[Patch AArch64] Turn lr, fp, ip0 and ip1 into proper aliases

We got a report from the linux-arm-kernel folks about getting spurious
warnings when building the kernel with binutils 2.29. See
https://www.spinics.net/lists/arm-kernel/msg599929.html

which boils down to this testcase.

$> cat /tmp/tst.s
    lr .req x30
    /tmp/tst.s: Assembler messages:
    /tmp/tst.s:1: Warning: ignoring attempt to redefine built-in register 'lr'

Instead let's treat this as a proper alias at startup time thus
avoiding the problem and treating these as proper aliases
rather than new registers. This means that attempts to redefine
the alias with the same "name" will provoke no warning and attempts
to redefine the alias to something else will provoke the above mentioned
warning.

Tested make check-gas and no regressions.

Ok to apply to trunk (and backport to 2.29 branch)?

Regards
Ramana

gas/ChangeLog

@@ -1,3 +1,13 @@
+2017-08-15  Ramana Radhakrishnan  <ramana.radhakrishnan@arm.com>
+
+	* config/tc-aarch64.c (REGDEF_ALIAS): Define
+	(reg_names): Update for ip0, ip1, fp, lr to use REGDEF_ALIAS
+	* doc/c-aarch64.texi: Update documentation on .req.
+	* testsuite/gas/diagnostic.s: Update
+	* testsuite/gas/diagnostic.l: Likewise
+	* testsuite/gas/register_aliases.s: New file.
+	* testsuite/gas/register_aliases.d: New file.
+
 2017-08-11  H.J. Lu  <hongjiu.lu@intel.com>
 
 	PR gas/21667

gas/config/tc-aarch64.c

@@ -6772,6 +6772,7 @@ aarch64_canonicalize_symbol_name (char *name)
    also have mixed-case names.	*/
 
 #define REGDEF(s,n,t) { #s, n, REG_TYPE_##t, TRUE }
+#define REGDEF_ALIAS(s, n, t) { #s, n, REG_TYPE_##t, FALSE}
 #define REGNUM(p,n,t) REGDEF(p##n, n, t)
 #define REGSET16(p,t) \
   REGNUM(p, 0,t), REGNUM(p, 1,t), REGNUM(p, 2,t), REGNUM(p, 3,t), \
@@ -6793,17 +6794,16 @@ static const reg_entry reg_names[] = {
   REGSET31 (x, R_64), REGSET31 (X, R_64),
   REGSET31 (w, R_32), REGSET31 (W, R_32),
 
+  REGDEF_ALIAS (ip0, 16, R_64), REGDEF_ALIAS (IP0, 16, R_64),
+  REGDEF_ALIAS (ip1, 17, R_64), REGDEF_ALIAS (IP1, 16, R_64),
+  REGDEF_ALIAS (fp, 29, R_64), REGDEF_ALIAS (FP, 29, R_64),
+  REGDEF_ALIAS (lr, 30, R_64), REGDEF_ALIAS (LR, 30, R_64),
   REGDEF (wsp, 31, SP_32), REGDEF (WSP, 31, SP_32),
   REGDEF (sp, 31, SP_64), REGDEF (SP, 31, SP_64),
 
   REGDEF (wzr, 31, Z_32), REGDEF (WZR, 31, Z_32),
   REGDEF (xzr, 31, Z_64), REGDEF (XZR, 31, Z_64),
 
-  REGDEF (ip0, 16, R_64), REGDEF (IP0, 16, R_64),
-  REGDEF (ip1, 17, R_64), REGDEF (IP1, 17, R_64),
-  REGDEF (fp, 29, R_64), REGDEF (FP, 29, R_64),
-  REGDEF (lr, 30, R_64), REGDEF (LR, 30, R_64),
-
   /* Floating-point single precision registers.  */
   REGSET (s, FP_S), REGSET (S, FP_S),
 
@@ -6830,6 +6830,7 @@ static const reg_entry reg_names[] = {
 };
 
 #undef REGDEF
+#undef REGDEF_ALIAS
 #undef REGNUM
 #undef REGSET16
 #undef REGSET31

gas/doc/c-aarch64.texi

@@ -363,6 +363,9 @@ example:
         foo .req w0
 @end smallexample
 
+ip0, ip1, lr and fp are automatically defined to
+alias to X16, X17, X30 and X29 respectively.
+
 @c SSSSSSSSSSSSSSSSSSSSSSSSSS
 
 @c TTTTTTTTTTTTTTTTTTTTTTTTTT

gas/testsuite/gas/aarch64/diagnostic.l

@@ -172,3 +172,7 @@
 [^:]*:295: Error: invalid use of 'MUL' at operand 4 -- `orr x0,x0,#0xff,mul#1'
 [^:]*:296: Error: invalid use of 'MUL' at operand 4 -- `orr x0,x0,#0xfe,mul#255'
 [^:]*:297: Error: invalid use of 'MUL' at operand 4 -- `orr x0,x0,#0xfc,mul#256'
+[^:]*:299: Warning: ignoring redefinition of register alias 'ip0'
+[^:]*:300: Warning: ignoring redefinition of register alias 'ip1'
+[^:]*:301: Warning: ignoring redefinition of register alias 'lr'
+[^:]*:302: Warning: ignoring redefinition of register alias 'fp'

gas/testsuite/gas/aarch64/diagnostic.s

@@ -295,3 +295,8 @@
 	orr	x0, x0, #0xff, mul #1
 	orr	x0, x0, #0xfe, mul #255
 	orr	x0, x0, #0xfc, mul #256
+
+	ip0 	.req 	x0
+	ip1	.req 	x1
+	lr	.req 	x2
+	fp	.req 	x3

gas/testsuite/gas/aarch64/register_aliases.d

@@ -0,0 +1,10 @@
+#objdump: -dr
+
+.*:     file format .*
+
+Disassembly of section \.text:
+
+0+ <.*>:
+   0:	8b1e0210 	add	x16, x16, x30
+   4:	f90003b0 	str	x16, \[x29\]
+   8:	f94003b1 	ldr	x17, \[x29\]

gas/testsuite/gas/aarch64/register_aliases.s

@@ -0,0 +1,9 @@
+	# test register aliases.
+	lr	.req 	x30
+	fp 	.req 	x29
+	ip0	.req 	x16
+	ip1	.req 	x17
+	add	ip0, ip0, lr
+	str 	ip0, [fp]
+	ldr	ip1, [fp]
+