MIPS/GAS: Implement microMIPS branch/jump compaction

Convert microMIPS branches and jumps whose delay slot would be filled by
a generated NOP instruction to the corresponding compact form where one
exists, in a manner similar to MIPS16 JR->JRC and JALR->JALRC swap.

Do so even where the transformation switches from a 16-bit to a 32-bit
branch encoding for no benefit in code size reduction, as this is still
advantageous.  This is because a branch/NOP pair takes 2 pipeline slots
or a 2-cycle completion latency except in superscalar implementations.
Whereas a compact branch may or may not stall on its target fetch, so it
will at most have a 2-cycle completion latency and may have only 1 even
in scalar implementations, and in superscalar implementations it is
expected to have no worse latency as a branch/NOP pair has.  Also it
won't stall and therefore take the extra latency cycle in the not-taken
case.

Technically this is the same as MIPS16 compaction: for the qualifying
instruction encodings the APPEND_ADD_COMPACT machine code generation
method is selected where APPEND_ADD_WITH_NOP otherwise would and tells
the code generator in `append_insn' to convert the regular form of an
instruction to its corresponding compact form.  For this the opcode is
tweaked as necessary and the microMIPS opcode table is scanned for the
matching updated instruction.  A non-$0 `rt' operand to BEQ and BNE
instructions is moved to the `rs' operand field of BEQZC and BNEZC
encodings as required.

Unlike with MIPS16 compaction however we need to handle out-of-distance
branch relaxation as well.  We do this by deferring the generation of
any delay-slot NOP required to relaxation made in `md_convert_frag', by
converting the APPEND_ADD_WITH_NOP machine code generation to APPEND_ADD
where a relaxed instruction is recorded.  Relaxation then, depending on
actual code produced, chooses between either using a compact branch or
jump encoding and emitting the NOP outstanding if no compact encoding is
possible.

For code simplicity's sake the relaxation pass is retained even if the
principle of preferring a compact encoding to a 16-bit branch/NOP pair
means, in the absence of out-of-range branch relaxation, that a single
compact branch machine code instruction will eventually be produced from
a given assembly source instruction.

