[ Discussed here: https://gcc.gnu.org/ml/gcc-patches/2015-04/msg01262.html ] When compiling gcc.target/x86_64/abi/callabi/vaarg-6.c, at original we have: ... ;; Function do_cpy2 (null) { char * e; char * e; e = VA_ARG_EXPR <argp>; e = VA_ARG_EXPR <argp>; if (e != b) { abort (); } } ... and after gimplify we have: ... do_cpy2 (char * argp) { char * argp.1; char * argp.2; char * b.3; char * e; argp.1 = argp; e = VA_ARG (&argp.1, 0B); argp = argp.1; argp.2 = argp; e = VA_ARG (&argp.2, 0B); argp = argp.2; b.3 = b; if (e != b.3) goto <D.1373>; else goto <D.1374>; <D.1373>: abort (); <D.1374>: } ... We'd like to generate: ... e = VA_ARG (&argp, 0B); ... instead of: ... argp.1 = argp; e = VA_ARG (&argp.1, 0B); argp = argp.1; ... The code generating the copyback 'argp = argp.1' is in gimplify_modify_expr.
Created attachment 35402 [details] patch to remove copyback
I. After removing the copyback using attached patch, and marking the va_arg first argument as addressable as suggested here ( https://gcc.gnu.org/ml/gcc-patches/2015-04/msg01314.html ) using this patch (nr 1): ... @@ -9408,6 +9458,23 @@ gimplify_va_arg_expr (tree *expr_p, gimple_seq *pre_p, } /* Transform a VA_ARG_EXPR into an VA_ARG internal function. */ + mark_addressable (valist); ap = build_fold_addr_expr_loc (loc, valist); tag = build_int_cst (build_pointer_type (type), 0); *expr_p = build_call_expr_internal_loc (loc, IFN_VA_ARG, type, 2, ap, tag); ... we get the desired: ... e = VA_ARG (&argp, 0B); e = VA_ARG (&argp, 0B); ... II. However, we subsequently run into a verify_gimple_call failure in gcc.c-torture/execute/va-arg-10.c, for the second argument of this va_copy: ... __builtin_va_copy (&apc, ap); ... D.2056 = VA_ARG (&ap, 0B); ... Presumably because ap is not marked as addressable when gimplifying the va_copy, but ap is later marked as addressable when gimplifying VA_ARG_EXPR. With this patch (nr 2), we mark the second va_copy argument as addressable when gimplifying va_copy: ... @@ -2339,6 +2340,55 @@ gimplify_call_expr (tree *expr_p, gimple_seq *pre_p, bool want_value) && DECL_BUILT_IN_CLASS (fndecl) == BUILT_IN_NORMAL) switch (DECL_FUNCTION_CODE (fndecl)) { + case BUILT_IN_VA_COPY: + mark_addressable (CALL_EXPR_ARG (*expr_p, 1)); + break; case BUILT_IN_VA_START: { builtin_va_start_p = TRUE; ... That indeed prevents the verify_gimple_call error. But the code now contains a copy: ... ap.0 = ap; __builtin_va_copy (&apc, ap.0); ... D.2057 = VA_ARG (&ap, 0B); ... The copy in itself does not look incorrect, but we'd rather not have it. III. Furthermore, patch nr 1 triggers a verify_gimple_call error on gcc.c-torture/execute/va-arg-14.c for the first argument of a va_copy: ... __builtin_va_copy (param, &local); ... D.1845 = VA_ARG (¶m, 0B); ... Using this patch (nr 3), we also mark the first argument of the copy as addressable: ... @@ -2341,6 +2341,7 @@ gimplify_call_expr (tree *expr_p, gimple_seq *pre_p, bool want_value) { case BUILT_IN_VA_COPY: mark_addressable (CALL_EXPR_ARG (*expr_p, 1)); + mark_addressable (CALL_EXPR_ARG (*expr_p, 0)); break; case BUILT_IN_VA_START: { ... That indeed prevents the verify_gimple_call failure. But it results in this code: ... param.0 = param; __builtin_va_copy (param.0, &local); ... D.1846 = VA_ARG (¶m, 0B); ... which doesn't look correct: param is unmodified by the va_copy. OTOH, the obvious tests (execute.exp=va-arg*.c, execute.exp=stdarg*.c, callabi.exp) are passing, probably because va_list is a pointer type, and va_copy modifies what param points to.
