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

[Andrey Kuharev]

Reduced

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
@@ -3082,17 +3082,25 @@
 }
 
 /// MatchCoprocessorOperandName - Try to parse an coprocessor related
-/// instruction with a symbolic operand name. Example: "p1", "p7", "c3",
-/// "c5", ...
+/// instruction with a symbolic operand name. 
+/// We accept "crN" syntax for GAS compatibility.
+/// <operand-name> ::= <prefix><number> 
+/// If CoprocOp is 'c', then:
+///   <prefix> ::= c | cr
+/// If CoprocOp is 'p', then :
+///   <prefix> ::= p
+/// <number> ::= integer in range [0, 15]
 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;
+  Name = (Name[1] == 'r') ? Name.drop_front(2) : Name.drop_front();
+
   switch (Name.size()) {
   default: return -1;
-  case 2:
-    if (Name[0] != CoprocOp)
-      return -1;
-    switch (Name[1]) {
+  case 1:
+    switch (Name[0]) {
     default:  return -1;
     case '0': return 0;
     case '1': return 1;
@@ -3105,10 +3113,10 @@
     case '8': return 8;
     case '9': return 9;
     }
-  case 3:
-    if (Name[0] != CoprocOp || Name[1] != '1')
+  case 2:
+    if (Name[0] != '1')
       return -1;
-    switch (Name[2]) {
+    switch (Name[1]) {
     default:  return -1;
     // p10 and p11 are invalid for coproc instructions (reserved for FP/NEON)
     case '0': return CoprocOp == 'p'? -1: 10;
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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