Hi,
On 4 May 2017 at 11:07, Richard Biener <rguent...@suse.de> wrote: > > The following picks the changes suggested as followup for PR80533 > that do not cause the warning regression on accessing a [0] array. > > Additionally the patch removes the unnecessary allow_compref of the > function. > > The question whether we want to allow an array to extend into > padding still stands. This patch allows it for C99 flex arrays > (but not pre-C99 GNU extension [0] due to the above warning > regression, also not for [1] or larger arrays we treat as flex arrays > when we can't see an underlying decl). > > Bootstrapped and tested on x86_64-unknown-linux-gnu, applied to trunk. > > Richard. > > 2017-05-04 Richard Biener <rguent...@suse.de> > > * tree.c (array_at_struct_end_p): Handle arrays at struct > end with flexarrays more conservatively. Refactor and treat > arrays of arrays or aggregates more strict. Fix > VIEW_CONVERT_EXPR handling. Remove allow_compref argument. > * tree.c (array_at_struct_end_p): Adjust prototype. > * emit-rtl.c (set_mem_attributes_minus_bitpos): Adjust. > * gimple-fold.c (get_range_strlen): Likewise. > * tree-chkp.c (chkp_may_narrow_to_field): Likewise. > Since this patch was committed (r247581), I've noticed regressions on arm-none-linux-gnueabihf: - PASS now FAIL [PASS => FAIL]: Executed from: gfortran.dg/dg.exp gfortran.dg/alloc_comp_auto_array_2.f90 -O3 -fomit-frame-pointer -funroll-loops -fpeel-loops -ftracer -finline-functions (test for excess errors) gfortran.dg/alloc_comp_auto_array_2.f90 -O3 -g (test for excess errors) Christophe > Index: gcc/tree.c > =================================================================== > --- gcc/tree.c (revision 247542) > +++ gcc/tree.c (working copy) > @@ -13227,18 +13235,26 @@ array_ref_up_bound (tree exp) > return NULL_TREE; > } > > -/* Returns true if REF is an array reference to an array at the end of > - a structure. If this is the case, the array may be allocated larger > - than its upper bound implies. When ALLOW_COMPREF is true considers > - REF when it's a COMPONENT_REF in addition ARRAY_REF and > - ARRAY_RANGE_REF. */ > +/* Returns true if REF is an array reference or a component reference > + to an array at the end of a structure. > + If this is the case, the array may be allocated larger > + than its upper bound implies. */ > > bool > -array_at_struct_end_p (tree ref, bool allow_compref) > +array_at_struct_end_p (tree ref) > { > - if (TREE_CODE (ref) != ARRAY_REF > - && TREE_CODE (ref) != ARRAY_RANGE_REF > - && (!allow_compref || TREE_CODE (ref) != COMPONENT_REF)) > + tree atype; > + > + if (TREE_CODE (ref) == ARRAY_REF > + || TREE_CODE (ref) == ARRAY_RANGE_REF) > + { > + atype = TREE_TYPE (TREE_OPERAND (ref, 0)); > + ref = TREE_OPERAND (ref, 0); > + } > + else if (TREE_CODE (ref) == COMPONENT_REF > + && TREE_CODE (TREE_TYPE (TREE_OPERAND (ref, 1))) == ARRAY_TYPE) > + atype = TREE_TYPE (TREE_OPERAND (ref, 1)); > + else > return false; > > while (handled_component_p (ref)) > @@ -13246,19 +13262,42 @@ array_at_struct_end_p (tree ref, bool al > /* If the reference chain contains a component reference to a > non-union type and there follows another field the reference > is not at the end of a structure. */ > - if (TREE_CODE (ref) == COMPONENT_REF > - && TREE_CODE (TREE_TYPE (TREE_OPERAND (ref, 0))) == RECORD_TYPE) > + if (TREE_CODE (ref) == COMPONENT_REF) > { > - tree nextf = DECL_CHAIN (TREE_OPERAND (ref, 1)); > - while (nextf && TREE_CODE (nextf) != FIELD_DECL) > - nextf = DECL_CHAIN (nextf); > - if (nextf) > - return false; > + if (TREE_CODE (TREE_TYPE (TREE_OPERAND (ref, 0))) == RECORD_TYPE) > + { > + tree nextf = DECL_CHAIN (TREE_OPERAND (ref, 1)); > + while (nextf && TREE_CODE (nextf) != FIELD_DECL) > + nextf = DECL_CHAIN (nextf); > + if (nextf) > + return false; > + } > } > + /* If we have a multi-dimensional array we do not consider > + a non-innermost dimension as flex array if the whole > + multi-dimensional array is at struct end. > + Same for an array of aggregates with a trailing array > + member. */ > + else if (TREE_CODE (ref) == ARRAY_REF) > + return false; > + else if (TREE_CODE (ref) == ARRAY_RANGE_REF) > + ; > + /* If we view an underlying object as sth else then what we > + gathered up to now is what we have to rely on. */ > + else if (TREE_CODE (ref) == VIEW_CONVERT_EXPR) > + break; > + else > + gcc_unreachable (); > > ref = TREE_OPERAND (ref, 0); > } > > + /* The array now is at struct end. Treat flexible arrays as > + always subject to extend, even into just padding constrained by > + an underlying decl. */ > + if (! TYPE_SIZE (atype)) > + return true; > + > tree size = NULL; > > if (TREE_CODE (ref) == MEM_REF > Index: gcc/tree.h > =================================================================== > --- gcc/tree.h (revision 247542) > +++ gcc/tree.h (working copy) > @@ -4885,12 +4885,10 @@ extern tree array_ref_up_bound (tree); > EXP, an ARRAY_REF or an ARRAY_RANGE_REF. */ > extern tree array_ref_low_bound (tree); > > -/* Returns true if REF is an array reference to an array at the end of > - a structure. If this is the case, the array may be allocated larger > - than its upper bound implies. When second argument is true considers > - REF when it's a COMPONENT_REF in addition ARRAY_REF and > - ARRAY_RANGE_REF. */ > -extern bool array_at_struct_end_p (tree, bool = false); > +/* Returns true if REF is an array reference or a component reference > + to an array at the end of a structure. If this is the case, the array > + may be allocated larger than its upper bound implies. */ > +extern bool array_at_struct_end_p (tree); > > /* Return a tree representing the offset, in bytes, of the field referenced > by EXP. This does not include any offset in DECL_FIELD_BIT_OFFSET. */ > Index: gcc/emit-rtl.c > =================================================================== > --- gcc/emit-rtl.c (revision 247542) > +++ gcc/emit-rtl.c (working copy) > @@ -1957,7 +1957,7 @@ set_mem_attributes_minus_bitpos (rtx ref > || (TREE_CODE (t2) == COMPONENT_REF > /* For trailing arrays t2 doesn't have a size that > covers all valid accesses. */ > - && ! array_at_struct_end_p (t, false))) > + && ! array_at_struct_end_p (t))) > { > attrs.expr = t2; > attrs.offset_known_p = false; > Index: gcc/gimple-fold.c > =================================================================== > --- gcc/gimple-fold.c (revision 247542) > +++ gcc/gimple-fold.c (working copy) > @@ -1235,7 +1224,7 @@ get_range_strlen (tree arg, tree length[ > the NUL. > Set *FLEXP to true if the array whose bound is being > used is at the end of a struct. */ > - if (array_at_struct_end_p (arg, true)) > + if (array_at_struct_end_p (arg)) > *flexp = true; > > arg = TREE_OPERAND (arg, 1); > Index: gcc/tree-chkp.c > =================================================================== > --- gcc/tree-chkp.c (revision 247542) > +++ gcc/tree-chkp.c (working copy) > @@ -3277,7 +3277,7 @@ chkp_may_narrow_to_field (tree ref, tree > return DECL_SIZE (field) && TREE_CODE (DECL_SIZE (field)) == INTEGER_CST > && tree_to_uhwi (DECL_SIZE (field)) != 0 > && !(flag_chkp_flexible_struct_trailing_arrays > - && array_at_struct_end_p (ref, true)) > + && array_at_struct_end_p (ref)) > && (!DECL_FIELD_OFFSET (field) > || TREE_CODE (DECL_FIELD_OFFSET (field)) == INTEGER_CST) > && (!DECL_FIELD_BIT_OFFSET (field)