Added the B9.3.19 SUBS PC, LR, #imm (Thumb2) system instruction.

While the .td entry is nice and all, it takes a pretty gross hack in
ARMAsmParser::ParseInstruction() because of handling of other "subs"
instructions to get it to match.  Ran it by Jim Grosbach and he said it was
about what he expected to make this work given the existing code.

rdar://14214063

llvm-svn: 187530

llvm/lib/Target/ARM/ARMInstrThumb2.td

@@ -3599,6 +3599,16 @@ def t2RFEIA  : T2RFE<0b111010011001,
                    (outs), (ins GPR:$Rn), NoItinerary, "rfeia", "\t$Rn",
                    [/* For disassembly only; pattern left blank */]>;
 
+// B9.3.19 SUBS PC, LR, #imm (Thumb2) system instruction.
+let Defs = [PC], Uses = [LR] in
+def t2SUBS_PC_LR : T2I <(outs), (ins imm0_255:$imm), NoItinerary,
+                   "subs", "\tpc, lr, $imm", []>, Requires<[IsThumb2]> {
+  let Inst{31-8} = 0b111100111101111010001111;
+
+  bits<8> imm;
+  let Inst{7-0} = imm;
+}
+
 //===----------------------------------------------------------------------===//
 // Non-Instruction Patterns
 //

llvm/lib/Target/ARM/AsmParser/ARMAsmParser.cpp

@@ -5138,6 +5138,26 @@ bool ARMAsmParser::ParseInstruction(ParseInstructionInfo &Info, StringRef Name,
     }
   }
 
+  // FIXME: As said above, this is all a pretty gross hack.  This instruction
+  // does not fit with other "subs" and tblgen.
+  // Adjust operands of B9.3.19 SUBS PC, LR, #imm (Thumb2) system instruction
+  // so the Mnemonic is the original name "subs" and delete the predicate
+  // operand so it will match the table entry.
+  if (isThumbTwo() && Mnemonic == "sub" && Operands.size() == 6 &&
+      static_cast<ARMOperand*>(Operands[3])->isReg() &&
+      static_cast<ARMOperand*>(Operands[3])->getReg() == ARM::PC &&
+      static_cast<ARMOperand*>(Operands[4])->isReg() &&
+      static_cast<ARMOperand*>(Operands[4])->getReg() == ARM::LR &&
+      static_cast<ARMOperand*>(Operands[5])->isImm()) {
+    ARMOperand *Op0 = static_cast<ARMOperand*>(Operands[0]);
+    Operands.erase(Operands.begin());
+    delete Op0;
+    Operands.insert(Operands.begin(), ARMOperand::CreateToken(Name, NameLoc));
+
+    ARMOperand *Op1 = static_cast<ARMOperand*>(Operands[1]);
+    Operands.erase(Operands.begin() + 1);
+    delete Op1;
+  }
   return false;
 }
 

llvm/test/MC/ARM/basic-thumb2-instructions.s

@@ -3588,3 +3588,7 @@ _func:
 @ rdar://12596361
          ldr r1, [pc, #12]
 @ CHECK: ldr r1, [pc, #12]              @ encoding: [0x03,0x49]
+
+@ rdar://14214063
+         subs pc, lr, #4
+@ CHECK: subs pc, lr, #4                @ encoding: [0xde,0xf3,0x04,0x8f]

llvm/test/MC/Disassembler/ARM/thumb2.txt

@@ -2051,6 +2051,7 @@
 # CHECK: sub.w r12, r6, #256
 # CHECK: subw r12, r6, #256
 # CHECK: subs.w r1, r2, #496
+# CHECK: subs pc, lr, #4
 
 0x0a 0xbf
 0x11 0x1f
@@ -2062,6 +2063,7 @@
 0xa6 0xf5 0x80 0x7c
 0xa6 0xf2 0x00 0x1c
 0xb2 0xf5 0xf8 0x71
+0xde 0xf3 0x04 0x8f
 
 
 #------------------------------------------------------------------------------