[PATCH] ARM: fix IT decoding

[Amaury de la Vieuville]

Hi rengolin, t.p.northover,

mask == 0 -> UNPRED

http://llvm-reviews.chandlerc.com/D1022

Files:
  lib/Target/ARM/Disassembler/ARMDisassembler.cpp
  test/MC/Disassembler/ARM/invalid-IT-thumb.txt

Index: lib/Target/ARM/Disassembler/ARMDisassembler.cpp
===================================================================
--- lib/Target/ARM/Disassembler/ARMDisassembler.cpp
+++ lib/Target/ARM/Disassembler/ARMDisassembler.cpp
@@ -4588,10 +4588,8 @@
     S = MCDisassembler::SoftFail;
   }
 
-  if (mask == 0x0) {
-    mask |= 0x8;
-    S = MCDisassembler::SoftFail;
-  }
+  if (mask == 0x0)
+    return MCDisassembler::Fail;
 
   Inst.addOperand(MCOperand::CreateImm(pred));
   Inst.addOperand(MCOperand::CreateImm(mask));
Index: test/MC/Disassembler/ARM/invalid-IT-thumb.txt
===================================================================
--- test/MC/Disassembler/ARM/invalid-IT-thumb.txt
+++ test/MC/Disassembler/ARM/invalid-IT-thumb.txt
@@ -1,3 +1,7 @@
-# RUN: llvm-mc --disassemble %s -triple=thumbv7-unknown-unknown 2>&1 | grep "potentially undefined instruction encoding"
+# CHECK-UNPRED: potentially undefined instruction encoding
+# CHECK-UNDEF: invalid instruction encoding
 
-0xff 0xbf 0x6b 0x80 0x00 0x75
+# RUN: echo "0xff 0xbf 0x6b 0x80 0x00 0x75" | llvm-mc -disassemble -triple thumbv7 2>&1 | FileCheck %s --check-prefix=CHECK-UNPRED
+
+# mask = 0
+# RUN: echo "0x50 0xbf 0x00 0x00" | llvm-mc -disassemble -triple thumbv7 2>&1 | FileCheck %s --check-prefix=CHECK-UNDEF
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