagnostics (at
least for parameter tagging) for generated wrappers.
We're inconsistent about when/where wrappers are generated, which made
errorcheck tests of escape analysis unnecessarily brittle to changes
in wrapper generation. This CL addresses this making errorcheck tests
only care about tagging of the actual functions themselves, not the
wrappers too.
Change-Id: Ia1a0b9dabee4d4162b05647f871db03b032c945a
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This CL moves two bits of related code from order.go to escape
analysis:
1. The recognition of "unsafe uintptr" arguments passed to
syscall-like functions.
2. The wrapping of go/defer function calls in parameter-free function
literals.
As with previous CLs, it would be nice to push this logic even further
forward, but for now escape analysis seems most pragmatic.
A couple side benefits:
1. It allows getting rid of the uintptrEscapesHack kludge.
2. When inserting wrappers, we can move some expressions into the
wrapper and escape analyze them better. For example, the test
expectation changes are all due to slice literals in go/defer calls
where the slice is now constructed at the call site, and can now be
stack allocated.
Change-Id: I73679bcad7fa8d61d2fc52d4cea0dc5ff0de8c0c
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This CL reorganizes the code from package escape into multiple files,
so the relationships between bits of code are hopefully easier to
follow. Besides moving code around and adding necessary
copyright/import declarations, no code is touched at all.
Change-Id: Iddd396c3a140f4eb1a7a6266d92a4098118b575b
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This CL removes the special escape analysis tags added to support
//go:uintptrescapes and calls to external functions. Instead, these
are kept as function pragmas.
This CL by itself isn't very interesting, but I expect will help with
subsequent cleanups I have planned here.
Change-Id: Ifb960289a27e0a6295ce2d2f5ec233cac590522b
Reviewed-on: https://go-review.googlesource.com/c/go/+/329969
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This CL implements a few improvements to SSA devirtualization to make
it simpler and more general:
1. Change reflectdata.ITabAddr to now immediately generate the wrapper
functions and write out the itab symbol data. Previously, these were
each handled by separate phases later on.
2. Removes the hack in typecheck where we marked itabs that we
expected to need later. Instead, the calls to ITabAddr in walk now
handle generating the wrappers.
3. Changes the SSA interface call devirtualization algorithm to just
use the itab symbol data (namely, its relocations) to figure out what
pointer is available in memory at the given offset. This decouples it
somewhat from reflectdata.
Change-Id: I8fe06922af8f8a1e7c93f5aff2b60ff59b8e7114
Reviewed-on: https://go-review.googlesource.com/c/go/+/327871
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When converting a variable of generic type to an interface, use the
entry in the dictionary for the type field instead of using the
compile-time type (which we only have when fully stenciling).
Note: this isn't all the conversions. Conversions often get processed
in the ir.OCALL case. Those aren't handled yet.
Change-Id: I9a6a4c572e3c54a8e8efad98365184dbb94c4487
Reviewed-on: https://go-review.googlesource.com/c/go/+/325330
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Ensure that formal parameter Names are correctly copied and marked
with the correct Curfn. We need to ensure this even when the underlying
closure has no type parameters.
(Aside: it is strange that the types of things contain formal
parameter names that need to be copied. Maybe that's an underlying
larger problem that needs to be fixed.)
Fixes#45738
Change-Id: Ia13d69eea992ff7080bd44065115bc52eb624e73
Reviewed-on: https://go-review.googlesource.com/c/go/+/313652
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Include type information on exported function bodies, so that the
importer does not have to re-typecheck the body. This involves
including type information in the encoded output, as well as
avoiding some of the opcode rewriting and other changes that the
old exporter did assuming there would be a re-typechecking pass.
This CL could be considered a cleanup, but is more important than that
because it is an enabling change for generics. Without this CL, we'd
have to upgrade the current typechecker to understand generics. With
this CL, the current typechecker can mostly go away in favor of the
types2 typechecker.
For now, inlining of functions that contain closures is turned off.
