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c-common.c (c_get_alias_set): Allow all type-punning through unions.

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        * c-common.c (c_get_alias_set): Allow all type-punning through
        unions.  Don't get confused about the type of a bit-field, despite
        the antics of build_modify_expr.

From-SVN: r23481
This commit is contained in:
Mark Mitchell 1998-10-31 13:44:46 -07:00 committed by Jeff Law
parent 43d8a6c79f
commit 08bc243195
1 changed files with 22 additions and 16 deletions
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38
gcc/c-common.c
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@ -3135,6 +3135,7 @@ c_get_alias_set (t)
tree t; tree t;
{ {
tree type; tree type;
tree u;
if (t == error_mark_node) if (t == error_mark_node)
return 0; return 0;
@ -3155,22 +3156,18 @@ c_get_alias_set (t)
the conservative assumption. */ the conservative assumption. */
return 0; return 0;
if ((TREE_CODE (t) == COMPONENT_REF /* Permit type-punning when accessing a union, provided the access
&& TREE_CODE (TREE_TYPE (TREE_OPERAND (t, 0))) == UNION_TYPE) is directly through the union. For example, this code does not
/* Also permit punning when accessing an array which is a union permit taking the address of a union member and then storing
member. This makes the current sparc va_arg macro work, but may through it. Even the type-punning allowed here is a GCC
not be otherwise necessary. */ extension, albeit a common and useful one; the C standard says
|| (TREE_CODE (t) == ARRAY_REF that such accesses have implementation-defined behavior. */
&& TREE_CODE (TREE_OPERAND (t, 0)) == COMPONENT_REF for (u = t;
&& (TREE_CODE (TREE_TYPE (TREE_OPERAND (TREE_OPERAND (t, 0), 0))) TREE_CODE (u) == COMPONENT_REF || TREE_CODE (u) == ARRAY_REF;
== UNION_TYPE))) u = TREE_OPERAND (u, 0))
/* Permit type-punning when accessing a union, provided the if (TREE_CODE (u) == COMPONENT_REF
access is directly through the union. For example, this code does && TREE_CODE (TREE_TYPE (TREE_OPERAND (u, 0))) == UNION_TYPE)
not permit taking the address of a union member and then return 0;
storing through it. Even the type-punning allowed here is a
GCC extension, albeit a common and useful one; the C standard
says that such accesses have implementation-defined behavior. */
return 0;
if (TREE_CODE (t) == INDIRECT_REF) if (TREE_CODE (t) == INDIRECT_REF)
{ {
@ -3184,6 +3181,15 @@ c_get_alias_set (t)
/* From here on, only the type matters. */ /* From here on, only the type matters. */
if (TREE_CODE (t) == COMPONENT_REF
&& DECL_BIT_FIELD_TYPE (TREE_OPERAND (t, 1)))
/* Since build_modify_expr calls get_unwidened for stores to
component references, the type of a bit field can be changed
from (say) `unsigned int : 16' to `unsigned short' or from
`enum E : 16' to `short'. We want the real type of the
bit-field in this case, not some the integral equivalent. */
type = DECL_BIT_FIELD_TYPE (TREE_OPERAND (t, 1));
if (TYPE_ALIAS_SET_KNOWN_P (type)) if (TYPE_ALIAS_SET_KNOWN_P (type))
/* If we've already calculated the value, just return it. */ /* If we've already calculated the value, just return it. */
return TYPE_ALIAS_SET (type); return TYPE_ALIAS_SET (type);