gas: detect DCTI couples in sparc

Before SPARC V9 the effect of having a delayed branch instruction in the
delay slot of a conditional delayed branch was undefined.

In SPARC V9 DCTI couples are well defined.

However, starting with the UltraSPARC Architecture 2005, DCTI
couples (of all kind) are deprecated and should not be used, as they may
be slow or behave differently to what the programmer expects.

This patch adds a new command line option --dcti-couples-detect to `as',
disabled by default, that makes the assembler to warn the user if an
unpredictable DCTI couple is found.  Tests and documentation are
included.

gas/ChangeLog:

2016-09-14  Jose E. Marchesi  <jose.marchesi@oracle.com>

	* config/tc-sparc.c (md_assemble): Detect and warning on
	unpredictable DCTI couples in certain arches.
	(dcti_couples_detect): New global.
	(md_longopts): Add command line option -dcti-couples-detect.
	(md_show_usage): Document -dcti-couples-detect.
	(md_parse_option): Handle OPTION_DCTI_COUPLES_DETECT.
	* testsuite/gas/sparc/sparc.exp (gas_64_check): Run
	dcti-couples-v8, dcti-couples-v9 and dcti-couples-v9c tests.
	* testsuite/gas/sparc/dcti-couples.s: New file.
	* testsuite/gas/sparc/dcti-couples-v9c.d: Likewise.
	* testsuite/gas/sparc/dcti-couples-v8.d: Likewise.
	* testsuite/gas/sparc/dcti-couples-v9.d: Likewise.
	* testsuite/gas/sparc/dcti-couples-v9c.l: Likewise.
	* testsuite/gas/sparc/dcti-couples-v8.l: Likewise.
	* doc/as.texinfo (Overview): Document --dcti-couples-detect.
	* doc/c-sparc.texi (Sparc-Opts): Likewise.

7 files changed, 45 insertions, 0 deletions

diff --git a/gas/testsuite/gas/sparc/dcti-couples-v8.d b/gas/testsuite/gas/sparc/dcti-couples-v8.d
new file mode 100644
index 0000000..606ce7b
--- /dev/null
+++ b/gas/testsuite/gas/sparc/dcti-couples-v8.d
@@ -0,0 +1,4 @@
+#as: -Av8 --dcti-couples-detect
+#name: dcti couples (v8)
+#source: dcti-couples.s
+#error-output: dcti-couples-v8.l
diff --git a/gas/testsuite/gas/sparc/dcti-couples-v8.l b/gas/testsuite/gas/sparc/dcti-couples-v8.l
new file mode 100644
index 0000000..e3a4e43
--- /dev/null
+++ b/gas/testsuite/gas/sparc/dcti-couples-v8.l
@@ -0,0 +1,2 @@
+.*dcti-couples.s: Assembler messages:
+.*dcti-couples.s:5:.*unpredictable DCTI couple
diff --git a/gas/testsuite/gas/sparc/dcti-couples-v9.d b/gas/testsuite/gas/sparc/dcti-couples-v9.d
new file mode 100644
index 0000000..1641aa2
--- /dev/null
+++ b/gas/testsuite/gas/sparc/dcti-couples-v9.d
@@ -0,0 +1,16 @@
+#as: -Av9 --dcti-couples-detect
+#objdump: -dr
+#name: dcti couples (v9)
+#source: dcti-couples.s
+
+.*: +file format .*sparc.*
+
+Disassembly of section .text:
+
+0+ <.text>:
+   0:	1a 80 00 03 	bcc  0xc
+   4:	10 80 00 02 	b  0xc
+   8:	01 00 00 00 	nop 
+   c:	10 80 00 00 	b  0xc
+  10:	10 bf ff ff 	b  0xc
+  14:	01 00 00 00 	nop 
diff --git a/gas/testsuite/gas/sparc/dcti-couples-v9c.d b/gas/testsuite/gas/sparc/dcti-couples-v9c.d
new file mode 100644
index 0000000..1e1b625
--- /dev/null
+++ b/gas/testsuite/gas/sparc/dcti-couples-v9c.d
@@ -0,0 +1,4 @@
+#as: -Av9c --dcti-couples-detect
+#name: dcti couples (v9c+)
+#source: dcti-couples.s
+#error-output: dcti-couples-v9c.l
diff --git a/gas/testsuite/gas/sparc/dcti-couples-v9c.l b/gas/testsuite/gas/sparc/dcti-couples-v9c.l
new file mode 100644
index 0000000..985daac
--- /dev/null
+++ b/gas/testsuite/gas/sparc/dcti-couples-v9c.l
@@ -0,0 +1,3 @@
+.*dcti-couples.s: Assembler messages:
+.*dcti-couples.s:5:.*unpredictable DCTI couple
+.*dcti-couples.s:12:.*unpredictable DCTI couple
diff --git a/gas/testsuite/gas/sparc/dcti-couples.s b/gas/testsuite/gas/sparc/dcti-couples.s
new file mode 100644
index 0000000..9db550b
--- /dev/null
+++ b/gas/testsuite/gas/sparc/dcti-couples.s
@@ -0,0 +1,13 @@
+        # The execution order of the following DCTI couple is
+        # unpredictable in arches prior to V9, and also in arches
+        # starting with V9C.
+        bcc	1f
+        b	1f
+        nop
+1:
+        # The following DCTI couple is deprecated starting with V9C
+        # (UltraSPARC Architecture 2005) but it is ok in previous
+        # arches.
+	b	1b
+        b	1b
+        nop
diff --git a/gas/testsuite/gas/sparc/sparc.exp b/gas/testsuite/gas/sparc/sparc.exp
index 8cb0904..607f53e 100644
--- a/gas/testsuite/gas/sparc/sparc.exp
+++ b/gas/testsuite/gas/sparc/sparc.exp
@@ -98,6 +98,9 @@ if [istarget sparc*-*-*] {
     run_dump_test "v9branch5"
     run_dump_test "pr19910-1"
     run_list_test "pr19910-2"
+    run_dump_test "dcti-couples-v8"
+    run_dump_test "dcti-couples-v9"
+    run_dump_test "dcti-couples-v9c"
 }
 
 if [istarget sparc-*-vxworks*] {