On 2/9/23 09:36, Patrick Palka wrote:
On Sun, 5 Feb 2023, Jason Merrill wrote:On 2/3/23 15:51, Patrick Palka wrote:On Mon, 30 Jan 2023, Jason Merrill wrote:On 1/27/23 17:02, Patrick Palka wrote:This PR illustrates that __builtin_is_constant_evaluated currently acts as an optimization barrier for our speculative constexpr evaluation, since we don't want to prematurely fold the builtin to false if the expression in question would be later manifestly constant evaluated (in which case it must be folded to true). This patch fixes this by permitting __builtin_is_constant_evaluated to get folded as false during cp_fold_function, since at that point we're sure we're doing manifestly constant evaluation. To that end we add a flags parameter to cp_fold that controls what mce_value the CALL_EXPR case passes to maybe_constant_value. bootstrapped and rgetsted no x86_64-pc-linux-gnu, does this look OK for trunk? PR c++/108243 gcc/cp/ChangeLog: * cp-gimplify.cc (enum fold_flags): Define. (cp_fold_data::genericize): Replace this data member with ... (cp_fold_data::fold_flags): ... this. (cp_fold_r): Adjust cp_fold_data use and cp_fold_calls. (cp_fold_function): Likewise. (cp_fold_maybe_rvalue): Likewise. (cp_fully_fold_init): Likewise. (cp_fold): Add fold_flags parameter. Don't cache if flags isn't empty. <case CALL_EXPR>: Pass mce_false to maybe_constant_value if if ff_genericize is set. gcc/testsuite/ChangeLog: * g++.dg/opt/pr108243.C: New test. --- gcc/cp/cp-gimplify.cc | 76 ++++++++++++++++++----------- gcc/testsuite/g++.dg/opt/pr108243.C | 29 +++++++++++ 2 files changed, 76 insertions(+), 29 deletions(-) create mode 100644 gcc/testsuite/g++.dg/opt/pr108243.C diff --git a/gcc/cp/cp-gimplify.cc b/gcc/cp/cp-gimplify.cc index a35cedd05cc..d023a63768f 100644 --- a/gcc/cp/cp-gimplify.cc +++ b/gcc/cp/cp-gimplify.cc @@ -43,12 +43,20 @@ along with GCC; see the file COPYING3. If not see #include "omp-general.h" #include "opts.h" +/* Flags for cp_fold and cp_fold_r. */ + +enum fold_flags { + ff_none = 0, + /* Whether we're being called from cp_fold_function. */ + ff_genericize = 1 << 0, +}; + /* Forward declarations. */ static tree cp_genericize_r (tree *, int *, void *); static tree cp_fold_r (tree *, int *, void *); static void cp_genericize_tree (tree*, bool); -static tree cp_fold (tree); +static tree cp_fold (tree, fold_flags); /* Genericize a TRY_BLOCK. */ @@ -996,9 +1004,8 @@ struct cp_genericize_data struct cp_fold_data { hash_set<tree> pset; - bool genericize; // called from cp_fold_function? - - cp_fold_data (bool g): genericize (g) {} + fold_flags flags; + cp_fold_data (fold_flags flags): flags (flags) {} }; static tree @@ -1039,7 +1046,7 @@ cp_fold_r (tree *stmt_p, int *walk_subtrees, void *data_) break; } - *stmt_p = stmt = cp_fold (*stmt_p); + *stmt_p = stmt = cp_fold (*stmt_p, data->flags); if (data->pset.add (stmt)) { @@ -1119,12 +1126,12 @@ cp_fold_r (tree *stmt_p, int *walk_subtrees, void *data_) here rather than in cp_genericize to avoid problems with the invisible reference transition. */ case INIT_EXPR: - if (data->genericize) + if (data->flags & ff_genericize) cp_genericize_init_expr (stmt_p); break; case TARGET_EXPR: - if (data->genericize) + if (data->flags & ff_genericize) cp_genericize_target_expr (stmt_p); /* Folding might replace e.g. a COND_EXPR with a TARGET_EXPR; in @@ -1157,7 +1164,7 @@ cp_fold_r (tree *stmt_p, int *walk_subtrees, void *data_) void cp_fold_function (tree fndecl) { - cp_fold_data data (/*genericize*/true); + cp_fold_data data (ff_genericize); cp_walk_tree (&DECL_SAVED_TREE (fndecl), cp_fold_r, &data, NULL); } @@ -2375,7 +2382,7 @@ cp_fold_maybe_rvalue (tree x, bool rval) { while (true) { - x = cp_fold (x); + x = cp_fold (x, ff_none); if (rval) x = mark_rvalue_use (x); if (rval && DECL_P (x) @@ -2434,7 +2441,7 @@ cp_fully_fold_init (tree x) if (processing_template_decl) return x; x = cp_fully_fold (x); - cp_fold_data data (/*genericize*/false); + cp_fold_data data (ff_none); cp_walk_tree (&x, cp_fold_r, &data, NULL); return x; } @@ -2469,7 +2476,7 @@ clear_fold_cache (void) Function returns X or its folded variant. */ static tree -cp_fold (tree x) +cp_fold (tree x, fold_flags flags) { tree op0, op1, op2, op3; tree org_x = x, r = NULL_TREE; @@ -2490,8 +2497,11 @@ cp_fold (tree x) if (fold_cache == NULL) fold_cache = hash_map<tree, tree>::create_ggc (101); - if (tree *cached = fold_cache->get (x)) - return *cached; + bool cache_p = (flags == ff_none); + + if (cache_p) + if (tree *cached = fold_cache->get (x)) + return *cached; uid_sensitive_constexpr_evaluation_checker c; @@ -2526,7 +2536,7 @@ cp_fold (tree x) Don't create a new tree if op0 != TREE_OPERAND (x, 0), the folding of the operand should be in the caches and if in cp_fold_r it will modify it in place. */ - op0 = cp_fold (TREE_OPERAND (x, 0)); + op0 = cp_fold (TREE_OPERAND (x, 0), flags); if (op0 == error_mark_node) x = error_mark_node; break; @@ -2571,7 +2581,7 @@ cp_fold (tree x) { tree p = maybe_undo_parenthesized_ref (x); if (p != x) - return cp_fold (p); + return cp_fold (p, flags); } goto unary; @@ -2763,8 +2773,8 @@ cp_fold (tree x) case COND_EXPR: loc = EXPR_LOCATION (x); op0 = cp_fold_rvalue (TREE_OPERAND (x, 0)); - op1 = cp_fold (TREE_OPERAND (x, 1)); - op2 = cp_fold (TREE_OPERAND (x, 2)); + op1 = cp_fold (TREE_OPERAND (x, 1), flags); + op2 = cp_fold (TREE_OPERAND (x, 2), flags); if (TREE_CODE (TREE_TYPE (x)) == BOOLEAN_TYPE) { @@ -2854,7 +2864,7 @@ cp_fold (tree x) { if (!same_type_p (TREE_TYPE (x), TREE_TYPE (r))) r = build_nop (TREE_TYPE (x), r); - x = cp_fold (r); + x = cp_fold (r, flags); break; } } @@ -2908,7 +2918,7 @@ cp_fold (tree x) int m = call_expr_nargs (x); for (int i = 0; i < m; i++) { - r = cp_fold (CALL_EXPR_ARG (x, i)); + r = cp_fold (CALL_EXPR_ARG (x, i), flags); if (r != CALL_EXPR_ARG (x, i)) { if (r == error_mark_node) @@ -2931,7 +2941,7 @@ cp_fold (tree x) if (TREE_CODE (r) != CALL_EXPR) { - x = cp_fold (r); + x = cp_fold (r, flags); break; } @@ -2944,7 +2954,15 @@ cp_fold (tree x) constant, but the call followed by an INDIRECT_REF is. */ if (callee && DECL_DECLARED_CONSTEXPR_P (callee) && !flag_no_inline) - r = maybe_constant_value (x); + { + mce_value manifestly_const_eval = mce_unknown; + if (flags & ff_genericize) + /* At genericization time it's safe to fold + __builtin_is_constant_evaluated to false. */ + manifestly_const_eval = mce_false; + r = maybe_constant_value (x, /*decl=*/NULL_TREE, + manifestly_const_eval); + } optimize = sv; if (TREE_CODE (r) != CALL_EXPR) @@ -2971,7 +2989,7 @@ cp_fold (tree x) vec<constructor_elt, va_gc> *nelts = NULL; FOR_EACH_VEC_SAFE_ELT (elts, i, p) { - tree op = cp_fold (p->value); + tree op = cp_fold (p->value, flags); if (op != p->value) { if (op == error_mark_node) @@ -3002,7 +3020,7 @@ cp_fold (tree x) for (int i = 0; i < n; i++) { - tree