[ARM] Allow automatically deducing the thumb instruction size for .inst

This matches GAS, that allows unsuffixed .inst for thumb.

Differential Revision: https://reviews.llvm.org/D49937

llvm-svn: 338357

1 files changed, 14 insertions, 3 deletions

diff --git a/llvm/lib/Target/ARM/AsmParser/ARMAsmParser.cpp b/llvm/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
index ed706ab7a29..a5fbbbf26be 100644
--- a/llvm/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
+++ b/llvm/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
@@ -10012,8 +10012,8 @@ bool ARMAsmParser::parseDirectiveInst(SMLoc Loc, char Suffix) {
     case 'w':
       break;
     default:
-      return Error(Loc, "cannot determine Thumb instruction size, "
-                        "use inst.n/inst.w instead");
+      Width = 0;
+      break;
     }
   } else {
     if (Suffix)
@@ -10029,6 +10029,7 @@ bool ARMAsmParser::parseDirectiveInst(SMLoc Loc, char Suffix) {
       return Error(Loc, "expected constant expression");
     }
 
+    char CurSuffix = Suffix;
     switch (Width) {
     case 2:
       if (Value->getValue() > 0xffff)
@@ -10039,11 +10040,21 @@ bool ARMAsmParser::parseDirectiveInst(SMLoc Loc, char Suffix) {
         return Error(Loc, StringRef(Suffix ? "inst.w" : "inst") +
                               " operand is too big");
       break;
+    case 0:
+      // Thumb mode, no width indicated. Guess from the opcode, if possible.
+      if (Value->getValue() < 0xe800)
+        CurSuffix = 'n';
+      else if (Value->getValue() >= 0xe8000000)
+        CurSuffix = 'w';
+      else
+        return Error(Loc, "cannot determine Thumb instruction size, "
+                          "use inst.n/inst.w instead");
+      break;
     default:
       llvm_unreachable("only supported widths are 2 and 4");
     }
 
-    getTargetStreamer().emitInst(Value->getValue(), Suffix);
+    getTargetStreamer().emitInst(Value->getValue(), CurSuffix);
     return false;
   };