diff options
Diffstat (limited to 'gcc/tree-ssa-copy.c')
| -rw-r--r-- | gcc/tree-ssa-copy.c | 57 |
1 files changed, 34 insertions, 23 deletions
diff --git a/gcc/tree-ssa-copy.c b/gcc/tree-ssa-copy.c index 7111960..28b19d9 100644 --- a/gcc/tree-ssa-copy.c +++ b/gcc/tree-ssa-copy.c @@ -188,7 +188,9 @@ merge_alias_info (tree orig, tree new) #endif /* Synchronize the type tags. If both pointers had a tag and they - are different, then something has gone wrong. */ + are different, then something has gone wrong. Type tags can + always be merged because they are flow insensitive, all the SSA + names of the same base DECL share the same type tag. */ if (new_ann->type_mem_tag == NULL_TREE) new_ann->type_mem_tag = orig_ann->type_mem_tag; else if (orig_ann->type_mem_tag == NULL_TREE) @@ -196,32 +198,41 @@ merge_alias_info (tree orig, tree new) else gcc_assert (new_ann->type_mem_tag == orig_ann->type_mem_tag); - /* Synchronize the name tags. If NEW did not have a name tag, get - it from ORIG. This happens when NEW is a compiler generated - temporary which still hasn't had its points-to information filled - in. */ - if (SSA_NAME_PTR_INFO (orig)) + /* Check that flow-sensitive information is compatible. Notice that + we may not merge flow-sensitive information here. This function + is called when propagating equivalences dictated by the IL, like + a copy operation P_i = Q_j, and from equivalences dictated by + control-flow, like if (P_i == Q_j). + + In the former case, P_i and Q_j are equivalent in every block + dominated by the assignment, so their flow-sensitive information + is always the same. However, in the latter case, the pointers + P_i and Q_j are only equivalent in one of the sub-graphs out of + the predicate, so their flow-sensitive information is not the + same in every block dominated by the predicate. + + Since we cannot distinguish one case from another in this + function, we can only make sure that if P_i and Q_j have + flow-sensitive information, they should be compatible. */ + if (SSA_NAME_PTR_INFO (orig) && SSA_NAME_PTR_INFO (new)) { struct ptr_info_def *orig_ptr_info = SSA_NAME_PTR_INFO (orig); struct ptr_info_def *new_ptr_info = SSA_NAME_PTR_INFO (new); - if (new_ptr_info == NULL) - duplicate_ssa_name_ptr_info (new, orig_ptr_info); - else if (orig_ptr_info->name_mem_tag - && new_ptr_info->name_mem_tag - && orig_ptr_info->pt_vars - && new_ptr_info->pt_vars) - { - /* Note that pointer NEW may actually have a different set - of pointed-to variables. However, since NEW is being - copy-propagated into ORIG, it must always be true that - the pointed-to set for pointer NEW is the same, or a - subset, of the pointed-to set for pointer ORIG. If this - isn't the case, we shouldn't have been able to do the - propagation of NEW into ORIG. */ - gcc_assert (bitmap_intersect_p (new_ptr_info->pt_vars, - orig_ptr_info->pt_vars)); - } + /* Note that pointer NEW and ORIG may actually have different + pointed-to variables (e.g., PR 18291 represented in + testsuite/gcc.c-torture/compile/pr18291.c). However, since + NEW is being copy-propagated into ORIG, it must always be + true that the pointed-to set for pointer NEW is the same, or + a subset, of the pointed-to set for pointer ORIG. If this + isn't the case, we shouldn't have been able to do the + propagation of NEW into ORIG. */ + if (orig_ptr_info->name_mem_tag + && new_ptr_info->name_mem_tag + && orig_ptr_info->pt_vars + && new_ptr_info->pt_vars) + gcc_assert (bitmap_intersect_p (new_ptr_info->pt_vars, + orig_ptr_info->pt_vars)); } } |