Handle BUNDLE instructions in MipsAsmPrinter

[arichardson]

Summary

In our CHERI fork we use BUNDLE instructions to ensure that a
three-instruction sequence to generate a program-counter-relative value is
emitted without reordering or insertions (since that would break the 32-bit
offset computation).

Currently MipsAsmPrinter asserts when it encounters a pseudo instruction.
To handle BUNDLE we can simply skip the instruction which will then make
EmitInstruction() process the contents of the bundle in order.

[merge_guards_bot]

Build result: pass - 60402 tests passed, 0 failed and 726 were skipped.

Log files: console-log.txt, CMakeCache.txt

[atanasyan]

LGTM

llvm/lib/Target/Mips/MipsAsmPrinter.cpp

void MipsAsmPrinter::EmitInstruction(const MachineInstr *MI) {
   MachineBasicBlock::const_instr_iterator I = MI->getIterator();
   MachineBasicBlock::const_instr_iterator E = MI->getParent()->instr_end();
 
   do {
     // Do any auto-generated pseudo lowerings.
     if (emitPseudoExpansionLowering(*OutStreamer, &*I))
       continue;
 
+    // Skip the BUNDLE pseudo instruction and lower the contents
+    if (I->isBundle())
+      continue;
+
     if (I->getOpcode() == Mips::PseudoReturn ||
         I->getOpcode() == Mips::PseudoReturn64 ||
         I->getOpcode() == Mips::PseudoIndirectBranch ||
         I->getOpcode() == Mips::PseudoIndirectBranch64 ||
         I->getOpcode() == Mips::TAILCALLREG ||
         I->getOpcode() == Mips::TAILCALLREG64) {
       emitPseudoIndirectBranch(*OutStreamer, &*I);
       continue;

llvm/test/CodeGen/Mips/delay-slot-filler-bundled-insts.mir

 # NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
 ## Check that the delay-slot filler does not attempt to split BUNDLE instructions
 # RUN: llc %s -start-before=mips-delay-slot-filler -stop-after=mips-delay-slot-filler \
 # RUN:   -verify-machineinstrs -o - | FileCheck %s
+## Check that we can emit assembly for input with BUNDLE instructions:
+# RUN: llc %s -start-before=mips-delay-slot-filler -verify-machineinstrs -o - | FileCheck %s -check-prefix ASM
+
+# ASM:  # %bb.0:
+# ASM-NEXT: daddiu  $sp, $sp, -16
+# ASM-NEXT: sd  $ra, 8($sp)
+## BUNDLE should be emitted in order:
+# ASM-NEXT: daddiu  $sp, $sp, -16
+# ASM-NEXT: daddiu  $sp, $sp, 16
+# ASM-NEXT: beqz  $4, .LBB0_2
+# ASM-NEXT: nop
 --- |
   target datalayout = "E-m:e-i8:8:32-i16:16:32-i64:64-n32:64-S128"
   target triple = "mips64-unknown-freebsd"
   declare i8* @func_a(i64 zeroext)
   declare i8* @func_b(i64 zeroext)
   ; Function Attrs: nounwind
   define i8* @test(i64 zeroext %nbytes) local_unnamed_addr #0 {
   entry: