[PATCH] lra: Avoid unfolded plus-0

[Richard Sandiford <richard.sandiford@arm.com>]

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.

Tested on aarch64-linux-gnu so far, but I'll test on x86_64-linux-gnu too.
Does this look OK?

There are probably other instances of the same thing elsewhere,
but it seemed safer to stick to the one that caused the issue.

Thanks,
Richard


gcc/
	* lra-eliminations.cc (lra_eliminate_regs_1): Use simplify_gen_binary
	rather than gen_rtx_PLUS.
---
 gcc/lra-eliminations.cc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/gcc/lra-eliminations.cc b/gcc/lra-eliminations.cc
index df613cdda76..4daaff1a124 100644
--- a/gcc/lra-eliminations.cc
+++ b/gcc/lra-eliminations.cc
@@ -406,7 +406,7 @@ lra_eliminate_regs_1 (rtx_insn *insn, rtx x, machine_mode mem_mode,
 		elimination_fp2sp_occured_p = true;
 
 	      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;
-- 
2.25.1