Fix ARM's b.w instruction for thumb 2 and the encoding T4. The branch target

is 24 bits not 20 and the decoding needed to correctly handle converting the
J1 and J2 bits to their I1 and I2 values to reconstruct the displacement. 


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@166982 91177308-0d34-0410-b5e6-96231b3b80d8

4 files changed, 38 insertions, 11 deletions

diff --git a/lib/Target/ARM/ARMInstrThumb2.td b/lib/Target/ARM/ARMInstrThumb2.td
index 1684339d6f..94bc23eb77 100644
--- a/lib/Target/ARM/ARMInstrThumb2.td
+++ b/lib/Target/ARM/ARMInstrThumb2.td
@@ -3245,11 +3245,11 @@ def t2B   : T2I<(outs), (ins uncondbrtarget:$target), IIC_Br,
   let Inst{15-14} = 0b10;
   let Inst{12} = 1;
 
-  bits<20> target;
+  bits<24> target;
   let Inst{26} = target{19};
   let Inst{11} = target{18};
   let Inst{13} = target{17};
-  let Inst{21-16} = target{16-11};
+  let Inst{25-16} = target{20-11};
   let Inst{10-0} = target{10-0};
   let DecoderMethod = "DecodeT2BInstruction";
 }
diff --git a/lib/Target/ARM/Disassembler/ARMDisassembler.cpp b/lib/Target/ARM/Disassembler/ARMDisassembler.cpp
index d2b1cc37f2..f00142de50 100644
--- a/lib/Target/ARM/Disassembler/ARMDisassembler.cpp
+++ b/lib/Target/ARM/Disassembler/ARMDisassembler.cpp
@@ -2095,16 +2095,28 @@ static DecodeStatus DecodeAddrMode7Operand(MCInst &Inst, unsigned Val,
 static DecodeStatus
 DecodeT2BInstruction(MCInst &Inst, unsigned Insn,
                      uint64_t Address, const void *Decoder) {
-  DecodeStatus S = MCDisassembler::Success;
-  unsigned imm = (fieldFromInstruction(Insn, 0, 11) << 0) |
-                 (fieldFromInstruction(Insn, 11, 1) << 18) |
-                 (fieldFromInstruction(Insn, 13, 1) << 17) |
-                 (fieldFromInstruction(Insn, 16, 6) << 11) |
-                 (fieldFromInstruction(Insn, 26, 1) << 19);
-  if (!tryAddingSymbolicOperand(Address, Address + SignExtend32<20>(imm<<1) + 4,
+  DecodeStatus Status = MCDisassembler::Success;
+
+  // Note the J1 and J2 values are from the encoded instruction.  So here
+  // change them to I1 and I2 values via as documented:
+  // I1 = NOT(J1 EOR S);
+  // I2 = NOT(J2 EOR S);
+  // and build the imm32 with one trailing zero as documented:
+  // imm32 = SignExtend(S:I1:I2:imm10:imm11:'0', 32);
+  unsigned S = fieldFromInstruction(Insn, 26, 1);
+  unsigned J1 = fieldFromInstruction(Insn, 13, 1);
+  unsigned J2 = fieldFromInstruction(Insn, 11, 1);
+  unsigned I1 = !(J1 ^ S);
+  unsigned I2 = !(J2 ^ S);
+  unsigned imm10 = fieldFromInstruction(Insn, 16, 10);
+  unsigned imm11 = fieldFromInstruction(Insn, 0, 11);
+  unsigned tmp = (S << 23) | (I1 << 22) | (I2 << 21) | (imm10 << 11) | imm11;
+  int imm32 = SignExtend32<24>(tmp << 1);
+  if (!tryAddingSymbolicOperand(Address, Address + imm32 + 4,
                                 true, 4, Inst, Decoder))
-    Inst.addOperand(MCOperand::CreateImm(SignExtend32<20>(imm << 1)));
-  return S;
+    Inst.addOperand(MCOperand::CreateImm(imm32));
+
+  return Status;
 }
 
 static DecodeStatus
diff --git a/test/MC/ARM/thumb2-b.w-encodingT4.s b/test/MC/ARM/thumb2-b.w-encodingT4.s
new file mode 100644
index 0000000000..be77b06267
--- /dev/null
+++ b/test/MC/ARM/thumb2-b.w-encodingT4.s
@@ -0,0 +1,12 @@
+@ RUN: llvm-mc -triple=thumbv7-apple-darwin -mcpu=cortex-a8 -show-encoding < %s | FileCheck %s
+  .syntax unified
+  .globl _func
+.thumb_func _foo
+.space 0x37c6
+_foo:
+@------------------------------------------------------------------------------
+@ B (thumb2 b.w encoding T4) rdar://12585795
+@------------------------------------------------------------------------------
+        b.w   0x3680c
+
+@ CHECK: b.w	#223244                    @ encoding: [0x6d,0xf0,0x0c,0xb0]
diff --git a/test/MC/Disassembler/ARM/thumb2.txt b/test/MC/Disassembler/ARM/thumb2.txt
index 42ebe58207..45dace3b09 100644
--- a/test/MC/Disassembler/ARM/thumb2.txt
+++ b/test/MC/Disassembler/ARM/thumb2.txt
@@ -169,6 +169,9 @@
 
 0x13 0xf5 0xce 0xa9
 
+# CHECK: b.w   #208962
+
+0x33 0xf0 0x21 0xb8 # rdar://12585795
 
 #------------------------------------------------------------------------------
 # BFC