ARM: Teach assembler to enforce constraints for ARM LDRD destination register operands.

As specified in A8.8.72/A8.8.73/A8.8.74 in the ARM ARM, all variants of the ARM LDRD instruction have the following two constraints:

LDRD<c> <Rt>, <Rt2>, ...

(a) Rt must be even-numbered and not r14
(b) Rt2 must be R(t+1)

If those two constraints are not met the result of executing the instruction will be unpredictable.

Constraint (b) was already enforced, this commit adds support for constraint (a).

Fixes rdar://14479793.

llvm-svn: 191520

1 files changed, 10 insertions, 1 deletions

diff --git a/llvm/lib/Target/ARM/AsmParser/ARMAsmParser.cpp b/llvm/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
index 14063eac1f5..6d6255f2cc2 100644
--- a/llvm/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
+++ b/llvm/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
@@ -5347,8 +5347,17 @@ validateInstruction(MCInst &Inst,
   case ARM::LDRD:
   case ARM::LDRD_PRE:
   case ARM::LDRD_POST: {
+    unsigned RtReg = Inst.getOperand(0).getReg();
+    // Rt can't be R14.
+    if (RtReg == ARM::LR)
+      return Error(Operands[3]->getStartLoc(),
+                   "Rt can't be R14");
+    unsigned Rt = MRI->getEncodingValue(RtReg);
+    // Rt must be even-numbered.
+    if ((Rt & 1) == 1)
+      return Error(Operands[3]->getStartLoc(),
+                   "Rt must be even-numbered");
     // Rt2 must be Rt + 1.
-    unsigned Rt = MRI->getEncodingValue(Inst.getOperand(0).getReg());
     unsigned Rt2 = MRI->getEncodingValue(Inst.getOperand(1).getReg());
     if (Rt2 != Rt + 1)
       return Error(Operands[3]->getStartLoc(),