	gas/
	* config/tc-mips.c (RELAX_MICROMIPS_ENCODE): Add `nods' flag.
	(RELAX_MICROMIPS_RELAX32, RELAX_MICROMIPS_TOOFAR16)
	(RELAX_MICROMIPS_MARK_TOOFAR16, RELAX_MICROMIPS_CLEAR_TOOFAR16)
	(RELAX_MICROMIPS_TOOFAR32, RELAX_MICROMIPS_MARK_TOOFAR32)
	(RELAX_MICROMIPS_CLEAR_TOOFAR32): Shift bits.
	(get_append_method): Also return APPEND_ADD_COMPACT for
	microMIPS instructions.
	(find_altered_mips16_opcode): Exclude macros from matching.
	Factor code out...
	(find_altered_opcode): ... to this new function.
	(find_altered_micromips_opcode): New function.
	(frag_branch_delay_slot_size): Likewise.
	(append_insn): Handle microMIPS branch/jump compaction.
	(macro_start): Likewise.
	(relaxed_micromips_32bit_branch_length): Likewise.
	(md_convert_frag): Likewise.
	* testsuite/gas/mips/micromips.s: Add conditional explicit NOPs
	for delay slot filling.
	* testsuite/gas/mips/micromips-b16.s: Add explicit NOPs for
	delay slot filling.
	* testsuite/gas/mips/micromips-size-1.s: Likewise.
	* testsuite/gas/mips/micromips.l: Adjust line numbers.
	* testsuite/gas/mips/micromips-warn.l: Likewise.
	* testsuite/gas/mips/micromips-size-1.l: Likewise.
	* testsuite/gas/mips/micromips.d: Adjust padding.
	* testsuite/gas/mips/micromips-trap.d: Likewise.
	* testsuite/gas/mips/micromips-insn32.d: Likewise.
	* testsuite/gas/mips/micromips-noinsn32.d: Likewise.
	* testsuite/gas/mips/micromips@beq.d: Update patterns for
	branch/jump compaction.
	* testsuite/gas/mips/micromips@bge.d: Likewise.
	* testsuite/gas/mips/micromips@bgeu.d: Likewise.
	* testsuite/gas/mips/micromips@blt.d: Likewise.
	* testsuite/gas/mips/micromips@bltu.d: Likewise.
	* testsuite/gas/mips/micromips@branch-misc-4.d: Likewise.
	* testsuite/gas/mips/micromips@branch-misc-4-64.d: Likewise.
	* testsuite/gas/mips/micromips@branch-misc-5.d: Likewise.
	* testsuite/gas/mips/micromips@branch-misc-5pic.d: Likewise.
	* testsuite/gas/mips/micromips@branch-misc-5-64.d: Likewise.
	* testsuite/gas/mips/micromips@branch-misc-5pic-64.d: Likewise.
	* testsuite/gas/mips/micromips@jal-svr4pic-local.d: Likewise.
	* testsuite/gas/mips/micromips@jal-svr4pic-local-n32.d:
	Likewise.
	* testsuite/gas/mips/micromips@jal-svr4pic-local-n64.d:
	Likewise.
	* testsuite/gas/mips/micromips@loc-swap.d: Likewise.
	* testsuite/gas/mips/micromips@loc-swap-dis.d: Likewise.
	* testsuite/gas/mips/micromips@relax.d: Likewise.
	* testsuite/gas/mips/micromips@relax-at.d: Likewise.
	* testsuite/gas/mips/micromips@relax-swap3.d: Likewise.
	* testsuite/gas/mips/branch-extern-2.d: Likewise.
	* testsuite/gas/mips/branch-extern-4.d: Likewise.
	* testsuite/gas/mips/branch-section-2.d: Likewise.
	* testsuite/gas/mips/branch-section-4.d: Likewise.
	* testsuite/gas/mips/branch-weak-2.d: Likewise.
	* testsuite/gas/mips/branch-weak-5.d: Likewise.
	* testsuite/gas/mips/micromips-branch-absolute.d: Likewise.
	* testsuite/gas/mips/micromips-branch-absolute-n32.d: Likewise.
	* testsuite/gas/mips/micromips-branch-absolute-n64.d: Likewise.
	* testsuite/gas/mips/micromips-branch-absolute-addend.d:
	Likewise.
	* testsuite/gas/mips/micromips-branch-absolute-addend-n32.d:
	Likewise.
	* testsuite/gas/mips/micromips-branch-absolute-addend-n64.d:
	Likewise.
	* testsuite/gas/mips/micromips-compact.d: New test.
	* testsuite/gas/mips/mips.exp: Run the new test.

	ld/
	* testsuite/ld-mips-elf/micromips-branch-absolute.d: Update
	patterns for branch compaction.
	* testsuite/ld-mips-elf/micromips-branch-absolute-addend.d:
	Likewise.

	opcodes/
	* micromips-opc.c (micromips_opcodes): Reorder "bc" next to "b",
	"beqzc" next to "beq", "bnezc" next to "bne" and "jrc" next to
	"j".

3 files changed, 17 insertions, 16 deletions

diff --git a/ld/ChangeLog b/ld/ChangeLog
index 8c4e5d4..99bb6df 100644
--- a/ld/ChangeLog
+++ b/ld/ChangeLog
@@ -1,3 +1,10 @@
+2016-07-27  Maciej W. Rozycki  <macro@imgtec.com>
+
+	* testsuite/ld-mips-elf/micromips-branch-absolute.d: Update
+	patterns for branch compaction.
+	* testsuite/ld-mips-elf/micromips-branch-absolute-addend.d:
+	Likewise.
+
 2016-07-27  Nick Clifton  <nickc@redhat.com>
 
 	* testsuite/ld-gc/personality.d: Use "target cfi" to restrict the
diff --git a/ld/testsuite/ld-mips-elf/micromips-branch-absolute-addend.d b/ld/testsuite/ld-mips-elf/micromips-branch-absolute-addend.d
index ec78ff9..fc3bd03 100644
--- a/ld/testsuite/ld-mips-elf/micromips-branch-absolute-addend.d
+++ b/ld/testsuite/ld-mips-elf/micromips-branch-absolute-addend.d
@@ -8,15 +8,12 @@
 
