From b4e8ceb98c4ec844b4886e61363a70e5a2c6b140 Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <hongjiu.lu@intel.com>
Date: Tue, 19 Aug 2014 16:26:35 +0000
Subject: [PATCH] Don't clear destination if it is used in source

	* config/i386/i386.md (*ctz<mode>2_falsedep_1): Don't clear
	destination if it is used in source.
	(*clz<mode>2_lzcnt_falsedep_1): Likewise.
	(*popcount<mode>2_falsedep_1): Likewise.

From-SVN: r214169
---
 gcc/ChangeLog           |  7 +++++++
 gcc/config/i386/i386.md | 24 ++++++++++++++++++------
 2 files changed, 25 insertions(+), 6 deletions(-)

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 07516816bb19..01597a4c3255 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,10 @@
+2014-08-19  H.J. Lu  <hongjiu.lu@intel.com>
+
+	* config/i386/i386.md (*ctz<mode>2_falsedep_1): Don't clear
+	destination if it is used in source.
+	(*clz<mode>2_lzcnt_falsedep_1): Likewise.
+	(*popcount<mode>2_falsedep_1): Likewise.
+
 2014-08-19  H.J. Lu  <hongjiu.lu@intel.com>
 
 	PR other/62168
diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md
index 4749b74294e8..8e74eabb5ab5 100644
--- a/gcc/config/i386/i386.md
+++ b/gcc/config/i386/i386.md
@@ -12269,8 +12269,11 @@
 	    (match_operand:SWI248 1 "nonimmediate_operand")))
      (clobber (reg:CC FLAGS_REG))])])
 
+; False dependency happens when destination is only updated by tzcnt,
+; lzcnt or popcnt.  There is no false dependency when destination is
+; also used in source.
 (define_insn_and_split "*ctz<mode>2_falsedep_1"
-  [(set (match_operand:SWI48 0 "register_operand" "=&r")
+  [(set (match_operand:SWI48 0 "register_operand" "=r")
 	(ctz:SWI48
 	  (match_operand:SWI48 1 "nonimmediate_operand" "rm")))
    (clobber (reg:CC FLAGS_REG))]
@@ -12283,7 +12286,10 @@
 	  (ctz:SWI48 (match_dup 1)))
      (unspec [(match_dup 0)] UNSPEC_INSN_FALSE_DEP)
      (clobber (reg:CC FLAGS_REG))])]
-  "ix86_expand_clear (operands[0]);")
+{
+  if (!reg_mentioned_p (operands[0], operands[1]))
+    ix86_expand_clear (operands[0]);
+})
 
 (define_insn "*ctz<mode>2_falsedep"
   [(set (match_operand:SWI48 0 "register_operand" "=r")
@@ -12363,7 +12369,7 @@
   "TARGET_LZCNT")
 
 (define_insn_and_split "*clz<mode>2_lzcnt_falsedep_1"
-  [(set (match_operand:SWI48 0 "register_operand" "=&r")
+  [(set (match_operand:SWI48 0 "register_operand" "=r")
 	(clz:SWI48
 	  (match_operand:SWI48 1 "nonimmediate_operand" "rm")))
    (clobber (reg:CC FLAGS_REG))]
@@ -12376,7 +12382,10 @@
 	  (clz:SWI48 (match_dup 1)))
      (unspec [(match_dup 0)] UNSPEC_INSN_FALSE_DEP)
      (clobber (reg:CC FLAGS_REG))])]
-  "ix86_expand_clear (operands[0]);")
+{
+  if (!reg_mentioned_p (operands[0], operands[1]))
+    ix86_expand_clear (operands[0]);
+})
 
 (define_insn "*clz<mode>2_lzcnt_falsedep"
   [(set (match_operand:SWI48 0 "register_operand" "=r")
@@ -12683,7 +12692,7 @@
   "TARGET_POPCNT")
 
 (define_insn_and_split "*popcount<mode>2_falsedep_1"
-  [(set (match_operand:SWI48 0 "register_operand" "=&r")
+  [(set (match_operand:SWI48 0 "register_operand" "=r")
 	(popcount:SWI48
 	  (match_operand:SWI48 1 "nonimmediate_operand" "rm")))
    (clobber (reg:CC FLAGS_REG))]
@@ -12696,7 +12705,10 @@
 	  (popcount:SWI48 (match_dup 1)))
      (unspec [(match_dup 0)] UNSPEC_INSN_FALSE_DEP)
      (clobber (reg:CC FLAGS_REG))])]
-  "ix86_expand_clear (operands[0]);")
+{
+  if (!reg_mentioned_p (operands[0], operands[1]))
+    ix86_expand_clear (operands[0]);
+})
 
 (define_insn "*popcount<mode>2_falsedep"
   [(set (match_operand:SWI48 0 "register_operand" "=r")