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


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187530 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 30 insertions, 0 deletions

diff --git a/lib/Target/ARM/ARMInstrThumb2.td b/lib/Target/ARM/ARMInstrThumb2.td
index 8e5e8c1735..842f3372d0 100644
--- a/lib/Target/ARM/ARMInstrThumb2.td
+++ b/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
 //
diff --git a/lib/Target/ARM/AsmParser/ARMAsmParser.cpp b/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
index 6d885a0d91..8e56a1ab94 100644
--- a/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
+++ b/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;
 }