GlobalISel: simplify MachineIRBuilder interface.

MachineIRBuilder had weird before/after and beginning/end flags for the insert
point. Unfortunately the non-default means that instructions will be inserted
in reverse order which is almost never what anyone wants.

Really, I think we just want (like IRBuilder has) the ability to insert at any
C++ iterator-style point (i.e. before any instruction or before MBB.end()). So
this fixes MIRBuilders to behave like IRBuilders in this respect.

llvm-svn: 288980

2 files changed, 21 insertions, 27 deletions

diff --git a/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp b/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp
index c986e65049f..726e89826c5 100644
--- a/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp
@@ -744,13 +744,18 @@ bool IRTranslator::runOnMachineFunction(MachineFunction &MF) {
 
   assert(PendingPHIs.empty() && "stale PHIs");
 
-  // Setup the arguments.
-  MachineBasicBlock &MBB = getOrCreateBB(F.front());
-  MIRBuilder.setMBB(MBB);
+  // Setup a separate basic-block for the arguments and constants, falling
+  // through to the IR-level Function's entry block.
+  MachineBasicBlock *EntryBB = MF.CreateMachineBasicBlock();
+  MF.push_back(EntryBB);
+  EntryBB->addSuccessor(&getOrCreateBB(F.front()));
+  EntryBuilder.setMBB(*EntryBB);
+
+  // Lower the actual args into this basic block.
   SmallVector<unsigned, 8> VRegArgs;
   for (const Argument &Arg: F.args())
     VRegArgs.push_back(getOrCreateVReg(Arg));
-  bool Succeeded = CLI->lowerFormalArguments(MIRBuilder, F, VRegArgs);
+  bool Succeeded = CLI->lowerFormalArguments(EntryBuilder, F, VRegArgs);
   if (!Succeeded) {
     if (!TPC->isGlobalISelAbortEnabled()) {
       MIRBuilder.getMF().getProperties().set(
@@ -761,13 +766,7 @@ bool IRTranslator::runOnMachineFunction(MachineFunction &MF) {
     report_fatal_error("Unable to lower arguments");
   }
 
-  // Now that we've got the ABI handling code, it's safe to set a location for
-  // any Constants we find in the IR.
-  if (MBB.empty())
-    EntryBuilder.setMBB(MBB, /* Beginning */ true);
-  else
-    EntryBuilder.setInstr(MBB.back(), /* Before */ false);
-
+  // And translate the function!
   for (const BasicBlock &BB: F) {
     MachineBasicBlock &MBB = getOrCreateBB(BB);
     // Set the insertion point of all the following translations to
diff --git a/llvm/lib/CodeGen/GlobalISel/MachineIRBuilder.cpp b/llvm/lib/CodeGen/GlobalISel/MachineIRBuilder.cpp
index d46dd9f6b8f..c04f6e4ae89 100644
--- a/llvm/lib/CodeGen/GlobalISel/MachineIRBuilder.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/MachineIRBuilder.cpp
@@ -27,34 +27,29 @@ void MachineIRBuilder::setMF(MachineFunction &MF) {
   this->MRI = &MF.getRegInfo();
   this->TII = MF.getSubtarget().getInstrInfo();
   this->DL = DebugLoc();
-  this->MI = nullptr;
+  this->II = MachineBasicBlock::iterator();
   this->InsertedInstr = nullptr;
 }
 
-void MachineIRBuilder::setMBB(MachineBasicBlock &MBB, bool Beginning) {
+void MachineIRBuilder::setMBB(MachineBasicBlock &MBB) {
   this->MBB = &MBB;
-  this->MI = nullptr;
-  Before = Beginning;
+  this->II = MBB.end();
   assert(&getMF() == MBB.getParent() &&
          "Basic block is in a different function");
 }
 
-void MachineIRBuilder::setInstr(MachineInstr &MI, bool Before) {
+void MachineIRBuilder::setInstr(MachineInstr &MI) {
   assert(MI.getParent() && "Instruction is not part of a basic block");
   setMBB(*MI.getParent());
-  this->MI = &MI;
-  this->Before = Before;
+  this->II = MI.getIterator();
 }
 
-MachineBasicBlock::iterator MachineIRBuilder::getInsertPt() {
-  if (MI) {
-    if (Before)
-      return MI;
-    if (!MI->getNextNode())
-      return getMBB().end();
-    return MI->getNextNode();
-  }
-  return Before ? getMBB().begin() : getMBB().end();
+void MachineIRBuilder::setInsertPt(MachineBasicBlock &MBB,
+                                   MachineBasicBlock::iterator II) {
+  assert(MBB.getParent() == &getMF() &&
+         "Basic block is in a different function");
+  this->MBB = &MBB;
+  this->II = II;
 }
 
 void MachineIRBuilder::recordInsertions(