diff options
Diffstat (limited to 'gcc/tree-ssa-alias.c')
| -rw-r--r-- | gcc/tree-ssa-alias.c | 121 |
1 files changed, 115 insertions, 6 deletions
diff --git a/gcc/tree-ssa-alias.c b/gcc/tree-ssa-alias.c index 968c505..70e9e00 100644 --- a/gcc/tree-ssa-alias.c +++ b/gcc/tree-ssa-alias.c @@ -719,14 +719,113 @@ aliasing_component_refs_p (tree ref1, return false; } +/* Return true if we can determine that component references REF1 and REF2, + that are within a common DECL, cannot overlap. */ + +static bool +nonoverlapping_component_refs_of_decl_p (tree ref1, tree ref2) +{ + vec<tree, va_stack> component_refs1; + vec<tree, va_stack> component_refs2; + + vec_stack_alloc (tree, component_refs1, 16); + vec_stack_alloc (tree, component_refs2, 16); + + /* Create the stack of handled components for REF1. */ + while (handled_component_p (ref1)) + { + component_refs1.safe_push (ref1); + ref1 = TREE_OPERAND (ref1, 0); + } + if (TREE_CODE (ref1) == MEM_REF) + { + if (!integer_zerop (TREE_OPERAND (ref1, 1))) + goto may_overlap; + ref1 = TREE_OPERAND (TREE_OPERAND (ref1, 0), 0); + } + + /* Create the stack of handled components for REF2. */ + while (handled_component_p (ref2)) + { + component_refs2.safe_push (ref2); + ref2 = TREE_OPERAND (ref2, 0); + } + if (TREE_CODE (ref2) == MEM_REF) + { + if (!integer_zerop (TREE_OPERAND (ref2, 1))) + goto may_overlap; + ref2 = TREE_OPERAND (TREE_OPERAND (ref2, 0), 0); + } + + /* We must have the same base DECL. */ + gcc_assert (ref1 == ref2); + + /* Pop the stacks in parallel and examine the COMPONENT_REFs of the same + rank. This is sufficient because we start from the same DECL and you + cannot reference several fields at a time with COMPONENT_REFs (unlike + with ARRAY_RANGE_REFs for arrays) so you always need the same number + of them to access a sub-component, unless you're in a union, in which + case the return value will precisely be false. */ + while (true) + { + do + { + if (component_refs1.is_empty ()) + goto may_overlap; + ref1 = component_refs1.pop (); + } + while (!RECORD_OR_UNION_TYPE_P (TREE_TYPE (TREE_OPERAND (ref1, 0)))); + + do + { + if (component_refs2.is_empty ()) + goto may_overlap; + ref2 = component_refs2.pop (); + } + while (!RECORD_OR_UNION_TYPE_P (TREE_TYPE (TREE_OPERAND (ref2, 0)))); + + /* Beware of BIT_FIELD_REF. */ + if (TREE_CODE (ref1) != COMPONENT_REF + || TREE_CODE (ref2) != COMPONENT_REF) + goto may_overlap; + + tree field1 = TREE_OPERAND (ref1, 1); + tree field2 = TREE_OPERAND (ref2, 1); + + /* ??? We cannot simply use the type of operand #0 of the refs here + as the Fortran compiler smuggles type punning into COMPONENT_REFs + for common blocks instead of using unions like everyone else. */ + tree type1 = TYPE_MAIN_VARIANT (DECL_CONTEXT (field1)); + tree type2 = TYPE_MAIN_VARIANT (DECL_CONTEXT (field2)); + + /* We cannot disambiguate fields in a union or qualified union. */ + if (type1 != type2 || TREE_CODE (type1) != RECORD_TYPE) + goto may_overlap; + + /* Different fields of the same record type cannot overlap. */ + if (field1 != field2) + { + component_refs1.release (); + component_refs2.release (); + return true; + } + } + +may_overlap: + component_refs1.release (); + component_refs2.release (); + return false; +} + /* Return true if two memory references based on the variables BASE1 and BASE2 constrained to [OFFSET1, OFFSET1 + MAX_SIZE1) and - [OFFSET2, OFFSET2 + MAX_SIZE2) may alias. */ + [OFFSET2, OFFSET2 + MAX_SIZE2) may alias. REF1 and REF2 + if non-NULL are the complete memory reference trees. */ static bool -decl_refs_may_alias_p (tree base1, +decl_refs_may_alias_p (tree ref1, tree base1, HOST_WIDE_INT offset1, HOST_WIDE_INT max_size1, - tree base2, + tree ref2, tree base2, HOST_WIDE_INT offset2, HOST_WIDE_INT max_size2) { gcc_checking_assert (DECL_P (base1) && DECL_P (base2)); @@ -737,7 +836,17 @@ decl_refs_may_alias_p (tree base1, /* If both references are based on the same variable, they cannot alias if the accesses do not overlap. */ - return ranges_overlap_p (offset1, max_size1, offset2, max_size2); + if (!ranges_overlap_p (offset1, max_size1, offset2, max_size2)) + return false; + + /* For components with variable position, the above test isn't sufficient, + so we disambiguate component references manually. */ + if (ref1 && ref2 + && handled_component_p (ref1) && handled_component_p (ref2) + && nonoverlapping_component_refs_of_decl_p (ref1, ref2)) + return false; + + return true; } /* Return true if an indirect reference based on *PTR1 constrained @@ -1086,8 +1195,8 @@ refs_may_alias_p_1 (ao_ref *ref1, ao_ref *ref2, bool tbaa_p) var1_p = DECL_P (base1); var2_p = DECL_P (base2); if (var1_p && var2_p) - return decl_refs_may_alias_p (base1, offset1, max_size1, - base2, offset2, max_size2); + return decl_refs_may_alias_p (ref1->ref, base1, offset1, max_size1, + ref2->ref, base2, offset2, max_size2); ind1_p = (TREE_CODE (base1) == MEM_REF || TREE_CODE (base1) == TARGET_MEM_REF); |