We will hopefully resolve this before freeze.
Object files are only 0.07% bigger.
Change-Id: I85c9da09f66bfdc910dc3e26abb2613a1831634d
Reviewed-on: https://go-review.googlesource.com/c/go/+/301291
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Reviewed-by: Dan Scales <danscales@google.com>
One of escape analysis's responsibilities is to summarize whether/how
each function parameter flows to the heap so we can correctly
incorporate those flows into callers' escape analysis data flow
graphs.
As an optimization, we separately record when parameters flow to
result parameters, so that we can more precisely analyze parameter
flows based on how the results are used at the call site. However, if
a named result parameter itself needs to be heap allocated, this
optimization isn't safe and the parameter needs to be recorded as
flowing to heap rather than flowing to result.
Escape analysis used to get this correct because it conservatively
rewalked the data-flow graph multiple times. So even though it would
incorrectly record the result parameter flow, it would separately find
a flow to the heap. However, CL 196811 (specifically, case 3)
optimized the walking logic to reduce unnecessary rewalks causing us
to stop finding the extra heap flow.
This CL fixes the issue by correcting location.leakTo to be sensitive
to sink.escapes and not record result-flows when the result parameter
escapes to the heap.
Fixes#44614.
Change-Id: I48742ed35a6cab591094e2d23a439e205bd65c50
Reviewed-on: https://go-review.googlesource.com/c/go/+/297289
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In reflect.methodWrapper, we call escape analysis without including the
full batch of dependent functions, including the closure functions.
Because of this, we haven't created locations for the params/local
variables of a closure when we are processing a function that
inlines that closure. (Whereas in the normal compilation of the
function, we do call with the full batch.) To deal with this, I am
creating locations for the params/local variables of a closure when
needed.
Without this fix, the new test closure6.go would fail.
Updates #43818
Change-Id: I5f91cfb6f35efe2937ef88cbcc468e403e0da9ad
Reviewed-on: https://go-review.googlesource.com/c/go/+/285677
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I have exporting, importing, and inlining of functions with closures
working in all cases (issue #28727). all.bash runs successfully without
errors.
Approach:
- Write out the Func type, Dcls, ClosureVars, and Body when exporting
an OCLOSURE.
- When importing an OCLOSURE, read in the type, dcls, closure vars,
and body, and then do roughly equivalent code to (*noder).funcLit
- During inlining of a closure within inlined function, create new
nodes for all params and local variables (including closure
variables), so they can have a new Curfn and some other field
values. Must substitute not only on the Nbody of the closure, but
also the Type, Cvars, and Dcl fields.
Fixes#28727
Change-Id: I4da1e2567c3fa31a5121afbe82dc4e5ee32b3170
Reviewed-on: https://go-review.googlesource.com/c/go/+/283112
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This CL splits out ORETJMP as a new TailCallStmt node, separate from
the other BranchStmt nodes. In doing so, this allows us to change it
from identifying a function by *types.Sym to identifying one by
directly pointing to the *ir.Func.
While here, also rename the operation to OTAILCALL.
Passes toolstash -cmp.
Change-Id: I273e6ea5d92bf3005ae02fb59b3240a190a6cf1b
Reviewed-on: https://go-review.googlesource.com/c/go/+/284227
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It is always used with global variables, so we can skip analyze it, the
same as what we are doing for ONAME/PEXTERN nodes.
While at it, add a Fatalf check to ensure NewNameOffsetExpr is only
called for global variables.
For #43737
Change-Id: Iac444ed8d583baba5042bea096531301843b1e8f
Reviewed-on: https://go-review.googlesource.com/c/go/+/284118
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Went in a semi-automated way through the clearest renames of functions,
and updated comments and error messages where it made sense.
Change-Id: Ied8e152b562b705da7f52f715991a77dab60da35
Reviewed-on: https://go-review.googlesource.com/c/go/+/284216
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This CL moves almost all PAUTOHEAP handling code to SSA construction.
