[PATCH] Fix for PR20104. Enable GAS compliant coprocessor register name.

[Andrey Kuharev]

Added parsing for parameter names starting with "cr"

Additional compliant GAS names for coprocessor register name 
are enabled for all instruction with parameter MCK_CoprocReg:
LDC,LDC2,STC,STC2,CDP,CDP2,MCR,MCR2,MCRR,MCRR2,MRC,MRC2,MRRC,MRRC2
...

http://reviews.llvm.org/D4254

Files:
  lib/Target/ARM/AsmParser/ARMAsmParser.cpp
  test/MC/ARM/gas-compl-copr-reg.s

Index: lib/Target/ARM/AsmParser/ARMAsmParser.cpp
===================================================================
--- lib/Target/ARM/AsmParser/ARMAsmParser.cpp
+++ lib/Target/ARM/AsmParser/ARMAsmParser.cpp
@@ -3083,15 +3083,19 @@
 
 /// MatchCoprocessorOperandName - Try to parse an coprocessor related
 /// instruction with a symbolic operand name. Example: "p1", "p7", "c3",
-/// "c5", ...
+/// "c5", cr0, cr5 ...
 static int MatchCoprocessorOperandName(StringRef Name, char CoprocOp) {
   // Use the same layout as the tablegen'erated register name matcher. Ugly,
   // but efficient.
+  if (Name.size() < 2 || Name[0] != CoprocOp)
+    return -1;
+
+  if (Name.startswith("cr")) // For gas compatibility
+    Name = Name.drop_front();
+
   switch (Name.size()) {
   default: return -1;
   case 2:
-    if (Name[0] != CoprocOp)
-      return -1;
     switch (Name[1]) {
     default:  return -1;
     case '0': return 0;
@@ -3106,7 +3110,7 @@
     case '9': return 9;
     }
   case 3:
-    if (Name[0] != CoprocOp || Name[1] != '1')
+    if (Name[1] != '1')
       return -1;
     switch (Name[2]) {
     default:  return -1;
Index: test/MC/ARM/gas-compl-copr-reg.s
===================================================================
--- test/MC/ARM/gas-compl-copr-reg.s
+++ test/MC/ARM/gas-compl-copr-reg.s
@@ -0,0 +1,7 @@
+@ RUN: llvm-mc -triple=armv7-linux-gnueabi -show-encoding < %s | FileCheck %s
+
+@ CHECK: ldc	p12, c4, [r0, #4]       @ encoding: [0x01,0x4c,0x90,0xed]
+@ CHECK: stc	p14, c6, [r2, #-224]    @ encoding: [0x38,0x6e,0x02,0xed]
+
+        ldc p12, cr4, [r0, #4]
+        stc p14, cr6, [r2, #-224]
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