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 --git a/gcc/lra-eliminations.cc b/gcc/lra-eliminations.cc
index c630ff4af2d141f8733c7255cc9ba1a3b9a6d994..7642d9857a8726171e8e216139eb2e343d5a07a8 100644 (file)
--- 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