ARM: provide diagnostics on more writeback LDM/STM instructions

The set of circumstances where the writeback register is allowed to be in the
list of registers is rather baroque, but I think this implements them all on
the assembly parsing side.

For disassembly, we still warn about an ARM-mode LDM even if the architecture
revision is < v7 (the required architecture information isn't available). It's
a silly instruction anyway, so hopefully no-one will mind.

rdar://problem/15223374

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@193185 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 41 insertions, 17 deletions

diff --git a/lib/Target/ARM/AsmParser/ARMAsmParser.cpp b/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
index 084ac9b0a1..7f2993d87f 100644
--- a/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
+++ b/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
@@ -5416,6 +5416,7 @@ validateInstruction(MCInst &Inst,
                    "bitfield width must be in range [1,32-lsb]");
     return false;
   }
+  // Notionally handles ARM::tLDMIA_UPD too.
   case ARM::tLDMIA: {
     // If we're parsing Thumb2, the .w variant is available and handles
     // most cases that are normally illegal for a Thumb1 LDM instruction.
@@ -5444,7 +5445,19 @@ validateInstruction(MCInst &Inst,
 
     break;
   }
-  case ARM::t2LDMIA_UPD: {
+  case ARM::LDMIA_UPD:
+  case ARM::LDMDB_UPD:
+  case ARM::LDMIB_UPD:
+  case ARM::LDMDA_UPD:
+    // ARM variants loading and updating the same register are only officially
+    // UNPREDICTABLE on v7 upwards. Goodness knows what they did before.
+    if (!hasV7Ops())
+      break;
+    // Fallthrough
+  case ARM::t2LDMIA_UPD:
+  case ARM::t2LDMDB_UPD:
+  case ARM::t2STMIA_UPD:
+  case ARM::t2STMDB_UPD: {
     if (listContainsReg(Inst, 3, Inst.getOperand(0).getReg()))
       return Error(Operands[4]->getStartLoc(),
                    "writeback operator '!' not allowed when base register "
@@ -5490,10 +5503,19 @@ validateInstruction(MCInst &Inst,
     break;
   }
   case ARM::tSTMIA_UPD: {
-    bool ListContainsBase;
-    if (checkLowRegisterList(Inst, 4, 0, 0, ListContainsBase) && !isThumbTwo())
+    bool ListContainsBase, InvalidLowList;
+    InvalidLowList = checkLowRegisterList(Inst, 4, Inst.getOperand(0).getReg(),
+                                          0, ListContainsBase);
+    if (InvalidLowList && !isThumbTwo())
       return Error(Operands[4]->getStartLoc(),
                    "registers must be in range r0-r7");
+
+    // This would be converted to a 32-bit stm, but that's not valid if the
+    // writeback register is in the list.
+    if (InvalidLowList && ListContainsBase)
+      return Error(Operands[4]->getStartLoc(),
+                   "writeback operator '!' not allowed when base register "
+                   "in register list");
     break;
   }
   case ARM::tADDrSP: {
diff --git a/lib/Target/ARM/Disassembler/ARMDisassembler.cpp b/lib/Target/ARM/Disassembler/ARMDisassembler.cpp
index 4872d73287..5be1b6957a 100644
--- a/lib/Target/ARM/Disassembler/ARMDisassembler.cpp
+++ b/lib/Target/ARM/Disassembler/ARMDisassembler.cpp
@@ -1203,20 +1203,22 @@ static DecodeStatus DecodeRegListOperand(MCInst &Inst, unsigned Val,
                                  uint64_t Address, const void *Decoder) {
   DecodeStatus S = MCDisassembler::Success;
 
-  bool writebackLoad = false;
-  unsigned writebackReg = 0;
+  bool NeedDisjointWriteback = false;
+  unsigned WritebackReg = 0;
   switch (Inst.getOpcode()) {
-    default:
-      break;
-    case ARM::LDMIA_UPD:
-    case ARM::LDMDB_UPD:
-    case ARM::LDMIB_UPD:
-    case ARM::LDMDA_UPD:
-    case ARM::t2LDMIA_UPD:
-    case ARM::t2LDMDB_UPD:
-      writebackLoad = true;
-      writebackReg = Inst.getOperand(0).getReg();
-      break;
+  default:
+    break;
+  case ARM::LDMIA_UPD:
+  case ARM::LDMDB_UPD:
+  case ARM::LDMIB_UPD:
+  case ARM::LDMDA_UPD:
+  case ARM::t2LDMIA_UPD:
+  case ARM::t2LDMDB_UPD:
+  case ARM::t2STMIA_UPD:
+  case ARM::t2STMDB_UPD:
+    NeedDisjointWriteback = true;
+    WritebackReg = Inst.getOperand(0).getReg();
+    break;
   }
 
   // Empty register lists are not allowed.
@@ -1226,7 +1228,7 @@ static DecodeStatus DecodeRegListOperand(MCInst &Inst, unsigned Val,
       if (!Check(S, DecodeGPRRegisterClass(Inst, i, Address, Decoder)))
         return MCDisassembler::Fail;
       // Writeback not allowed if Rn is in the target list.
-      if (writebackLoad && writebackReg == Inst.end()[-1].getReg())
+      if (NeedDisjointWriteback && WritebackReg == Inst.end()[-1].getReg())
         Check(S, MCDisassembler::SoftFail);
     }
   }