| Message ID | 201109061401.55969.ebotcazou@adacore.com |
|---|---|
| State | New |
| Headers | show |
On Tue, 6 Sep 2011, Eric Botcazou wrote: > Hi, > > this is a regression present on the mainline and 4.6 branch caused by the > constructor uniquization patch. The tree_output_constant_def routine rejects > offsetof-like computations that can be written in the C family of languages. > While the C compiler folds most of them early, it doesn't if an intermediate > folding step is required. > > The proposed fix is to make c_fully_fold also do the offsetof folding. > > Tested on x86_64-suse-linux, OK for mainline and 4.6 branch? OK with a comment explaining the need to fold in this case and with the testcase moved to gcc.c-torture/compile rather than having dg-options specifying particular options from the set that would be passed in gcc.c-torture/compile. But in general we want to *reduce* the amount of folding done in the front ends and move more of it to gimplification time or later, except where required for the front end to meet standard requirements for diagnostics relating to constant expressions or avoid unnecessary warnings in various cases relating to conversions etc. (and there may be better ways to avoid those warnings without early optimization).
Index: c-common.c =================================================================== --- c-common.c (revision 178488) +++ c-common.c (working copy) @@ -1264,7 +1264,18 @@ c_fully_fold_internal (tree expr, bool i STRIP_TYPE_NOPS (op0); if (code != ADDR_EXPR && code != REALPART_EXPR && code != IMAGPART_EXPR) op0 = decl_constant_value_for_optimization (op0); - if (op0 != orig_op0 || in_init) + if (op0 != orig_op0 + && code == ADDR_EXPR + && (op1 = get_base_address (op0)) != NULL_TREE + && TREE_CODE (op1) == INDIRECT_REF + && TREE_CONSTANT (TREE_OPERAND (op1, 0))) + { + tree offset = fold_offsetof (op0, op1); + op1 + = fold_convert_loc (loc, TREE_TYPE (expr), TREE_OPERAND (op1, 0)); + ret = fold_build_pointer_plus_loc (loc, op1, offset); + } + else if (op0 != orig_op0 || in_init) ret = in_init ? fold_build1_initializer_loc (loc, code, TREE_TYPE (expr), op0) : fold_build1_loc (loc, code, TREE_TYPE (expr), op0);