[mips][ias] Prevent double-filling of delay slots by generating '.set noreorder' regions.

[dsanders]

Summary

When clang is given -save-temps or -via-file-asm, any inline assembly in
the source is parsed twice. Once by the compiler, and again by the
assembler. We must take care to ensure that this doesn't lead to
double-filling delay slots.

Depends on D19164

[vkalintiris]

LGTM.

lib/Target/Mips/AsmParser/MipsAsmParser.cpp

switch (Inst.getOpcode()) {
           return Error(IDLoc, "expected immediate operand kind");
         int Imm = Opnd.getImm();
         if ((Imm % 4 != 0) || !isInt<25>(Imm))
           return Error(IDLoc, "immediate operand value out of range");
         break;
     }
   }
 
+  bool FillDelaySlot =
+      MCID.hasDelaySlot() && AssemblerOptions.back()->isReorder();
+  if (FillDelaySlot)
+    getTargetStreamer().emitDirectiveSetNoReorder();
+
   MacroExpanderResultTy ExpandResult =
       tryExpandInstruction(Inst, IDLoc, Out, STI);
   switch (ExpandResult) {
   case MER_NotAMacro:
     Out.EmitInstruction(Inst, *STI);
     break;
   case MER_Success:
     break;
   case MER_Fail:
     return true;
   }
 
   // If this instruction has a delay slot and .set reorder is active,
   // emit a NOP after it.
-  if (MCID.hasDelaySlot() && AssemblerOptions.back()->isReorder())
+  if (FillDelaySlot) {
     createNop(hasShortDelaySlot(Inst.getOpcode()), IDLoc, Out, STI);
+    getTargetStreamer().emitDirectiveSetReorder();
+  }
 
   if ((Inst.getOpcode() == Mips::JalOneReg ||
        Inst.getOpcode() == Mips::JalTwoReg || ExpandedJalSym) &&
       isPicAndNotNxxAbi()) {
     if (IsCpRestoreSet) {
       // We need a NOP between the JALR and the LW:
       // If .set reorder has been used, we've already emitted a NOP.
       // If .set noreorder has been used, we need to emit a NOP at this point.

test/MC/Mips/double-expand.s

+# RUN: llvm-mc -triple=mipsel-unknown-linux < %s | FileCheck %s
+# RUN: llvm-mc -triple=mipsel-unknown-linux < %s | \
+# RUN:     llvm-mc -triple=mipsel-unknown-linux | FileCheck %s
+
+# CHECK: bnez $2, foo
+# CHECK: nop
+# CHECK-NOT: nop
+
+        .text
+  bnez $2, foo