From: Jakub Jelinek <jakub@redhat.com>
Date: Thu, 23 Apr 2020 19:57:50 +0000 (+0200)
Subject: Shortcut identity VEC_PERM expansion [PR94710]
X-Git-Tag: releases/gcc-9.4.0~679
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=15e2cca37186c848d12f4a0bb9ebcb8be32ed9de;p=thirdparty%2Fgcc.git

Shortcut identity VEC_PERM expansion [PR94710]

This PR is about the rs6000 backend emitting wrong assembly
for whole vector shift by 0, and while I think it is desirable
to fix the backend, I don't see a point why the expander should
try to emit that, whole vector shift by 0 is identity, we can just
return the operand.

2020-04-23  Jakub Jelinek  <jakub@redhat.com>

	PR target/94710
	* optabs.c (expand_vec_perm_const): For shift_amt const0_rtx
	just return v2.

(cherry picked from commit f51be2fb8653f81092f8158a0f0527275f86603b)
---

diff --git a/gcc/optabs.c b/gcc/optabs.c
index 7d7efe0a4a27..f469e8099392 100644
--- a/gcc/optabs.c
+++ b/gcc/optabs.c
@@ -5559,6 +5559,8 @@ expand_vec_perm_const (machine_mode mode, rtx v0, rtx v1,
       if (shift_amt)
 	{
 	  struct expand_operand ops[3];
+	  if (shift_amt == const0_rtx)
+	    return v0;
 	  if (shift_code != CODE_FOR_nothing)
 	    {
 	      create_output_operand (&ops[0], target, mode);