diff options
| author | Richard Biener <rguenther@suse.de> | 2020-03-11 15:34:47 +0100 |
|---|---|---|
| committer | Richard Biener <rguenther@suse.de> | 2020-03-11 15:35:51 +0100 |
| commit | cb99630f254aaec6591e0a200b79905b31d24eb3 (patch) | |
| tree | dc528f98350f3bac9c438420b4d2032bdbd7ca2d /gcc/match.pd | |
| parent | d564c5e254df744a470a658690753dc193a4fa78 (diff) | |
fold undefined pointer offsetting
This avoids breaking the old broken pointer offsetting via
(T)(ptr - ((T)0)->x) which should have used offsetof. Breakage
was exposed by the introduction of POINTER_DIFF_EXPR and making
PTA not considering that producing a pointer. The mitigation
for simple cases is to canonicalize
_2 = _1 - 8B;
o_9 = (struct obj *) _2;
to
o_9 = &MEM[_1 + -8B];
eliding one statement and the offending pointer subtraction.
2020-03-11 Richard Biener <rguenther@suse.de>
* match.pd ((T *)(ptr - ptr-cst) -> &MEM[ptr + -ptr-cst]):
New pattern.
* gcc.dg/torture/20200311-1.c: New testcase.
Diffstat (limited to 'gcc/match.pd')
| -rw-r--r-- | gcc/match.pd | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/gcc/match.pd b/gcc/match.pd index 19df0c404a4..9cb37740f1e 100644 --- a/gcc/match.pd +++ b/gcc/match.pd @@ -1864,6 +1864,15 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT) (if (ptr_difference_const (@0, @1, &diff)) { build_int_cst_type (type, diff); })))) +/* Canonicalize (T *)(ptr - ptr-cst) to &MEM[ptr + -ptr-cst]. */ +(simplify + (convert (pointer_diff @0 INTEGER_CST@1)) + (if (POINTER_TYPE_P (type)) + { build_fold_addr_expr_with_type + (build2 (MEM_REF, char_type_node, @0, + wide_int_to_tree (ptr_type_node, wi::neg (wi::to_wide (@1)))), + type); })) + /* If arg0 is derived from the address of an object or function, we may be able to fold this expression using the object or function's alignment. */ |