Index: llvm/trunk/lib/MC/MCParser/AsmParser.cpp
===================================================================
--- llvm/trunk/lib/MC/MCParser/AsmParser.cpp
+++ llvm/trunk/lib/MC/MCParser/AsmParser.cpp
@@ -2067,7 +2067,6 @@
   case AsmToken::AmpAmp:
   case AsmToken::Exclaim:
   case AsmToken::ExclaimEqual:
-  case AsmToken::Percent:
   case AsmToken::Less:
   case AsmToken::LessEqual:
   case AsmToken::LessLess:
@@ -2106,37 +2105,44 @@
   }
 
   unsigned ParenLevel = 0;
-  unsigned AddTokens = 0;
 
   // Darwin doesn't use spaces to delmit arguments.
   AsmLexerSkipSpaceRAII ScopedSkipSpace(Lexer, IsDarwin);
 
+  bool SpaceEaten;
+
   for (;;) {
+    SpaceEaten = false;
     if (Lexer.is(AsmToken::Eof) || Lexer.is(AsmToken::Equal))
       return TokError("unexpected token in macro instantiation");
 
-    if (ParenLevel == 0 && Lexer.is(AsmToken::Comma))
-      break;
+    if (ParenLevel == 0) {
 
-    if (Lexer.is(AsmToken::Space)) {
-      Lex(); // Eat spaces
+      if (Lexer.is(AsmToken::Comma))
+        break;
+
+      if (Lexer.is(AsmToken::Space)) {
+        SpaceEaten = true;
+        Lex(); // Eat spaces
+      }
 
       // Spaces can delimit parameters, but could also be part an expression.
       // If the token after a space is an operator, add the token and the next
       // one into this argument
       if (!IsDarwin) {
         if (isOperator(Lexer.getKind())) {
-          // Check to see whether the token is used as an operator,
-          // or part of an identifier
-          const char *NextChar = getTok().getEndLoc().getPointer();
-          if (*NextChar == ' ')
-            AddTokens = 2;
-        }
+          MA.push_back(getTok());
+          Lex();
 
-        if (!AddTokens && ParenLevel == 0) {
-          break;
+          // Whitespace after an operator can be ignored.
+          if (Lexer.is(AsmToken::Space))
+            Lex();
+
+          continue;
         }
       }
+      if (SpaceEaten)
+        break;
     }
 
     // handleMacroEntry relies on not advancing the lexer here
@@ -2152,8 +2158,6 @@
 
     // Append the token to the current argument list.
     MA.push_back(getTok());
-    if (AddTokens)
-      AddTokens--;
     Lex();
   }
 
Index: llvm/trunk/test/MC/AsmParser/macros-gas.s
===================================================================
--- llvm/trunk/test/MC/AsmParser/macros-gas.s
+++ llvm/trunk/test/MC/AsmParser/macros-gas.s
@@ -39,10 +39,10 @@
 .ascii "\_a \_b \_c"
 .endm
 
-// CHECK: .ascii "1 (23) "
+// CHECK: .ascii "1 (2 3) "
 test3_prime 1, (2 3)
 
-// CHECK: .ascii "1 (23) "
+// CHECK: .ascii "1 (2 3) "
 test3_prime 1 (2 3)
 
 // CHECK: .ascii "1 2 "
Index: llvm/trunk/test/MC/Mips/user-macro-argument-separation.s
===================================================================
--- llvm/trunk/test/MC/Mips/user-macro-argument-separation.s
+++ llvm/trunk/test/MC/Mips/user-macro-argument-separation.s
@@ -0,0 +1,40 @@
+# RUN: llvm-mc %s -triple=mipsel-unknown-linux -show-encoding -mcpu=mips32r2 | \
+# RUN:   FileCheck %s
+# RUN: llvm-mc %s -triple=mipsel-unknown-linux -show-encoding -mcpu=mips32r2 | \
+# RUN:   FileCheck %s
+# RUN: llvm-mc %s -triple=mips-unknown-linux -show-encoding -mcpu=mips32r2 | \
+# RUN:   FileCheck %s
+
+# Check that the IAS expands macro instructions in the same way as GAS
+
+.extern sym
+# imm and rs are deliberately swapped to test whitespace separated arguments.
+.macro EX2 insn, rd, imm, rs
+.ex\@: \insn \rd, \rs, \imm
+.endm
+
+.option pic0
+
+EX2 addiu $2, 1 $3           # CHECK: addiu    $2, $3, 1
+EX2 addiu $2, ~1 $3          # CHECK: addiu    $2, $3, -2
+EX2 addiu $2, ~ 1 $3         # CHECK: addiu    $2, $3, -2
+EX2 addiu $2, 1+1 $3         # CHECK: addiu    $2, $3, 2
+EX2 addiu $2, 1+ 1 $3        # CHECK: addiu    $2, $3, 2
+EX2 addiu $2, 1 +1 $3        # CHECK: addiu    $2, $3, 2
+EX2 addiu $2, 1 + 1 $3       # CHECK: addiu    $2, $3, 2
+EX2 addiu $2, 1+~1 $3        # CHECK: addiu    $2, $3, -1
+EX2 addiu $2, 1+~ 1 $3       # CHECK: addiu    $2, $3, -1
+EX2 addiu $2, 1+ ~1 $3       # CHECK: addiu    $2, $3, -1
+EX2 addiu $2, 1 +~1 $3       # CHECK: addiu    $2, $3, -1
+EX2 addiu $2, 1 +~ 1 $3      # CHECK: addiu    $2, $3, -1
+EX2 addiu $2, 1 + ~1 $3      # CHECK: addiu    $2, $3, -1
+EX2 addiu $2, 1 + ~ 1 $3     # CHECK: addiu    $2, $3, -1
+EX2 addiu $2, 1+(1) $3       # CHECK: addiu    $2, $3, 2
+EX2 addiu $2, 1 +(1) $3      # CHECK: addiu    $2, $3, 2
+EX2 addiu $2, 1+ (1) $3      # CHECK: addiu    $2, $3, 2
+EX2 addiu $2, 1 + (1) $3     # CHECK: addiu    $2, $3, 2
+EX2 addiu $2, 1+(1)+1 $3     # CHECK: addiu    $2, $3, 3
+EX2 addiu $2, 1 +(1)+1 $3    # CHECK: addiu    $2, $3, 3
+EX2 addiu $2, 1+ (1)+1 $3    # CHECK: addiu    $2, $3, 3
+EX2 addiu $2, 1 + (1)+1 $3   # CHECK: addiu    $2, $3, 3
+nop                          # CHECK: nop