[gcc r12-7822] reload: Adjust comment in find_reloads about subset, not intersection

[gcc r12-7822] reload: Adjust comment in find_reloads about subset, not intersection

[Hans-Peter Nilsson]

https://gcc.gnu.org/g:75d1c8fea9541dee5a4ce0aa7d8c199574fd42b9

commit r12-7822-g75d1c8fea9541dee5a4ce0aa7d8c199574fd42b9
Author: Hans-Peter Nilsson <hp@axis.com>
Date:   Sat Mar 26 05:31:22 2022 +0100

    reload: Adjust comment in find_reloads about subset, not intersection
    
    gcc:
            * reload.cc (find_reloads): Align comment with code where
            considering the intersection of register classes then tweaking the
            regclass for the current alternative or rejecting it.

Diff:
---
 gcc/reload.cc | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/gcc/reload.cc b/gcc/reload.cc
index 664082a533d..3ed901e3944 100644
--- a/gcc/reload.cc
+++ b/gcc/reload.cc
@@ -3635,9 +3635,11 @@ find_reloads (rtx_insn *insn, int replace, int ind_levels, int live_known,
 		 a hard reg and this alternative accepts some
 		 register, see if the class that we want is a subset
 		 of the preferred class for this register.  If not,
-		 but it intersects that class, use the preferred class
-		 instead.  If it does not intersect the preferred
-		 class, show that usage of this alternative should be
+		 but it intersects that class, we'd like to use the
+		 intersection, but the best we can do is to use the
+		 preferred class, if it is instead a subset of the
+		 class we want in this alternative.  If we can't use
+		 it, show that usage of this alternative should be
 		 discouraged; it will be discouraged more still if the
 		 register is `preferred or nothing'.  We do this
 		 because it increases the chance of reusing our spill
@@ -3664,9 +3666,10 @@ find_reloads (rtx_insn *insn, int replace, int ind_levels, int live_known,
 		  if (! reg_class_subset_p (this_alternative[i],
 					    preferred_class[i]))
 		    {
-		      /* Since we don't have a way of forming the intersection,
-			 we just do something special if the preferred class
-			 is a subset of the class we have; that's the most
+		      /* Since we don't have a way of forming a register
+			 class for the intersection, we just do
+			 something special if the preferred class is a
+			 subset of the class we have; that's the most
 			 common case anyway.  */
 		      if (reg_class_subset_p (preferred_class[i],
 					      this_alternative[i]))