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From: Patrick Palka <>
Cc:, Patrick Palka <>
Subject: [PATCH] c++: redundant targ coercion for var/alias tmpls
Date: Wed, 21 Jun 2023 13:19:20 -0400	[thread overview]
Message-ID: <> (raw)

When stepping through the variable/alias template specialization code
paths, I noticed we perform template argument coercion twice: first from
instantiate_alias_template / finish_template_variable and again from
tsubst_decl (during instantiate_template).  It should suffice to perform
coercion once.

To that end patch elides this second coercion from tsubst_decl when
possible.  We can't get rid of it completely because we don't always
specialize a variable template from finish_template_variable: we could
also be doing so directly from instantiate_template during variable
template partial specialization selection, in which case the coercion
from tsubst_decl would be the first and only coercion.

Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
trunk?  This reduces memory usage of range-v3's zip.cpp by ~0.5%.


	* (tsubst_decl) <case TYPE_/VAR_DECL>: Call
	coercion_template_parms only if DECL_TEMPLATE_SPECIALIZATION
	is set.
 gcc/cp/ | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/gcc/cp/ b/gcc/cp/
index be86051abad..dd10409ce18 100644
--- a/gcc/cp/
+++ b/gcc/cp/
@@ -15232,10 +15232,17 @@ tsubst_decl (tree t, tree args, tsubst_flags_t complain)
 		argvec = tsubst (DECL_TI_ARGS (t), args, complain, in_decl);
 		if (argvec != error_mark_node
 		    && PRIMARY_TEMPLATE_P (gen_tmpl)
-		    && TMPL_ARGS_DEPTH (args) >= TMPL_ARGS_DEPTH (argvec))
-		  /* We're fully specializing a template declaration, so
-		     we need to coerce the innermost arguments corresponding to
-		     the template.  */
+		    && TMPL_ARGS_DEPTH (args) >= TMPL_ARGS_DEPTH (argvec)
+		  /* We're fully specializing an alias or variable template, so
+		     coerce the innermost arguments if necessary.  We expect
+		     instantiate_alias_template and finish_template_variable to
+		     already have done this relative to the primary template, in
+		     which case this coercion is unnecessary, but we can also
+		     get here when substituting a partial variable template
+		     specialization (directly from instantiate_template), in
+		     which case DECL_TEMPLATE_SPECIALIZATION is set and coercion
+		     is necessary.  */
 		  argvec = (coerce_template_parms
 			    (DECL_TEMPLATE_PARMS (gen_tmpl),
 			     argvec, tmpl, complain));

             reply	other threads:[~2023-06-21 17:19 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-06-21 17:19 Patrick Palka [this message]
2023-06-23 15:11 ` Jason Merrill
2023-06-23 16:23   ` Patrick Palka
2023-06-28 15:50     ` Jason Merrill
2023-06-28 20:14       ` Patrick Palka
2023-07-13 15:48         ` Patrick Palka
2023-07-13 20:44           ` Jason Merrill
2023-07-14 18:07             ` Patrick Palka
2023-07-14 21:17               ` Jason Merrill
2023-07-17 21:29                 ` Patrick Palka
2023-07-18 16:52                   ` Jason Merrill

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