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8161334: C2: Cast nodes hinder memory alias analysis

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Reviewed-by: kvn, thartmann
This commit is contained in:
Vladimir Ivanov 2019-02-14 15:27:46 -08:00
parent 40c61cce4b
commit d41611ebeb
1 changed files with 15 additions and 9 deletions
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24
src/hotspot/share/opto/memnode.cpp
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@ -990,7 +990,8 @@ Node* LoadNode::can_see_arraycopy_value(Node* st, PhaseGVN* phase) const {
Node* MemNode::can_see_stored_value(Node* st, PhaseTransform* phase) const {
Node* ld_adr = in(MemNode::Address);
intptr_t ld_off = 0;
AllocateNode* ld_alloc = AllocateNode::Ideal_allocation(ld_adr, phase, ld_off);
Node* ld_base = AddPNode::Ideal_base_and_offset(ld_adr, phase, ld_off);
Node* ld_alloc = AllocateNode::Ideal_allocation(ld_base, phase);
const TypeInstPtr* tp = phase->type(ld_adr)->isa_instptr();
Compile::AliasType* atp = (tp != NULL) ? phase->C->alias_type(tp) : NULL;
// This is more general than load from boxing objects.
@ -1043,16 +1044,21 @@ Node* MemNode::can_see_stored_value(Node* st, PhaseTransform* phase) const {
if (st->is_Store()) {
Node* st_adr = st->in(MemNode::Address);
if (!phase->eqv(st_adr, ld_adr)) {
// Try harder before giving up... Match raw and non-raw pointers.
// Try harder before giving up. Unify base pointers with casts (e.g., raw/non-raw pointers).
intptr_t st_off = 0;
AllocateNode* alloc = AllocateNode::Ideal_allocation(st_adr, phase, st_off);
if (alloc == NULL) return NULL;
if (alloc != ld_alloc) return NULL;
if (ld_off != st_off) return NULL;
Node* st_base = AddPNode::Ideal_base_and_offset(st_adr, phase, st_off);
if (ld_base == NULL) return NULL;
if (st_base == NULL) return NULL;
if (ld_base->uncast() != st_base->uncast()) return NULL;
if (ld_off != st_off) return NULL;
if (ld_off == Type::OffsetBot) return NULL;
// Same base, same offset.
// Possible improvement for arrays: check index value instead of absolute offset.
// At this point we have proven something like this setup:
// A = Allocate(...)
// L = LoadQ(, AddP(CastPP(, A.Parm),, #Off))
// S = StoreQ(, AddP(, A.Parm , #Off), V)
// B = << base >>
// L = LoadQ(AddP(Check/CastPP(B), #Off))
// S = StoreQ(AddP( B , #Off), V)
// (Actually, we haven't yet proven the Q's are the same.)
// In other words, we are loading from a casted version of
// the same pointer-and-offset that we stored to.