(In reply to vries from comment #2) > I. > After removing the copyback using attached patch, and marking the va_arg > first argument as addressable as suggested here ( > https://gcc.gnu.org/ml/gcc-patches/2015-04/msg01314.html ) using this patch > (nr 1): > ... > @@ -9408,6 +9458,23 @@ gimplify_va_arg_expr (tree *expr_p, gimple_seq *pre_p, > } > > /* Transform a VA_ARG_EXPR into an VA_ARG internal function. */ > + mark_addressable (valist); > ap = build_fold_addr_expr_loc (loc, valist); > tag = build_int_cst (build_pointer_type (type), 0); > *expr_p = build_call_expr_internal_loc (loc, IFN_VA_ARG, type, 2, ap, > tag); > ... > > we get the desired: > ... > e = VA_ARG (&argp, 0B); > e = VA_ARG (&argp, 0B); > ... > > > II. > However, we subsequently run into a verify_gimple_call failure in > gcc.c-torture/execute/va-arg-10.c, for the second argument of this va_copy: > ... > __builtin_va_copy (&apc, ap); > ... > D.2056 = VA_ARG (&ap, 0B); > ... > > Presumably because ap is not marked as addressable when gimplifying the > va_copy, but ap is later marked as addressable when gimplifying VA_ARG_EXPR. > > With this patch (nr 2), we mark the second va_copy argument as addressable > when gimplifying va_copy: > ... > @@ -2339,6 +2340,55 @@ gimplify_call_expr (tree *expr_p, gimple_seq *pre_p, > bool want_value) > && DECL_BUILT_IN_CLASS (fndecl) == BUILT_IN_NORMAL) > switch (DECL_FUNCTION_CODE (fndecl)) > { > + case BUILT_IN_VA_COPY: > + mark_addressable (CALL_EXPR_ARG (*expr_p, 1)); > + break; > case BUILT_IN_VA_START: > { > builtin_va_start_p = TRUE; > ... > > That indeed prevents the verify_gimple_call error. But the code now contains > a copy: > ... > ap.0 = ap; > __builtin_va_copy (&apc, ap.0); > ... > D.2057 = VA_ARG (&ap, 0B); > ... > The copy in itself does not look incorrect, but we'd rather not have it. > > > III. > Furthermore, patch nr 1 triggers a verify_gimple_call error on > gcc.c-torture/execute/va-arg-14.c for the first argument of a va_copy: > ... > __builtin_va_copy (param, &local); > ... > D.1845 = VA_ARG (¶m, 0B); > ... > > Using this patch (nr 3), we also mark the first argument of the copy as > addressable: > ... > @@ -2341,6 +2341,7 @@ gimplify_call_expr (tree *expr_p, gimple_seq *pre_p, > bool want_value) > { > case BUILT_IN_VA_COPY: > mark_addressable (CALL_EXPR_ARG (*expr_p, 1)); > + mark_addressable (CALL_EXPR_ARG (*expr_p, 0)); > break; > case BUILT_IN_VA_START: > { > ... > > That indeed prevents the verify_gimple_call failure. But it results in this > code: > ... > param.0 = param; > __builtin_va_copy (param.0, &local); > ... > D.1846 = VA_ARG (¶m, 0B); > ... > which doesn't look correct: param is unmodified by the va_copy. Well, you only get the "copy" if param is of register type (thus a pointer). So the code is correct I belive. Rather than marking the va_list arg addressable in all the cases above you should probably simply ensure the frontend marks it so from the point it creates a variable with va_list type. This is because even va_list a1, a2; a1 = a2; __builtin_va_arg (a1, ...); might go wrong when gimplifying a1 = a2. > OTOH, the obvious tests (execute.exp=va-arg*.c, execute.exp=stdarg*.c, > callabi.exp) are passing, probably because va_list is a pointer type, and > va_copy modifies what param points to.
(In reply to Richard Biener from comment #3) > (In reply to vries from comment #2) > Rather than marking the va_list arg addressable in all the cases above > you should probably simply ensure the frontend marks it so from the > point it creates a variable with va_list type. This is because even > > va_list a1, a2; > a1 = a2; > __builtin_va_arg (a1, ...); > > might go wrong when gimplifying a1 = a2. > This seems to do the trick, I'll put it through some more testing: ... diff --git a/gcc/c-family/c-common.c b/gcc/c-family/c-common.c index 9797e17..d6a93d9 10044 --- a/gcc/c-family/c-common.c +++ b/gcc/c-family/c-common.c @@ -5910,6 +5910,7 @@ set_compound_literal_name (tree decl) tree build_va_arg (location_t loc, tree expr, tree type) { + mark_addressable (expr); expr = build1 (VA_ARG_EXPR, type, expr); SET_EXPR_LOCATION (expr, loc); return expr; ...
Author: vries Date: Tue Apr 28 20:58:51 2015 New Revision: 222546 URL: https://gcc.gnu.org/viewcvs?rev=222546&root=gcc&view=rev Log: Remove ifn_va_arg ap fixup 2015-04-28 Tom de Vries <tom@codesourcery.com> PR tree-optimization/65887 * gimplify.c (gimplify_modify_expr): Remove ifn_va_arg ap fixup. * c-common.c (build_va_arg): Mark va_arg ap argument as addressable. Modified: trunk/gcc/ChangeLog trunk/gcc/c-family/ChangeLog trunk/gcc/c-family/c-common.c trunk/gcc/gimplify.c
Patch committed, marking resolved - fixed.