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

diff --git a/gcc/go/gofrontend/MERGE b/gcc/go/gofrontend/MERGE
index 006da8c77fe8f8b57122077ae577562b7e0be8ad..4a9853ab68c783460421dcbfaba69b13649d800c 100644 (file)
--- a/gcc/go/gofrontend/MERGE
+++ b/gcc/go/gofrontend/MERGE
@@ -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.

diff --git a/gcc/go/gofrontend/expressions.cc b/gcc/go/gofrontend/expressions.cc
index f41647aa4e4c9ee5216b4007539083e4d821d1d3..018fdbbec77bd656de8997e81894d5565798052b 100644 (file)
--- a/gcc/go/gofrontend/expressions.cc
+++ b/gcc/go/gofrontend/expressions.cc
@@ -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);

diff --git a/gcc/go/gofrontend/runtime.def b/gcc/go/gofrontend/runtime.def
index 273c86040913efab8bd92cba3124912b3548e749..83a71528a8c4d5ead3bfb1f37369bab0b4bc3abd 100644 (file)
--- a/gcc/go/gofrontend/runtime.def
+++ b/gcc/go/gofrontend/runtime.def
@@ -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.

diff --git a/libgo/go/runtime/slice.go b/libgo/go/runtime/slice.go
index 335532d126b52e4be45dba95bb135e4ef67a1d77..9137951bfe9a363ce53eb85e97f871f24debca71 100644 (file)
--- a/libgo/go/runtime/slice.go
+++ b/libgo/go/runtime/slice.go
@@ -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}
 }