Instead of changing Names to PAUTOHEAP, escape analysis now only sets
n.Esc() to ir.EscHeap, and SSA handles creating the "&x"
pseudo-variables and associating them via Heapaddr.
This CL also gets rid of n.Stackcopy, which was used to distinguish
the heap copy of a parameter used within a function from the stack
copy used in the function calling convention. In practice, this is
always obvious from context: liveness and function prologue/epilogue
want to know about the stack copies, and everywhere else wants the
heap copy.
Hopefully moving all parameter/result handling into SSA helps with
making the register ABI stuff easier.
Also, the only remaining uses of PAUTOHEAP are now for closure
variables, so I intend to rename it to PCLOSUREVAR or get rid of those
altogether too. But this CL is already big and scary enough.
Change-Id: Ief5ef6205041b9d0ee445314310c0c5a98187e77
Reviewed-on: https://go-review.googlesource.com/c/go/+/283233
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Escape analysis needs to know the index of result parameters for
recording escape-flow information. It currently relies on Vargen for
this, but it can easily figure this out for itself. So just do that
instead, so that we can remove Vargen.
Passes toolstash -cmp.
For #43633.
Change-Id: I65dedc2d73bc25e85ff400f308e50b73dc503630
Reviewed-on: https://go-review.googlesource.com/c/go/+/283192
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After the previous CLs, all closure reads are handled during SSA
construction.
Change-Id: Iad67b01fa2d3798f50ea647be7ccf8195f189c27
Reviewed-on: https://go-review.googlesource.com/c/go/+/281512
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Similar to with regular closures, we can change method value wrappers
to use ClosureVars and allow SSA construction to take care of wiring
it up appropriately.
Change-Id: I05c0b1bcec4e24305324755df35b7bc5b8a6ce7a
Reviewed-on: https://go-review.googlesource.com/c/go/+/281353
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Now that CaptureVars is gone, we can remove the extra code in escape
analysis that only served to appease toolstash -cmp.
Change-Id: I8c811834f3d966e76702e2d362e3de414c94bea6
Reviewed-on: https://go-review.googlesource.com/c/go/+/281544
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Capture analysis is now part of escape analysis.
Passes toolstash -cmp.
Change-Id: Ifcd3ecc342074c590e0db1ff0646dfa1ea2ff57b
Reviewed-on: https://go-review.googlesource.com/c/go/+/281543
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Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Currently we rely on the type-checker to do some basic data-flow
analysis to help decide whether function literals should capture
variables by value or reference. However, this analysis isn't done by
go/types, and escape analysis already has a better framework for doing
this more precisely.
This CL extends escape analysis to recalculate the same "byval" as
CaptureVars and check that it matches. A future CL will remove
CaptureVars in favor of escape analysis's calculation.
Notably, escape analysis happens after deadcode removes obviously
unreachable code, so it sees the AST without any unreachable
assignments. (Also without unreachable addrtakens, but
ComputeAddrtaken already happens after deadcode too.) There are two
test cases where a variable is only reassigned on certain CPUs. This
CL changes them to reassign the variables unconditionally (as no-op
reassignments that avoid triggering cmd/vet's self-assignment check),
at least until we remove CaptureVars.
Passes toolstash -cmp.
Change-Id: I7162619739fedaf861b478fb8d506f96a6ac21f3
Reviewed-on: https://go-review.googlesource.com/c/go/+/281535
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There's a bunch of code that wants to map closure variables back to
their original name, so add a single Name.Canonical method that they
can all use.
Also, move the Byval flag from being stored on individual closure
variables to being stored on the canonical variable.
Passes toolstash -cmp.
Change-Id: Ia3ef81af5a15783d09f04b4e274ce33df94518e6
Reviewed-on: https://go-review.googlesource.com/c/go/+/281541
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thepudds
Keith Randall
Brad Fitzpatrick
Cuong Manh Le
Matthew Dempsky
Robert Griesemer
Michael Pratt
nimelehin
Josh Bleecher Snyder
Dan Scales