op = cp_fold (TREE_VEC_ELT (x, i)); + tree op = cp_fold (TREE_VEC_ELT (x, i), flags); if (op != TREE_VEC_ELT (x, i)) { if (!changed) @@ -3019,10 +3037,10 @@ cp_fold (tree x) case ARRAY_RANGE_REF: loc = EXPR_LOCATION (x); - op0 = cp_fold (TREE_OPERAND (x, 0)); - op1 = cp_fold (TREE_OPERAND (x, 1)); - op2 = cp_fold (TREE_OPERAND (x, 2)); - op3 = cp_fold (TREE_OPERAND (x, 3)); + op0 = cp_fold (TREE_OPERAND (x, 0), flags); + op1 = cp_fold (TREE_OPERAND (x, 1), flags); + op2 = cp_fold (TREE_OPERAND (x, 2), flags); + op3 = cp_fold (TREE_OPERAND (x, 3), flags); if (op0 != TREE_OPERAND (x, 0) || op1 != TREE_OPERAND (x, 1) @@ -3050,7 +3068,7 @@ cp_fold (tree x) /* A SAVE_EXPR might contain e.g. (0 * i) + (0 * j), which, after folding, evaluates to an invariant. In that case no need to wrap this folded tree with a SAVE_EXPR. */ - r = cp_fold (TREE_OPERAND (x, 0)); + r = cp_fold (TREE_OPERAND (x, 0), flags); if (tree_invariant_p (r)) x = r; break; @@ -3069,7 +3087,7 @@ cp_fold (tree x) copy_warning (x, org_x); } - if (!c.evaluation_restricted_p ()) + if (cache_p && !c.evaluation_restricted_p ()) { fold_cache->put (org_x, x); /* Prevent that we try to fold an already folded result again. */ diff --git a/gcc/testsuite/g++.dg/opt/pr108243.C b/gcc/testsuite/g++.dg/opt/pr108243.C new file mode 100644 index 00000000000..4c45dbba13c --- /dev/null +++ b/gcc/testsuite/g++.dg/opt/pr108243.C @@ -0,0 +1,29 @@ +// PR c++/108243 +// { dg-do compile { target c++11 } } +// { dg-additional-options "-O -fdump-tree-original" } + +constexpr int foo() { + return __builtin_is_constant_evaluated() + 1; +} + +#if __cpp_if_consteval +constexpr int bar() { + if consteval { + return 5; + } else { + return 4; + } +} +#endif + +int p, q; + +int main() { + p = foo(); +#if __cpp_if_consteval + q = bar(); +#endif +} + +// { dg-final { scan-tree-dump-not "= foo" "original" } } +// { dg-final { scan-tree-dump-not "= bar" "original" } }Let's also test a static initializer that can't be fully constant-evaluated.D'oh, doing so revealed that cp_fold_function doesn't reach static initializers; that's taken care of by cp_fully_fold_init. So it seems we need to make cp_fold when called from the latter entry point to also assume m_c_e is false. We can't re-use ff_genericize here because that flag has additional effects in cp_fold_r, so it seems we need another flag that that only affects the manifestly constant-eval stuff; I called it ff_mce_false. How does the following look? -- >8 -- Subject: [PATCH 2/2] c++: speculative constexpr and is_constant_evaluated [PR108243] This PR illustrates that __builtin_is_constant_evaluated currently acts as an optimization barrier for our speculative constexpr evaluation, since we don't want to prematurely fold the builtin to false if the expression in question would be later manifestly constant evaluated (in which case it must be folded to true). This patch fixes this by permitting __builtin_is_constant_evaluated to get folded as false during cp_fold_function and cp_fully_fold_init, since at these points we're sure we're done with manifestly constant evaluation. To that end we add a flags parameter to cp_fold that controls whether we pass mce_false or mce_unknown to maybe_constant_value when folding a CALL_EXPR. PR c++/108243 PR c++/97553 gcc/cp/ChangeLog: * cp-gimplify.cc (enum fold_flags): Define. (cp_fold_data::genericize): Replace this data member with ... (cp_fold_data::fold_flags): ... this. (cp_fold_r): Adjust use of cp_fold_data and calls to cp_fold. (cp_fold_function): Likewise. (cp_fold_maybe_rvalue): Likewise. (cp_fully_fold_init): Likewise. (cp_fold): Add fold_flags parameter. Don't cache if flags isn't empty. <case CALL_EXPR>: If ff_genericize is set, fold __builtin_is_constant_evaluated to false and pass mce_false to maybe_constant_value. gcc/testsuite/ChangeLog: * g++.dg/opt/is_constant_evaluated1.C: New test. * g++.dg/opt/is_constant_evaluated2.C: New test. --- gcc/cp/cp-gimplify.cc | 88 ++++++++++++------- .../g++.dg/opt/is_constant_evaluated1.C | 14 +++ .../g++.dg/opt/is_constant_evaluated2.C | 32 +++++++ 3 files changed, 104 insertions(+), 30 deletions(-) create mode 100644 gcc/testsuite/g++.dg/opt/is_constant_evaluated1.C create mode 100644 gcc/testsuite/g++.dg/opt/is_constant_evaluated2.C diff --git a/gcc/cp/cp-gimplify.cc b/gcc/cp/cp-gimplify.cc index 9929d29981a..590ed787997 100644 --- a/gcc/cp/cp-gimplify.cc +++ b/gcc/cp/cp-gimplify.cc @@ -43,12 +43,26 @@ along with GCC; see the file COPYING3. If not see #include "omp-general.h" #include "opts.h" +/* Flags for cp_fold and cp_fold_r. */ + +enum fold_flags { + ff_none = 0, + /* Whether we're being called from cp_fold_function. */ + ff_genericize = 1 << 0, + /* Whether we're folding late enough that we could assume + we're definitely not in a manifestly constant-evaluated + context. */It's not necessarily a matter of late enough; we could fold sooner and still know that, as in cp_fully_fold_init. We could do the same at other full-expression points, but we don't because we want to delay folding as much as possible. So let's say "folding at a point where we know we're..."+ ff_mce_false = 1 << 1, +}; + +using fold_flags_t = int; + /* Forward declarations. */ static tree cp_genericize_r (tree *, int *, void *); static tree cp_fold_r (tree *, int *, void *); static void cp_genericize_tree (tree*, bool); -static tree cp_fold (tree); +static tree cp_fold (tree, fold_flags_t); /* Genericize a TRY_BLOCK. */ @@ -1012,9 +1026,8 @@ struct cp_genericize_data struct cp_fold_data { hash_set<tree> pset; - bool genericize; // called from cp_fold_function? - - cp_fold_data (bool g): genericize (g) {} + fold_flags_t flags; + cp_fold_data (fold_flags_t flags): flags (flags) {} }; static tree @@ -1055,7 +1068,7 @@ cp_fold_r (tree *stmt_p, int *walk_subtrees, void *data_) break; } - *stmt_p = stmt = cp_fold (*stmt_p); + *stmt_p = stmt = cp_fold (*stmt_p, data->flags); if (data->pset.add (stmt)) { @@ -1135,12 +1148,12 @@ cp_fold_r (tree *stmt_p, int *walk_subtrees, void *data_) here rather than in cp_genericize to avoid problems with the invisible reference transition. */ case INIT_EXPR: - if (data->genericize) + if (data->flags & ff_genericize) cp_genericize_init_expr (stmt_p); break; case TARGET_EXPR: - if (data->genericize) + if (data->flags & ff_genericize) cp_genericize_target_expr (stmt_p); /* Folding might replace e.g. a COND_EXPR with a TARGET_EXPR; in @@ -1173,7 +1186,7 @@ cp_fold_r (tree *stmt_p, int *walk_subtrees, void *data_) void cp_fold_function (tree fndecl) { - cp_fold_data data (/*genericize*/true); + cp_fold_data data (ff_genericize | ff_mce_false);Here would be a good place for a comment about passing mce_false because all manifestly-constant-evaluated expressions will have been constant-evaluated already if possible.cp_walk_tree (&DECL_SAVED_TREE (fndecl), cp_fold_r, &data, NULL); } @@ -2391,7 +2404,7 @@ cp_fold_maybe_rvalue (tree x, bool rval) { while (true) { - x = cp_fold (x); + x = cp_fold (x, ff_none); if (rval) x = mark_rvalue_use (x); if (rval && DECL_P (x) @@ -2450,7 +2463,7 @@ cp_fully_fold_init (tree x) if (processing_template_decl) return x; x = cp_fully_fold (x); - cp_fold_data data (/*genericize*/false); + cp_fold_data data (ff_mce_false); cp_walk_tree (&x, cp_fold_r, &data, NULL); return x; } @@ -2485,7 +2498,7 @@ clear_fold_cache (void) Function returns X or its folded variant. */ static tree -cp_fold (tree x) +cp_fold (tree x, fold_flags_t flags) { tree op0, op1, op2, op3; tree org_x = x, r = NULL_TREE; @@ -2506,8 +2519,11 @@ cp_fold (tree x) if (fold_cache == NULL) fold_cache = hash_map<tree, tree>::create_ggc (101); - if (tree *cached = fold_cache->get (x)) - return *cached; + bool cache_p = (flags == ff_none); + + if (cache_p) + if (tree *cached = fold_cache->get (x)) + return *cached; uid_sensitive_constexpr_evaluation_checker c; @@ -2542,7 +2558,7 @@ cp_fold (tree x) Don't create a new tree if op0 != TREE_OPERAND (x, 0), the folding of the operand should be in the caches and if in cp_fold_r it will modify it in place. */ - op0 = cp_fold (TREE_OPERAND (x, 0)); + op0 = cp_fold (TREE_OPERAND (x, 0), flags); if (op0 == error_mark_node) x = error_mark_node; break; @@ -2587,7 +2603,7 @@ cp_fold (tree x) { tree p = maybe_undo_parenthesized_ref (x); if (p != x) - return cp_fold (p); + return cp_fold (p, flags); } goto unary; @@ -2779,8 +2795,8 @@ cp_fold (tree x) case COND_EXPR: loc = EXPR_LOCATION (x); op0 = cp_fold_rvalue (TREE_OPERAND (x, 0)); - op1 = cp_fold (TREE_OPERAND (x, 1)); - op2 = cp_fold (TREE_OPERAND (x, 2)); + op1 = cp_fold (TREE_OPERAND (x, 1), flags); + op2 = cp_fold (TREE_OPERAND (x, 2), flags); if (TREE_CODE (TREE_TYPE (x)) == BOOLEAN_TYPE) { @@ -2870,7 +2886,7 @@ cp_fold (tree x) { if (!same_type_p (TREE_TYPE (x), TREE_TYPE (r))) r = build_nop (TREE_TYPE (x), r); - x = cp_fold (r); + x = cp_fold (r, flags); break; } } @@ -2890,8 +2906,12 @@ cp_fold (tree x) { switch (DECL_FE_FUNCTION_CODE (callee)) { - /* Defer folding __builtin_is_constant_evaluated. */ case CP_BUILT_IN_IS_CONSTANT_EVALUATED: + /* Defer folding __builtin_is_constant_evaluated unless + we can assume this isn't a manifestly constant-evaluateds/can assume/know/ OK with those comment changes.Thanks a lot. Unfortunately I think the patch has a significant problem that only just occurred to me -- disabling the cp_fold cache when the flag ff_mce_false is set effectively makes cp_fold_function and cp_fully_fold_init quadratic in the size of the expression (since cp_fold_r calls cp_fold on each subtree, and cp_fold when the cache is disabled will end up fully walking each subtree). Note that the reason we must disable the cache is because cp_fold with ff_mce_false might give a different folded result than without that flag if the expression contains a suitable CALL_EXPR subexpression.
Good point.
One approach to fix this complexity issue would be to parameterize the cache according to the flags that were passed to cp_fold, which would allow us to keep the cache enabled when ff_mce_false is set. A downside to this approach is that the size of the cp_fold cache would essentially double since for each tree we'd now have two cache entries, one for flags=ff_none and another for flags=ff_mce_false.
