[gcc r12-9930] lra: Avoid unfolded plus-0

[gcc r12-9930] lra: Avoid unfolded plus-0

[Richard Sandiford]

https://gcc.gnu.org/g:6a527b809f99d3f05df16f792b2de6b32fa0d579

commit r12-9930-g6a527b809f99d3f05df16f792b2de6b32fa0d579
Author: Richard Sandiford <richard.sandiford@arm.com>
Date:   Thu Oct 19 10:49:19 2023 +0100

    lra: Avoid unfolded plus-0
    
    While backporting another patch to an earlier release, I hit a
    situation in which lra_eliminate_regs_1 would eliminate an address to:
    
        (plus (reg:P R) (const_int 0))
    
    This address compared not-equal to plain:
    
        (reg:P R)
    
    which caused an ICE in a later peephole2.  (The ICE showed up in
    gfortran.fortran-torture/compile/pr80464.f90 on the branch but seems
    to be latent on trunk.)
    
    These unfolded PLUSes shouldn't occur in the insn stream, and later code
    in the same function tried to avoid them.
    
    gcc/
            PR target/111528
            * lra-eliminations.cc (lra_eliminate_regs_1): Use simplify_gen_binary
            rather than gen_rtx_PLUS.
    
    (cherry picked from commit 10d59b802a7db9ae908291fb20627c1493cfa26c)

Diff:
---
 gcc/lra-eliminations.cc | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/gcc/lra-eliminations.cc b/gcc/lra-eliminations.cc
index c630ff4af2d1..7642d9857a87 100644
--- a/gcc/lra-eliminations.cc
+++ b/gcc/lra-eliminations.cc
@@ -397,8 +397,8 @@ lra_eliminate_regs_1 (rtx_insn *insn, rtx x, machine_mode mem_mode,
 	      rtx to = subst_p ? ep->to_rtx : ep->from_rtx;
 
 	      if (! update_p && ! full_p)
-		return gen_rtx_PLUS (Pmode, to, XEXP (x, 1));
-	      
+		return simplify_gen_binary (PLUS, Pmode, to, XEXP (x, 1));
+
 	      if (maybe_ne (update_sp_offset, 0))
 		offset = ep->to_rtx == stack_pointer_rtx ? update_sp_offset : 0;
 	      else