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compiler,runtime: pass old slice's ptr/len/cap by value to growslice 

In the C calling convention, on AMD64, and probably a number of
    other architectures, a 3-word struct argument is passed on stack.
    This is less efficient than passing in three registers. Further,
    this may affect the code generation in other part of the program,
    even if the function is not actually called.
    
    Slices are common in Go and append is a common slice operation,
    which calls growslice in the growing path. To improve the code
    generation, pass the slice header's three fields as separate
    values, instead of a struct, to growslice.
    
    The drawback is that this makes the runtime implementation
    slightly diverges from the gc runtime.
    
    Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/168277

From-SVN: r269811
This commit is contained in:
Ian Lance Taylor 2019-03-19 18:42:43 +00:00
parent e074803086
commit ea5ac5a69b
4 changed files with 35 additions and 24 deletions
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2
gcc/go/gofrontend/MERGE
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@ -1,4 +1,4 @@
069afe85f38c099660c5d81950d65248ed4fc516
6e5ff227d4e77d340e86bd2c5e045d5532c2d7d7
The first line of this file holds the git revision number of the last
merge done from the gofrontend repository.

24
gcc/go/gofrontend/expressions.cc
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@ -7986,23 +7986,33 @@ Builtin_call_expression::flatten_append(Gogo* gogo, Named_object* function,
// Using uint here means that if the computation of ntmp overflowed,
// we will call growslice which will panic.
Expression* left = Expression::make_temporary_reference(ntmp, loc);
left = Expression::make_cast(uint_type, left, loc);
Named_object* capfn = gogo->lookup_global("cap");
Expression* capref = Expression::make_func_reference(capfn, NULL, loc);
call_args = new Expression_list();
call_args->push_back(Expression::make_temporary_reference(s1tmp, loc));
Expression* right = Expression::make_call(capref, call_args, false, loc);
Expression* cap = Expression::make_call(capref, call_args, false, loc);
gogo->lower_expression(function, inserter, &cap);
gogo->flatten_expression(function, inserter, &cap);
Temporary_statement* c1tmp = Statement::make_temporary(int_type, cap, loc);
inserter->insert(c1tmp);
Expression* left = Expression::make_temporary_reference(ntmp, loc);
left = Expression::make_cast(uint_type, left, loc);
Expression* right = Expression::make_temporary_reference(c1tmp, loc);
right = Expression::make_cast(uint_type, right, loc);
Expression* cond = Expression::make_binary(OPERATOR_GT, left, right, loc);
Type* unsafe_ptr_type = Type::make_pointer_type(Type::make_void_type());
Expression* a1 = Expression::make_type_descriptor(element_type, loc);
Expression* a2 = Expression::make_temporary_reference(s1tmp, loc);
Expression* a3 = Expression::make_temporary_reference(ntmp, loc);
Expression* call = Runtime::make_call(Runtime::GROWSLICE, loc, 3,
a1, a2, a3);
a2 = slice_type->array_type()->get_value_pointer(gogo, a2, false);
a2 = Expression::make_cast(unsafe_ptr_type, a2, loc);
Expression* a3 = Expression::make_temporary_reference(l1tmp, loc);
Expression* a4 = Expression::make_temporary_reference(c1tmp, loc);
Expression* a5 = Expression::make_temporary_reference(ntmp, loc);
Expression* call = Runtime::make_call(Runtime::GROWSLICE, loc, 5,
a1, a2, a3, a4, a5);
call = Expression::make_unsafe_cast(slice_type, call, loc);
ref = Expression::make_temporary_reference(s1tmp, loc);

3
gcc/go/gofrontend/runtime.def
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@ -202,7 +202,8 @@ DEF_GO_RUNTIME(TYPEDSLICECOPY, "runtime.typedslicecopy",
// Grow a slice for append.
DEF_GO_RUNTIME(GROWSLICE, "runtime.growslice", P3(TYPE, SLICE, INT), R1(SLICE))
DEF_GO_RUNTIME(GROWSLICE, "runtime.growslice",
P5(TYPE, POINTER, INT, INT, INT), R1(SLICE))
// Register roots (global variables) for the garbage collector.

