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author | Patrick Palka <ppalka@redhat.com> | 2020-04-02 16:03:18 -0400 |
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committer | Patrick Palka <ppalka@redhat.com> | 2020-04-04 12:15:15 -0400 |
commit | 49a86fce1a879a206fb4b27f097910005d968fda (patch) | |
tree | 12bed14c9db0a934c281b3c82703588d322faf56 /gcc/cp/constexpr.c | |
parent | 37244b217a7329792f4ec48027f63cf5010b0ea8 (diff) | |
download | gcc-49a86fce1a879a206fb4b27f097910005d968fda.zip gcc-49a86fce1a879a206fb4b27f097910005d968fda.tar.gz gcc-49a86fce1a879a206fb4b27f097910005d968fda.tar.bz2 |
c++: Refrain from using replace_placeholders in constexpr evaluation [PR94205]
This removes the use of replace_placeholders in cxx_eval_constant_expression
(which is causing the new test lambda-this6.C to ICE due to replace_placeholders
mutating the shared TARGET_EXPR_INITIAL tree which then trips up the
gimplifier).
In its place, this patch adds a 'parent' field to constexpr_ctx which is used to
store a pointer to an outer constexpr_ctx that refers to another object under
construction. With this new field, we can beef up lookup_placeholder to resolve
PLACEHOLDER_EXPRs which refer to former objects under construction, which fixes
PR94205 without needing to do replace_placeholders. Also we can now respect the
CONSTRUCTOR_PLACEHOLDER_BOUNDARY flag when resolving PLACEHOLDER_EXPRs, and
doing so fixes the constexpr analogue of PR79937.
gcc/cp/ChangeLog:
PR c++/94205
PR c++/79937
* constexpr.c (struct constexpr_ctx): New field 'parent'.
(cxx_eval_bare_aggregate): Propagate CONSTRUCTOR_PLACEHOLDER_BOUNDARY
flag from the original constructor to the reduced constructor.
(lookup_placeholder): Prefer to return the outermost matching object
by recursively calling lookup_placeholder on the 'parent' context,
but don't cross CONSTRUCTOR_PLACEHOLDER_BOUNDARY constructors.
(cxx_eval_constant_expression): Link the 'ctx' context to the 'new_ctx'
context via 'new_ctx.parent' when being expanded without an explicit
target. Don't call replace_placeholders.
(cxx_eval_outermost_constant_expr): Initialize 'ctx.parent' to NULL.
gcc/testsuite/ChangeLog:
PR c++/94205
PR c++/79937
* g++.dg/cpp1y/pr79937-5.C: New test.
* g++.dg/cpp1z/lambda-this6.C: New test.
Diffstat (limited to 'gcc/cp/constexpr.c')
-rw-r--r-- | gcc/cp/constexpr.c | 25 |
1 files changed, 17 insertions, 8 deletions
diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c index 8fa1f53..96497ab 100644 --- a/gcc/cp/constexpr.c +++ b/gcc/cp/constexpr.c @@ -1076,6 +1076,9 @@ struct constexpr_ctx { tree object; /* If inside SWITCH_EXPR. */ constexpr_switch_state *css_state; + /* The aggregate initialization context inside which this one is nested. This + is used by lookup_placeholder to resolve PLACEHOLDER_EXPRs. */ + const constexpr_ctx *parent; /* Whether we should error on a non-constant expression or fail quietly. This flag needs to be here, but some of the others could move to global @@ -3841,6 +3844,9 @@ cxx_eval_bare_aggregate (const constexpr_ctx *ctx, tree t, vec<constructor_elt, va_gc> **p = &CONSTRUCTOR_ELTS (ctx->ctor); vec_alloc (*p, vec_safe_length (v)); + if (CONSTRUCTOR_PLACEHOLDER_BOUNDARY (t)) + CONSTRUCTOR_PLACEHOLDER_BOUNDARY (ctx->ctor) = 1; + unsigned i; tree index, value; bool constant_p = true; @@ -5303,6 +5309,12 @@ lookup_placeholder (const constexpr_ctx *ctx, bool lval, tree type) if (!ctx) return NULL_TREE; + /* Prefer the outermost matching object, but don't cross + CONSTRUCTOR_PLACEHOLDER_BOUNDARY constructors. */ + if (ctx->ctor && !CONSTRUCTOR_PLACEHOLDER_BOUNDARY (ctx->ctor)) + if (tree outer_ob = lookup_placeholder (ctx->parent, lval, type)) + return outer_ob; + /* We could use ctx->object unconditionally, but using ctx->ctor when we can is a minor optimization. */ if (!lval && ctx->ctor && same_type_p (TREE_TYPE (ctx->ctor), type)) @@ -5606,19 +5618,16 @@ cxx_eval_constant_expression (const constexpr_ctx *ctx, tree t, r = *p; break; } - tree init = TARGET_EXPR_INITIAL (t); if ((AGGREGATE_TYPE_P (type) || VECTOR_TYPE_P (type))) { - if (ctx->object) - /* If the initializer contains any PLACEHOLDER_EXPR, we need to - resolve them before we create a new CONSTRUCTOR for the - temporary. */ - init = replace_placeholders (init, ctx->object); - /* We're being expanded without an explicit target, so start initializing a new object; expansion with an explicit target strips the TARGET_EXPR before we get here. */ new_ctx = *ctx; + /* Link CTX to NEW_CTX so that lookup_placeholder can resolve + any PLACEHOLDER_EXPR within the initializer that refers to the + former object under construction. */ + new_ctx.parent = ctx; new_ctx.ctor = build_constructor (type, NULL); CONSTRUCTOR_NO_CLEARING (new_ctx.ctor) = true; new_ctx.object = slot; @@ -6472,7 +6481,7 @@ cxx_eval_outermost_constant_expr (tree t, bool allow_non_constant, bool overflow_p = false; constexpr_global_ctx global_ctx; - constexpr_ctx ctx = { &global_ctx, NULL, NULL, NULL, NULL, NULL, + constexpr_ctx ctx = { &global_ctx, NULL, NULL, NULL, NULL, NULL, NULL, allow_non_constant, strict, manifestly_const_eval || !allow_non_constant, uid_sensitive }; |