[gcc r16-2144] Make the RTL frontend set REG_NREGS correctly

[Richard Sandiford via Gcc-cvs]

https://gcc.gnu.org/g:76db38d811a63a603deedfe327d5e201fc820444

commit r16-2144-g76db38d811a63a603deedfe327d5e201fc820444
Author: Richard Sandiford <richard.sandif...@arm.com>
Date:   Wed Jul 9 16:39:20 2025 +0100

    Make the RTL frontend set REG_NREGS correctly
    
    While working on a new testcase that uses the RTL frontend,
    I hit a bug where a (reg ...) that spans multiple hard registers
    had REG_NREGS set to 1.  This caused various things to misbehave.
    For example, if the (reg ...) in question was used as crtl->return_rtx,
    only the first register in the group would be marked as live on exit.
    
    gcc/
            * read-rtl-function.cc (function_reader::read_rtx_operand_r): Use
            hard_regno_nregs to work out REG_NREGS for hard registers.

Diff:
---
 gcc/read-rtl-function.cc | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/gcc/read-rtl-function.cc b/gcc/read-rtl-function.cc
index fb9c9554ea30..1f08c50cc128 100644
--- a/gcc/read-rtl-function.cc
+++ b/gcc/read-rtl-function.cc
@@ -1065,7 +1065,10 @@ function_reader::read_rtx_operand_r (rtx x)
   if (regno == -1)
     fatal_at (loc, "unrecognized register: '%s'", name.string);
 
-  set_regno_raw (x, regno, 1);
+  int nregs = 1;
+  if (HARD_REGISTER_NUM_P (regno))
+    nregs = hard_regno_nregs (regno, GET_MODE (x));
+  set_regno_raw (x, regno, nregs);
 
   /* Consolidate singletons.  */
   x = consolidate_singletons (x);