From: Robin Dapp <rdapp@ventanamicro.com>
Date: Fri, 7 Nov 2025 09:21:36 +0000 (+0100)
Subject: optabs: Do not pun modes smaller than QImode.
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=a17e06fa2ab5776de129d35418e05039bd9a51b1;p=thirdparty%2Fgcc.git

optabs: Do not pun modes smaller than QImode.

In can_vec_perm_const_p if we cannot directly permute a vector mode we
try to pun it with a byte mode.  qimode_for_vec_perm checks gets the
mode size and uses that as number of elements for the new QImode vector.

This doesn't work for RVV mask vectors, though.  First, their
precision might be smaller than a byte and second, there is no
way to easily pun them.  The most common way would be a vector select
from {0, 0, ...} and {1, 1, ...} vectors.  Therefore this patch checks
if the perm's innermode precision is a multiple of QImode's precision.

Bootstrapped and regtested on x86 and power10.  Regtested on aarch64 and
riscv64.

gcc/ChangeLog:

	* optabs-query.cc (qimode_for_vec_perm): Check if QImode's
	precision divides the inner mode's precision.
---

diff --git a/gcc/optabs-query.cc b/gcc/optabs-query.cc
index 5335d0d8401..484d7c2e205 100644
--- a/gcc/optabs-query.cc
+++ b/gcc/optabs-query.cc
@@ -358,7 +358,9 @@ can_conditionally_move_p (machine_mode mode)
 opt_machine_mode
 qimode_for_vec_perm (machine_mode mode)
 {
-  if (GET_MODE_INNER (mode) != QImode)
+  if (GET_MODE_INNER (mode) != QImode
+      && multiple_p (GET_MODE_PRECISION (GET_MODE_INNER (mode)),
+		     GET_MODE_PRECISION (QImode)))
     return related_vector_mode (mode, QImode, GET_MODE_SIZE (mode));
   return opt_machine_mode ();
 }