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-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=f51be2fb8653f81092f8158a0f0527275f86603b;p=gcc.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.
---

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 5ddb4332047..54e207cbe58 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,5 +1,9 @@
 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.
+
 	PR middle-end/94724
 	* tree.c (get_narrower): Instead of creating COMPOUND_EXPRs
 	temporarily with non-final second operand and updating it later,
diff --git a/gcc/optabs.c b/gcc/optabs.c
index 1456e59ffa7..d85ce47f762 100644
--- a/gcc/optabs.c
+++ b/gcc/optabs.c
@@ -5627,6 +5627,8 @@ expand_vec_perm_const (machine_mode mode, rtx v0, rtx v1,
       if (shift_amt)
 	{
 	  class expand_operand ops[3];
+	  if (shift_amt == const0_rtx)
+	    return v2;
 	  if (shift_code != CODE_FOR_nothing)
 	    {
 	      create_output_operand (&ops[0], target, mode);