[GlobalISel] Preserve IR block layout.

It makes the output function layout more predictable;  the layout has
an effect on performance, we don't want it to be at the mercy of the
translator's visitation order and such.
The predictable output is also easier to digest.

getOrCreateBB isn't appropriately named anymore, as it never needs to
create anything.  Rename it and extract the MBB creation logic out of it.

A couple tests were sensitive to the order. Update them.

llvm-svn: 297868

1 files changed, 26 insertions, 20 deletions

diff --git a/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp b/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp
index cf0c6600bec..2bcb5559101 100644
--- a/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp
@@ -140,15 +140,9 @@ unsigned IRTranslator::getMemOpAlignment(const Instruction &I) {
   return Alignment ? Alignment : DL->getABITypeAlignment(ValTy);
 }
 
-MachineBasicBlock &IRTranslator::getOrCreateBB(const BasicBlock &BB) {
+MachineBasicBlock &IRTranslator::getMBB(const BasicBlock &BB) {
   MachineBasicBlock *&MBB = BBToMBB[&BB];
-  if (!MBB) {
-    MBB = MF->CreateMachineBasicBlock(&BB);
-    MF->push_back(MBB);
-
-    if (BB.hasAddressTaken())
-      MBB->setHasAddressTaken();
-  }
+  assert(MBB && "BasicBlock was not encountered before");
   return *MBB;
 }
 
@@ -221,18 +215,18 @@ bool IRTranslator::translateBr(const User &U, MachineIRBuilder &MIRBuilder) {
     // We want a G_BRCOND to the true BB followed by an unconditional branch.
     unsigned Tst = getOrCreateVReg(*BrInst.getCondition());
     const BasicBlock &TrueTgt = *cast<BasicBlock>(BrInst.getSuccessor(Succ++));
-    MachineBasicBlock &TrueBB = getOrCreateBB(TrueTgt);
+    MachineBasicBlock &TrueBB = getMBB(TrueTgt);
     MIRBuilder.buildBrCond(Tst, TrueBB);
   }
 
   const BasicBlock &BrTgt = *cast<BasicBlock>(BrInst.getSuccessor(Succ));
-  MachineBasicBlock &TgtBB = getOrCreateBB(BrTgt);
+  MachineBasicBlock &TgtBB = getMBB(BrTgt);
   MIRBuilder.buildBr(TgtBB);
 
   // Link successors.
   MachineBasicBlock &CurBB = MIRBuilder.getMBB();
   for (const BasicBlock *Succ : BrInst.successors())
-    CurBB.addSuccessor(&getOrCreateBB(*Succ));
+    CurBB.addSuccessor(&getMBB(*Succ));
   return true;
 }
 
@@ -256,7 +250,7 @@ bool IRTranslator::translateSwitch(const User &U,
     MIRBuilder.buildICmp(CmpInst::ICMP_EQ, Tst, CaseValueReg, SwCondValue);
     MachineBasicBlock &CurMBB = MIRBuilder.getMBB();
     const BasicBlock *TrueBB = CaseIt.getCaseSuccessor();
-    MachineBasicBlock &TrueMBB = getOrCreateBB(*TrueBB);
+    MachineBasicBlock &TrueMBB = getMBB(*TrueBB);
 
     MIRBuilder.buildBrCond(Tst, TrueMBB);
     CurMBB.addSuccessor(&TrueMBB);
@@ -272,7 +266,7 @@ bool IRTranslator::translateSwitch(const User &U,
   }
   // handle default case
   const BasicBlock *DefaultBB = SwInst.getDefaultDest();
-  MachineBasicBlock &DefaultMBB = getOrCreateBB(*DefaultBB);
+  MachineBasicBlock &DefaultMBB = getMBB(*DefaultBB);
   MIRBuilder.buildBr(DefaultMBB);
   MachineBasicBlock &CurMBB = MIRBuilder.getMBB();
   CurMBB.addSuccessor(&DefaultMBB);
@@ -291,7 +285,7 @@ bool IRTranslator::translateIndirectBr(const User &U,
   // Link successors.
   MachineBasicBlock &CurBB = MIRBuilder.getMBB();
   for (const BasicBlock *Succ : BrInst.successors())
-    CurBB.addSuccessor(&getOrCreateBB(*Succ));
+    CurBB.addSuccessor(&getMBB(*Succ));
 
   return true;
 }
@@ -823,8 +817,8 @@ bool IRTranslator::translateInvoke(const User &U,
   MIRBuilder.buildInstr(TargetOpcode::EH_LABEL).addSym(EndSymbol);
 
   // FIXME: track probabilities.
-  MachineBasicBlock &EHPadMBB = getOrCreateBB(*EHPadBB),
-                    &ReturnMBB = getOrCreateBB(*ReturnBB);
+  MachineBasicBlock &EHPadMBB = getMBB(*EHPadBB),
+                    &ReturnMBB = getMBB(*ReturnBB);
   MF->addInvoke(&EHPadMBB, BeginSymbol, EndSymbol);
   MIRBuilder.getMBB().addSuccessor(&ReturnMBB);
   MIRBuilder.getMBB().addSuccessor(&EHPadMBB);
@@ -1128,13 +1122,25 @@ bool IRTranslator::runOnMachineFunction(MachineFunction &CurMF) {
   // Release the per-function state when we return, whether we succeeded or not.
   auto FinalizeOnReturn = make_scope_exit([this]() { finalizeFunction(); });
 
-  // Setup a separate basic-block for the arguments and constants, falling
-  // through to the IR-level Function's entry block.
+  // Setup a separate basic-block for the arguments and constants
   MachineBasicBlock *EntryBB = MF->CreateMachineBasicBlock();
   MF->push_back(EntryBB);
-  EntryBB->addSuccessor(&getOrCreateBB(F.front()));
   EntryBuilder.setMBB(*EntryBB);
 
+  // Create all blocks, in IR order, to preserve the layout.
+  for (const BasicBlock &BB: F) {
+    auto *&MBB = BBToMBB[&BB];
+
+    MBB = MF->CreateMachineBasicBlock(&BB);
+    MF->push_back(MBB);
+
+    if (BB.hasAddressTaken())
+      MBB->setHasAddressTaken();
+  }
+
+  // Make our arguments/constants entry block fallthrough to the IR entry block.
+  EntryBB->addSuccessor(&getMBB(F.front()));
+
   // Lower the actual args into this basic block.
   SmallVector<unsigned, 8> VRegArgs;
   for (const Argument &Arg: F.args())
@@ -1150,7 +1156,7 @@ bool IRTranslator::runOnMachineFunction(MachineFunction &CurMF) {
 
   // And translate the function!
   for (const BasicBlock &BB: F) {
-    MachineBasicBlock &MBB = getOrCreateBB(BB);
+    MachineBasicBlock &MBB = getMBB(BB);
     // Set the insertion point of all the following translations to
     // the end of this basic block.
     CurBuilder.setMBB(MBB);