ARM: Teach assembler to enforce constraint for Thumb2 LDRD (literal/immediate) destination register operands.

LDRD<c> <Rt>, <Rt2>, <label>
LDRD<c> <Rt>, <Rt2>, [<Rn>{, #+/-<imm>}]
LDRD<c> <Rt>, <Rt2>, [<Rn>], #+/-<imm>
LDRD<c> <Rt>, <Rt2>, [<Rn>, #+/-<imm>]!

As specified in A8.8.72/A8.8.73 in the ARM ARM, the T1 encoding has a constraint which enforces that Rt != Rt2.

If this constraint is not met the result of executing the instruction will be unpredictable.

Fixes rdar://14479780.

llvm-svn: 191504

1 files changed, 11 insertions, 0 deletions

diff --git a/llvm/lib/Target/ARM/AsmParser/ARMAsmParser.cpp b/llvm/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
index edb7ccdc293..ce4933d8dfd 100644
--- a/llvm/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
+++ b/llvm/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
@@ -5355,6 +5355,17 @@ validateInstruction(MCInst &Inst,
                    "destination operands must be sequential");
     return false;
   }
+  case ARM::t2LDRDi8:
+  case ARM::t2LDRD_PRE:
+  case ARM::t2LDRD_POST: {
+    // Rt2 must different from Rt.
+    unsigned Rt = MRI->getEncodingValue(Inst.getOperand(0).getReg());
+    unsigned Rt2 = MRI->getEncodingValue(Inst.getOperand(1).getReg());
+    if (Rt2 == Rt)
+      return Error(Operands[3]->getStartLoc(),
+                   "destination operands can't be identical");
+    return false;
+  }
   case ARM::STRD: {
     // Rt2 must be Rt + 1.
     unsigned Rt = MRI->getEncodingValue(Inst.getOperand(0).getReg());