Revert "Revert "Revert "[GlobalISel][IRTranslator] Emit trap intrinsi…

…c for "unreachable""""

This reverts commit c93bc50.

Seems to break a different thing now.

llvm/include/llvm/CodeGen/GlobalISel/IRTranslator.h

@@ -467,8 +467,9 @@ class IRTranslator : public MachineFunctionPass {
   bool translateSIToFP(const User &U, MachineIRBuilder &MIRBuilder) {
     return translateCast(TargetOpcode::G_SITOFP, U, MIRBuilder);
   }
-  bool translateUnreachable(const User &U, MachineIRBuilder &MIRBuilder);
-
+  bool translateUnreachable(const User &U, MachineIRBuilder &MIRBuilder) {
+    return true;
+  }
   bool translateSExt(const User &U, MachineIRBuilder &MIRBuilder) {
     return translateCast(TargetOpcode::G_SEXT, U, MIRBuilder);
   }

llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp

@@ -2701,28 +2701,6 @@ bool IRTranslator::translateVAArg(const User &U, MachineIRBuilder &MIRBuilder) {
   return true;
 }
 
-bool IRTranslator::translateUnreachable(const User &U, MachineIRBuilder &MIRBuilder) {
-    if (!MF->getTarget().Options.TrapUnreachable)
-    return true;
-
-  auto &UI = cast<UnreachableInst>(U);
-  // We may be able to ignore unreachable behind a noreturn call.
-  if (MF->getTarget().Options.NoTrapAfterNoreturn) {
-    const BasicBlock &BB = *UI.getParent();
-    if (&UI != &BB.front()) {
-      BasicBlock::const_iterator PredI =
-        std::prev(BasicBlock::const_iterator(UI));
-      if (const CallInst *Call = dyn_cast<CallInst>(&*PredI)) {
-        if (Call->doesNotReturn())
-          return true;
-      }
-    }
-  }
-
-  MIRBuilder.buildIntrinsic(Intrinsic::trap, ArrayRef<Register>(), true);
-  return true;
-}
-
 bool IRTranslator::translateInsertElement(const User &U,
                                           MachineIRBuilder &MIRBuilder) {
   // If it is a <1 x Ty> vector, use the scalar as it is

llvm/lib/CodeGen/GlobalISel/InstructionSelect.cpp

@@ -20,7 +20,6 @@
 #include "llvm/CodeGen/GlobalISel/InstructionSelector.h"
 #include "llvm/CodeGen/GlobalISel/LegalizerInfo.h"
 #include "llvm/CodeGen/GlobalISel/Utils.h"
-#include "llvm/CodeGen/MachineBasicBlock.h"
 #include "llvm/CodeGen/MachineOptimizationRemarkEmitter.h"
 #include "llvm/CodeGen/MachineFrameInfo.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
@@ -132,12 +131,8 @@ bool InstructionSelect::runOnMachineFunction(MachineFunction &MF) {
   const size_t NumBlocks = MF.size();
 #endif
 
-  // Keep track of selected blocks, so we can delete unreachable ones later.
-  DenseSet<MachineBasicBlock *> SelectedBlocks;
-
   for (MachineBasicBlock *MBB : post_order(&MF)) {
     ISel->CurMBB = MBB;
-    SelectedBlocks.insert(MBB);
     if (MBB->empty())
       continue;
 
@@ -206,20 +201,10 @@ bool InstructionSelect::runOnMachineFunction(MachineFunction &MF) {
     }
   }
 
-  SmallVector<MachineBasicBlock *> BlocksToDelete;
   for (MachineBasicBlock &MBB : MF) {
     if (MBB.empty())
       continue;
 
-    if (!SelectedBlocks.contains(&MBB)) {
-      // This is an unreachable block and therefore hasn't been selected, since
-      // the main selection loop above uses a postorder block traversal. Mark
-      // the block for deletion.
-      if (!MBB.hasAddressTaken())
-        BlocksToDelete.push_back(&MBB);
-      continue;
-    }
-
     // Try to find redundant copies b/w vregs of the same register class.
     bool ReachedBegin = false;
     for (auto MII = std::prev(MBB.end()), Begin = MBB.begin(); !ReachedBegin;) {
@@ -288,9 +273,6 @@ bool InstructionSelect::runOnMachineFunction(MachineFunction &MF) {
     return false;
   }
 #endif
-  for (auto *MBB : BlocksToDelete)
-    MBB->eraseFromParent();
-
   // Determine if there are any calls in this machine function. Ported from
   // SelectionDAG.
   MachineFrameInfo &MFI = MF.getFrameInfo();