We could also clear the cache before cp_fold_function since the two folds shouldn't overlap (much).
Another approach would be to split out the trial constexpr evaluation part of cp_fold's CALL_EXPR handling, parameterize that, and call it directly from cp_fold_r. With this approach we wouldn't perform as much folding, e.g. int n = 41 + !std::is_constant_evaluated(); would get folded to 1 + 41 rather than 42. But I suspect this would give us 95% of the reapable benefits of the above approach. I think I'm leaning towards this second approach, which the below patch implements instead. What do you think? Bootstrapped and regtested on x86_64-pc-linux-gnu.
That sounds reasonable, but...
-- >8 -- Subject: [PATCH] c++: speculative constexpr and is_constant_evaluated [PR108243] This PR illustrates that __builtin_is_constant_evaluated currently acts as an optimization barrier for our speculative constexpr evaluation, since we don't want to prematurely fold the builtin to false before the expression in question undergoes constant evaluation as in a manifestly constant-evaluated context (in which case the builtin must instead be folded to true). This patch fixes this by permitting __builtin_is_constant_evaluated to get folded to false from cp_fold_r, where we know we're done with proper constant evaluation (of manifestly constant-evaluated contexts). PR c++/108243 PR c++/97553 gcc/cp/ChangeLog: * cp-gimplify.cc (cp_fold_r): Remove redundant *stmt_p assignments. After calling cp_fold, call maybe_fold_constexpr_call with mce_false. (cp_fold) <case CALL_EXPR>: Split out trial constexpr evaluation into ... (maybe_fold_constexpr_call): ... here. gcc/testsuite/ChangeLog: * g++.dg/opt/is_constant_evaluated1.C: New test. * g++.dg/opt/is_constant_evaluated2.C: New test. --- gcc/cp/cp-gimplify.cc | 55 +++++++++++++++---- .../g++.dg/opt/is_constant_evaluated1.C | 20 +++++++ .../g++.dg/opt/is_constant_evaluated2.C | 32 +++++++++++ 3 files changed, 95 insertions(+), 12 deletions(-) create mode 100644 gcc/testsuite/g++.dg/opt/is_constant_evaluated1.C create mode 100644 gcc/testsuite/g++.dg/opt/is_constant_evaluated2.C diff --git a/gcc/cp/cp-gimplify.cc b/gcc/cp/cp-gimplify.cc index 9929d29981a..dca55056b2c 100644 --- a/gcc/cp/cp-gimplify.cc +++ b/gcc/cp/cp-gimplify.cc @@ -49,6 +49,7 @@ static tree cp_genericize_r (tree *, int *, void *); static tree cp_fold_r (tree *, int *, void *); static void cp_genericize_tree (tree*, bool); static tree cp_fold (tree); +static tree maybe_fold_constexpr_call (tree, mce_value);/* Genericize a TRY_BLOCK. */ @@ -1034,7 +1035,7 @@ cp_fold_r (tree *stmt_p, int *walk_subtrees, void *data_)error_at (PTRMEM_CST_LOCATION (stmt), "taking address of an immediate function %qD", PTRMEM_CST_MEMBER (stmt)); - stmt = *stmt_p = build_zero_cst (TREE_TYPE (stmt)); + stmt = build_zero_cst (TREE_TYPE (stmt)); break; } break; @@ -1046,7 +1047,7 @@ cp_fold_r (tree *stmt_p, int *walk_subtrees, void *data_) error_at (EXPR_LOCATION (stmt), "taking address of an immediate function %qD", TREE_OPERAND (stmt, 0)); - stmt = *stmt_p = build_zero_cst (TREE_TYPE (stmt)); + stmt = build_zero_cst (TREE_TYPE (stmt)); break; } break; @@ -1055,7 +1056,17 @@ cp_fold_r (tree *stmt_p, int *walk_subtrees, void *data_) break; }- *stmt_p = stmt = cp_fold (*stmt_p);+ stmt = cp_fold (stmt); + + if (TREE_CODE (stmt) == CALL_EXPR) + /* Since cp_fold_r is called (from cp_genericize, cp_fold_function + and cp_fully_fold_init) only after the overall expression has been + considered for constant-evaluation, we can by now safely fold any + remaining __builtin_is_constant_evaluated calls to false, so try + constexpr expansion with mce_false. */ + stmt = maybe_fold_constexpr_call (stmt, mce_false); + + *stmt_p = stmt;if (data->pset.add (stmt)){ @@ -2952,15 +2963,10 @@ cp_fold (tree x) }optimize = nw;- - /* Invoke maybe_constant_value for functions declared - constexpr and not called with AGGR_INIT_EXPRs. - TODO: - Do constexpr expansion of expressions where the call itself is not - constant, but the call followed by an INDIRECT_REF is. */ - if (callee && DECL_DECLARED_CONSTEXPR_P (callee) - && !flag_no_inline) - r = maybe_constant_value (x); + /* Pass mce_unknown to defer folding __builtin_is_constant_evaluated + since we don't know if we're in a manifestly constant-evaluated + context that hasn't yet been constant-evaluated. */ + r = maybe_fold_constexpr_call (x, mce_unknown);
It seems unfortunate to try to fold both here and in cp_fold_r.Does this patch still fold __builtin_is_constant_evaluated() even though it no longer touches the cp_fold builtin handling?
