From ad6267596c510660a93889a53319e9f051cab39a Mon Sep 17 00:00:00 2001
From: Michael Meissner <meissner@gcc.gnu.org>
Date: Fri, 25 Nov 1994 23:57:41 +0000
Subject: [PATCH] Add comment on ffs to say why optimizing it further is a bad
 idea.

From-SVN: r8564
---
 gcc/config/i386/i386.md | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md
index a4cfff591f5..5dfa166d3be 100644
--- a/gcc/config/i386/i386.md
+++ b/gcc/config/i386/i386.md
@@ -5439,6 +5439,10 @@
   ""
   "operands[2] = gen_reg_rtx (SImode);")
 
+;; Note, you cannot optimize away the branch following the bsfl by assuming
+;; that the destination is not modified if the input is 0, since not all
+;; x86 implementations do this.
+
 (define_insn ""
   [(set (match_operand:SI 0 "general_operand" "=&r")
 	(plus:SI (ffs:SI (match_operand:SI 1 "general_operand" "rm"))
@@ -5453,7 +5457,6 @@
   xops[0] = operands[0];
   xops[1] = operands[1];
   xops[2] = constm1_rtx;
-  /* Can there be a way to avoid the jump here?  */
   output_asm_insn (AS2 (bsf%L0,%1,%0), xops);
 #ifdef LOCAL_LABEL_PREFIX
   sprintf (buffer, \"jnz %sLFFSSI%d\",
-- 
2.30.2