 Disassembly of section \.text:
 	\.\.\.
-[0-9a-f]+ <[^>]*> 9400 2c54 	b	0*123468ac <bar\+0x1233>
-[0-9a-f]+ <[^>]*> 0c00      	nop
-[0-9a-f]+ <[^>]*> 4060 2c51 	bal	0*123468ac <bar\+0x1233>
+[0-9a-f]+ <[^>]*> 40e0 2c54 	bc	0*123468ac <bar\+0x1233>
+[0-9a-f]+ <[^>]*> 4060 2c52 	bal	0*123468ac <bar\+0x1233>
 [0-9a-f]+ <[^>]*> 0000 0000 	nop
-[0-9a-f]+ <[^>]*> 4020 2c4d 	bltzal	zero,0*123468ac <bar\+0x1233>
+[0-9a-f]+ <[^>]*> 4020 2c4e 	bltzal	zero,0*123468ac <bar\+0x1233>
 [0-9a-f]+ <[^>]*> 0000 0000 	nop
-[0-9a-f]+ <[^>]*> 9402 2c49 	beqz	v0,0*123468ac <bar\+0x1233>
-[0-9a-f]+ <[^>]*> 0c00      	nop
-[0-9a-f]+ <[^>]*> b402 2c46 	bnez	v0,0*123468ac <bar\+0x1233>
-[0-9a-f]+ <[^>]*> 0c00      	nop
+[0-9a-f]+ <[^>]*> 40e2 2c4a 	beqzc	v0,0*123468ac <bar\+0x1233>
+[0-9a-f]+ <[^>]*> 40a2 2c48 	bnezc	v0,0*123468ac <bar\+0x1233>
 [0-9a-f]+ <[^>]*> 0c00      	nop
 	\.\.\.
diff --git a/ld/testsuite/ld-mips-elf/micromips-branch-absolute.d b/ld/testsuite/ld-mips-elf/micromips-branch-absolute.d
index f07ad1b..ad44f5a 100644
--- a/ld/testsuite/ld-mips-elf/micromips-branch-absolute.d
+++ b/ld/testsuite/ld-mips-elf/micromips-branch-absolute.d
@@ -8,15 +8,12 @@
 
 Disassembly of section \.text:
 	\.\.\.
-[0-9a-f]+ <[^>]*> 9400 0118 	b	0+001234 <foo\+0x234>
-[0-9a-f]+ <[^>]*> 0c00      	nop
-[0-9a-f]+ <[^>]*> 4060 0115 	bal	0+001234 <foo\+0x234>
+[0-9a-f]+ <[^>]*> 40e0 0118 	bc	0+001234 <foo\+0x234>
+[0-9a-f]+ <[^>]*> 4060 0116 	bal	0+001234 <foo\+0x234>
 [0-9a-f]+ <[^>]*> 0000 0000 	nop
-[0-9a-f]+ <[^>]*> 4020 0111 	bltzal	zero,0+001234 <foo\+0x234>
+[0-9a-f]+ <[^>]*> 4020 0112 	bltzal	zero,0+001234 <foo\+0x234>
 [0-9a-f]+ <[^>]*> 0000 0000 	nop
-[0-9a-f]+ <[^>]*> 9402 010d 	beqz	v0,0+001234 <foo\+0x234>
-[0-9a-f]+ <[^>]*> 0c00      	nop
-[0-9a-f]+ <[^>]*> b402 010a 	bnez	v0,0+001234 <foo\+0x234>
-[0-9a-f]+ <[^>]*> 0c00      	nop
+[0-9a-f]+ <[^>]*> 40e2 010e 	beqzc	v0,0+001234 <foo\+0x234>
+[0-9a-f]+ <[^>]*> 40a2 010c 	bnezc	v0,0+001234 <foo\+0x234>
 [0-9a-f]+ <[^>]*> 0c00      	nop
 	\.\.\.