optimize = sv;if (TREE_CODE (r) != CALL_EXPR)@@ -3096,6 +3102,31 @@ cp_fold (tree x) return x; }+/* If the CALL_EXPR X calls a constexpr function, try expanding it via+ constexpr evaluation. Returns the expanded result or X if constexpr + evaluation wasn't possible. + + TODO: Do constexpr expansion of expressions where the call itself + is not constant, but the call followed by an INDIRECT_REF is. */ + +static tree +maybe_fold_constexpr_call (tree x, mce_value manifestly_const_eval) +{ + if (flag_no_inline) + return x; + tree callee = get_callee_fndecl (x); + if (!callee) + return x; + if (DECL_DECLARED_CONSTEXPR_P (callee)) + { + tree r = maybe_constant_value (x, /*decl=*/NULL_TREE, + manifestly_const_eval); + if (TREE_CODE (r) != CALL_EXPR) + return r; + } + return x; +} + /* Look up "hot", "cold", "likely" or "unlikely" in attribute list LIST. */treediff --git a/gcc/testsuite/g++.dg/opt/is_constant_evaluated1.C b/gcc/testsuite/g++.dg/opt/is_constant_evaluated1.C new file mode 100644 index 00000000000..2123f20e3e5 --- /dev/null +++ b/gcc/testsuite/g++.dg/opt/is_constant_evaluated1.C @@ -0,0 +1,20 @@ +// PR c++/108243 +// { dg-do compile { target c++11 } } +// { dg-additional-options "-O -fdump-tree-original" } + +struct A { + constexpr A(int n, int m) : n(n), m(m) { } + int n, m; +}; + +constexpr int foo(int n) { + return n + !__builtin_is_constant_evaluated(); +} + +A* f(int n) { + static A a = {n, foo(41)}; + return &a; +} + +// { dg-final { scan-tree-dump "42" "original" } } +// { dg-final { scan-tree-dump-not "foo \\(41\\)" "original" } } diff --git a/gcc/testsuite/g++.dg/opt/is_constant_evaluated2.C b/gcc/testsuite/g++.dg/opt/is_constant_evaluated2.C new file mode 100644 index 00000000000..ed964e20a7a --- /dev/null +++ b/gcc/testsuite/g++.dg/opt/is_constant_evaluated2.C @@ -0,0 +1,32 @@ +// PR c++/97553 +// { dg-do compile { target c++11 } } +// { dg-additional-options "-O -fdump-tree-original" } + +constexpr int foo() { + return __builtin_is_constant_evaluated() + 1; +} + +#if __cpp_if_consteval +constexpr int bar() { + if consteval { + return 5; + } else { + return 4; + } +} +#endif + +int p, q; + +int main() { + p = foo(); +#if __cpp_if_consteval + q = bar(); +#endif +} + +// { dg-final { scan-tree-dump "p = 1" "original" } } +// { dg-final { scan-tree-dump-not "= foo" "original" } } + +// { dg-final { scan-tree-dump "q = 4" "original" { target c++23 } } } +// { dg-final { scan-tree-dump-not "= bar" "original" { target c++23 } } }
