Fixed the arm disassembly of invalid BFI instructions to not build a …

…bad MCInst

which would then cause an assert when printed.  rdar://11437956


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@168960 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/ARM/Disassembler/ARMDisassembler.cpp

@@ -1281,7 +1281,13 @@ static DecodeStatus DecodeBitfieldMaskOperand(MCInst &Inst, unsigned Val,
   unsigned lsb = fieldFromInstruction(Val, 0, 5);
 
   DecodeStatus S = MCDisassembler::Success;
-  if (lsb > msb) Check(S, MCDisassembler::SoftFail);
+  if (lsb > msb) {
+    Check(S, MCDisassembler::SoftFail);
+    // The check above will cause the warning for the "potentially undefined
+    // instruction encoding" but we can't build a bad MCOperand value here
+    // with a lsb > msb or else printing the MCInst will cause a crash.
+    lsb = msb;
+  }
 
   uint32_t msb_mask = 0xFFFFFFFF;
   if (msb != 31) msb_mask = (1U << (msb+1)) - 1;

test/MC/Disassembler/ARM/unpredictable-BFI.txt

@@ -0,0 +1,11 @@
+# RUN: llvm-mc --disassemble %s -triple=arm-apple-darwin9 2>&1 | FileCheck %s
+
+# rdar://11437956
+
+# CHECK: warning: invalid instruction encoding
+# CHECK: 0x90 0x00 0xc0 0xe7
+0x90 0x00 0xc0 0xe7
+
+# CHECK: warning: invalid instruction encoding
+# CHECK: 0x90 0x01 0xc0 0xe7
+0x90 0x01 0xc0 0xe7