[mips][mips16] Use isUnconditionalBranch() in AnalyzeBranch() and constant island pass.

[dsanders]

Summary

This stops it misidentifying unconditional branches as conditional branches
which fixes a -verify-machineinstrs error about exiting a function via fall through.

[sdardis]

LGTM.

lib/Target/Mips/MipsConstantIslandPass.cpp

static unsigned int branchTargetOperand(MachineInstr *MI) {
   case Mips::BeqzRxImmX16:
   case Mips::BnezRxImm16:
   case Mips::BnezRxImmX16:
     return 1;
   }
   llvm_unreachable("Unknown branch type");
 }
 
-static bool isUnconditionalBranch(unsigned int Opcode) {
-  switch (Opcode) {
-  default: return false;
-  case Mips::Bimm16:
-  case Mips::BimmX16:
-  case Mips::JalB16:
-    return true;
-  }
-}
-
 static unsigned int longformBranchOpcode(unsigned int Opcode) {
   switch (Opcode) {
   case Mips::Bimm16:
   case Mips::BimmX16:
     return Mips::BimmX16;
   case Mips::Bteqz16:
   case Mips::BteqzX16:
     return Mips::BteqzX16;
MipsConstantIslands::fixupConditionalBr(ImmBranch &Br) {
   MachineBasicBlock *MBB = MI->getParent();
   MachineInstr *BMI = &MBB->back();
   bool NeedSplit = (BMI != MI) || !BBHasFallthrough(MBB);
   unsigned OppositeBranchOpcode = TII->getOppositeBranchOpc(Opcode);
  
   ++NumCBrFixed;
   if (BMI != MI) {
     if (std::next(MachineBasicBlock::iterator(MI)) == std::prev(MBB->end()) &&
-        isUnconditionalBranch(BMI->getOpcode())) {
+        BMI->isUnconditionalBranch()) {
       // Last MI in the BB is an unconditional branch. Can we simply invert the
       // condition and swap destinations:
       // beqz L1
       // b   L2
       // =>
       // bnez L2
       // b   L1
       unsigned BMITargetOperand = branchTargetOperand(BMI);

lib/Target/Mips/MipsInstrInfo.cpp

if (++I != REnd) {
     // Not an analyzable branch (must be an indirect jump).
     if (isUnpredicatedTerminator(*SecondLastInst) && !SecondLastOpc)
       return BT_None;
   }
 
   // If there is only one terminator instruction, process it.
   if (!SecondLastOpc) {
     // Unconditional branch.
-    if (LastOpc == UncondBrOpc) {
+    if (LastInst->isUnconditionalBranch()) {
       TBB = LastInst->getOperand(0).getMBB();
       return BT_Uncond;
     }
 
     // Conditional branch
     AnalyzeCondBr(LastInst, LastOpc, TBB, Cond);
     return BT_Cond;
   }
 
   // If we reached here, there are two branches.
   // If there are three terminators, we don't know what sort of block this is.
   if (++I != REnd && isUnpredicatedTerminator(*I))
     return BT_None;
 
   BranchInstrs.insert(BranchInstrs.begin(), SecondLastInst);
 
   // If second to last instruction is an unconditional branch,
   // analyze it and remove the last instruction.
-  if (SecondLastOpc == UncondBrOpc) {
+  if (SecondLastInst->isUnconditionalBranch()) {
     // Return if the last instruction cannot be removed.
     if (!AllowModify)
       return BT_None;
 
     TBB = SecondLastInst->getOperand(0).getMBB();
     LastInst->eraseFromParent();
     BranchInstrs.pop_back();
     return BT_Uncond;
   }
 
   // Conditional branch followed by an unconditional branch.
   // The last one must be unconditional.
-  if (LastOpc != UncondBrOpc)
+  if (!LastInst->isUnconditionalBranch())
     return BT_None;
 
   AnalyzeCondBr(SecondLastInst, SecondLastOpc, TBB, Cond);
   FBB = LastInst->getOperand(0).getMBB();
 
   return BT_CondUncond;
 }
 

test/CodeGen/Mips/brsize3.ll

-; RUN: llc -mtriple=mipsel-linux-gnu -march=mipsel -mattr=mips16 -mattr=+soft-float -mips16-hard-float -relocation-model=pic -mips16-constant-islands   < %s | FileCheck %s -check-prefix=b-no-short
-
-; RUN: llc -mtriple=mipsel-linux-gnu -march=mipsel -mattr=mips16 -mattr=+soft-float -mips16-hard-float -relocation-model=pic -mips16-constant-islands   < %s | FileCheck %s -check-prefix=b-long
+; RUN: llc -mtriple=mipsel-linux-gnu -march=mipsel -mattr=mips16 \
+; RUN:     -mattr=+soft-float -mips16-hard-float -relocation-model=pic \
+; RUN:     -mips16-constant-islands -verify-machineinstrs  < %s | \
+; RUN:     FileCheck %s -check-prefix=b-no-short
+
+; RUN: llc -mtriple=mipsel-linux-gnu -march=mipsel -mattr=mips16 \
+; RUN:     -mattr=+soft-float -mips16-hard-float -relocation-model=pic \
+; RUN:     -mips16-constant-islands -verify-machineinstrs < %s | \
+; RUN:     FileCheck %s -check-prefix=b-long
 
 ; ModuleID = 'brsize3.c'
 target datalayout = "E-p:32:32:32-i1:8:8-i8:8:32-i16:16:32-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-n32-S64"
 target triple = "mips--linux-gnu"
 
 ; Function Attrs: noreturn nounwind optsize
 define void @foo() #0 {
 entry: