MIPS/GAS: Clear the ASE_MIPS16E2_MT flag for recalculation

Correct a commit 25499ac7ee ("MIPS16e2: Add MIPS16e2 ASE support") GAS
bug with the handling of the ASE_MIPS16E2_MT combination ASE flag, which
is not correctly calculated as `.set nomips16e2' and `.set nomt'
pseudo-ops are processed.  This leads to code like:

$ cat foo.s
	.set	nomt
	evpe
	.align	4, 0
$ cat bar.s
	.set	nomips16e2
	dvpe
	.align	4, 0
$

to successfully assemble where it should not:

$ as -32 -mips32r3 -mmt -mips16 -mmips16e2 -o foo.o foo.s
$ as -32 -mips32r3 -mmt -mips16 -mmips16e2 -o bar.o bar.s
$ objdump -m mips:16 -d foo.o

foo.o:     file format elf32-tradbigmips

Disassembly of section .text:

00000000 <.text>:
   0:	f027 6700 	evpe
	...

bar.o:     file format elf32-tradbigmips

Disassembly of section .text:

00000000 <.text>:
   0:	f026 6700 	dvpe
	...
$

This happens because ASE_MIPS16E2_MT once set in `mips_set_ase' is never
cleared.  Fix the problem by clearing it there before it is calculated
based on the ASE_MT and ASE_MIPS16E2 flags, making assembly fail as
expected:

$ as -32 -mips32r3 -mmt -mips16 -mmips16e2 -o foo.o foo.s
foo.s: Assembler messages:
foo.s:2: Error: opcode not supported on this processor: mips32r3 (mips32r3) `evpe'
$ as -32 -mips32r3 -mmt -mips16 -mmips16e2 -o bar.o bar.s
bar.s: Assembler messages:
bar.s:2: Error: opcode not supported on this processor: mips32r3 (mips32r3) `dvpe'
$

	gas/
	* config/tc-mips.c (mips_set_ase): Clear the ASE_MIPS16E2_MT
	flag before recalculating.
	* testsuite/gas/mips/mips16e2-mt-err.d: New test.
	* testsuite/gas/mips/mips16e2-mt-err.l: New stderr output.
	* testsuite/gas/mips/mips16e2-mt-err.s: New test source.
	* testsuite/gas/mips/mips.exp: Run the new test.

gas/ChangeLog

@@ -1,3 +1,12 @@
+2017-06-29  Maciej W. Rozycki  <macro@imgtec.com>
+
+	* config/tc-mips.c (mips_set_ase): Clear the ASE_MIPS16E2_MT
+	flag before recalculating.
+	* testsuite/gas/mips/mips16e2-mt-err.d: New test.
+	* testsuite/gas/mips/mips16e2-mt-err.l: New stderr output.
+	* testsuite/gas/mips/mips16e2-mt-err.s: New test source.
+	* testsuite/gas/mips/mips.exp: Run the new test.
+
 2017-06-28  Tamar Christina  <tamar.christina@arm.com>
 
 	* config/tc-aarch64.c (aarch64_reg_parse_32_64): Accept 4B.

gas/config/tc-mips.c

@@ -2130,6 +2130,11 @@ mips_set_ase (const struct mips_ase *ase, struct mips_set_options *opts,
 
   mask = mips_ase_mask (ase->flags);
   opts->ase &= ~mask;
+
+  /* Clear combination ASE flags, which need to be recalculated based on
+     updated regular ASE settings.  */
+  opts->ase &= ~ASE_MIPS16E2_MT;
+
   if (enabled_p)
     opts->ase |= ase->flags;
 

gas/testsuite/gas/mips/mips.exp

@@ -1403,6 +1403,7 @@ if { [istarget mips*-*-vxworks*] } {
 
     run_dump_test "mips16e-jrc"
     run_dump_test "mips16e2-lui"
+    run_dump_test "mips16e2-mt-err"
     run_dump_test "mips16e2-copy"
     run_dump_test "mips16e2-copy-err"
 

gas/testsuite/gas/mips/mips16e2-mt-err.d

@@ -0,0 +1,3 @@
+#name: MIPS16e2 MT ASE instruction errors
+#as: -32 -mips16 -mips32r2 -mmips16e2 -mmt
+#error-output: mips16e2-mt-err.l

gas/testsuite/gas/mips/mips16e2-mt-err.l

@@ -0,0 +1,3 @@
+.*: Assembler messages:
+.*:8: Error: opcode not supported on this processor: mips32r2 \(mips32r2\) `dvpe'
+.*:12: Error: opcode not supported on this processor: mips32r2 \(mips32r2\) `dvpe'

gas/testsuite/gas/mips/mips16e2-mt-err.s

@@ -0,0 +1,14 @@
+# Verify that switching off either `mips16e2' or `mt' causes an assembly
+# error with a MIPS16e2 MT ASE instruction, which requires both at a time.
+
+	.text
+foo:
+	evpe
+	.set	nomips16e2
+	dvpe
+	.set	mips16e2
+	evpe
+	.set	nomt
+	dvpe
+	.set	mt
+	evpe