30
libgo/go/runtime/slice.go
View File

@ -77,31 +77,31 @@ func makeslice64(et *_type, len64, cap64 int64) unsafe.Pointer {
// and it returns a new slice with at least that capacity, with the old data
// copied into it.
// The new slice's length is set to the requested capacity.
func growslice(et *_type, old slice, cap int) slice {
func growslice(et *_type, oldarray unsafe.Pointer, oldlen, oldcap, cap int) slice {
if raceenabled {
callerpc := getcallerpc()
racereadrangepc(old.array, uintptr(old.len*int(et.size)), callerpc, funcPC(growslice))
racereadrangepc(oldarray, uintptr(oldlen*int(et.size)), callerpc, funcPC(growslice))
}
if msanenabled {
msanread(old.array, uintptr(old.len*int(et.size)))
msanread(oldarray, uintptr(oldlen*int(et.size)))
}
if cap < old.cap {
if cap < oldcap {
panic(errorString("growslice: cap out of range"))
}
if et.size == 0 {
// append should not create a slice with nil pointer but non-zero len.
// We assume that append doesn't need to preserve old.array in this case.
// We assume that append doesn't need to preserve oldarray in this case.
return slice{unsafe.Pointer(&zerobase), cap, cap}
}
newcap := old.cap
newcap := oldcap
doublecap := newcap + newcap
if cap > doublecap {
newcap = cap
} else {
if old.len < 1024 {
if oldlen < 1024 {
newcap = doublecap
} else {
// Check 0 < newcap to detect overflow
@ -125,13 +125,13 @@ func growslice(et *_type, old slice, cap int) slice {
// For powers of 2, use a variable shift.
switch {
case et.size == 1:
lenmem = uintptr(old.len)
lenmem = uintptr(oldlen)
newlenmem = uintptr(cap)
capmem = roundupsize(uintptr(newcap))
overflow = uintptr(newcap) > maxAlloc
newcap = int(capmem)
case et.size == sys.PtrSize:
lenmem = uintptr(old.len) * sys.PtrSize
lenmem = uintptr(oldlen) * sys.PtrSize
newlenmem = uintptr(cap) * sys.PtrSize
capmem = roundupsize(uintptr(newcap) * sys.PtrSize)
overflow = uintptr(newcap) > maxAlloc/sys.PtrSize
@ -144,13 +144,13 @@ func growslice(et *_type, old slice, cap int) slice {
} else {
shift = uintptr(sys.Ctz32(uint32(et.size))) & 31
}
lenmem = uintptr(old.len) << shift
lenmem = uintptr(oldlen) << shift
newlenmem = uintptr(cap) << shift
capmem = roundupsize(uintptr(newcap) << shift)
overflow = uintptr(newcap) > (maxAlloc >> shift)
newcap = int(capmem >> shift)
default:
lenmem = uintptr(old.len) * et.size
lenmem = uintptr(oldlen) * et.size
newlenmem = uintptr(cap) * et.size
capmem, overflow = math.MulUintptr(et.size, uintptr(newcap))
capmem = roundupsize(capmem)
@ -177,19 +177,19 @@ func growslice(et *_type, old slice, cap int) slice {
var p unsafe.Pointer
if et.kind&kindNoPointers != 0 {
p = mallocgc(capmem, nil, false)
// The append() that calls growslice is going to overwrite from old.len to cap (which will be the new length).
// The append() that calls growslice is going to overwrite from oldlen to cap (which will be the new length).
// Only clear the part that will not be overwritten.
memclrNoHeapPointers(add(p, newlenmem), capmem-newlenmem)
} else {
// Note: can't use rawmem (which avoids zeroing of memory), because then GC can scan uninitialized memory.
p = mallocgc(capmem, et, true)
if writeBarrier.enabled {
// Only shade the pointers in old.array since we know the destination slice p
// Only shade the pointers in oldarray since we know the destination slice p
// only contains nil pointers because it has been cleared during alloc.
bulkBarrierPreWriteSrcOnly(uintptr(p), uintptr(old.array), lenmem)
bulkBarrierPreWriteSrcOnly(uintptr(p), uintptr(oldarray), lenmem)
}
}
memmove(p, old.array, lenmem)
memmove(p, oldarray, lenmem)
return slice{p, cap, newcap}
}