[SDAGISel] Simplify some SDAGISel code, NFC

Hoist entry block code for arguments and swift error values out of the
basic block instruction selection loop. Lowering arguments once up front
seems much more readable than doing it conditionally inside the loop. It
also makes it clear that argument lowering can update StaticAllocaMap
because no instructions have been selected yet.

Also use range-based for loops where possible.

llvm-svn: 294329

1 files changed, 61 insertions, 58 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
index f3c916c6d9d..b45db5790ba 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
@@ -1287,7 +1287,6 @@ static void setupSwiftErrorVals(const Function &Fn, const TargetLowering *TLI,
 static void createSwiftErrorEntriesInEntryBlock(FunctionLoweringInfo *FuncInfo,
                                                 const TargetLowering *TLI,
                                                 const TargetInstrInfo *TII,
-                                                const BasicBlock *LLVMBB,
                                                 SelectionDAGBuilder *SDB) {
   if (!TLI->supportSwiftError())
     return;
@@ -1297,22 +1296,22 @@ static void createSwiftErrorEntriesInEntryBlock(FunctionLoweringInfo *FuncInfo,
   if (FuncInfo->SwiftErrorVals.empty())
     return;
 
-  if (pred_begin(LLVMBB) == pred_end(LLVMBB)) {
-    auto &DL = FuncInfo->MF->getDataLayout();
-    auto const *RC = TLI->getRegClassFor(TLI->getPointerTy(DL));
-    for (const auto *SwiftErrorVal : FuncInfo->SwiftErrorVals) {
-      // We will always generate a copy from the argument. It is always used at
-      // least by the 'return' of the swifterror.
-      if (FuncInfo->SwiftErrorArg && FuncInfo->SwiftErrorArg == SwiftErrorVal)
-        continue;
-      unsigned VReg = FuncInfo->MF->getRegInfo().createVirtualRegister(RC);
-      // Assign Undef to Vreg. We construct MI directly to make sure it works
-      // with FastISel.
-      BuildMI(*FuncInfo->MBB, FuncInfo->MBB->getFirstNonPHI(),
-              SDB->getCurDebugLoc(), TII->get(TargetOpcode::IMPLICIT_DEF),
-              VReg);
-      FuncInfo->setCurrentSwiftErrorVReg(FuncInfo->MBB, SwiftErrorVal, VReg);
-    }
+  assert(FuncInfo->MBB == &*FuncInfo->MF->begin() &&
+         "expected to insert into entry block");
+  auto &DL = FuncInfo->MF->getDataLayout();
+  auto const *RC = TLI->getRegClassFor(TLI->getPointerTy(DL));
+  for (const auto *SwiftErrorVal : FuncInfo->SwiftErrorVals) {
+    // We will always generate a copy from the argument. It is always used at
+    // least by the 'return' of the swifterror.
+    if (FuncInfo->SwiftErrorArg && FuncInfo->SwiftErrorArg == SwiftErrorVal)
+      continue;
+    unsigned VReg = FuncInfo->MF->getRegInfo().createVirtualRegister(RC);
+    // Assign Undef to Vreg. We construct MI directly to make sure it works
+    // with FastISel.
+    BuildMI(*FuncInfo->MBB, FuncInfo->MBB->getFirstNonPHI(),
+            SDB->getCurDebugLoc(), TII->get(TargetOpcode::IMPLICIT_DEF),
+            VReg);
+    FuncInfo->setCurrentSwiftErrorVReg(FuncInfo->MBB, SwiftErrorVal, VReg);
   }
 }
 
@@ -1442,12 +1441,47 @@ void SelectionDAGISel::SelectAllBasicBlocks(const Function &Fn) {
 
   setupSwiftErrorVals(Fn, TLI, FuncInfo);
 
-  // Iterate over all basic blocks in the function.
   ReversePostOrderTraversal<const Function*> RPOT(&Fn);
-  for (ReversePostOrderTraversal<const Function*>::rpo_iterator
-       I = RPOT.begin(), E = RPOT.end(); I != E; ++I) {
-    const BasicBlock *LLVMBB = *I;
 
+  // Lower arguments up front. An RPO iteration always visits the entry block
+  // first.
+  assert(*RPOT.begin() == &Fn.getEntryBlock());
+  ++NumEntryBlocks;
+
+  // Set up FuncInfo for ISel. Entry blocks never have PHIs.
+  FuncInfo->MBB = FuncInfo->MBBMap[&Fn.getEntryBlock()];
+  FuncInfo->InsertPt = FuncInfo->MBB->begin();
+
+  if (!FastIS) {
+    LowerArguments(Fn);
+  } else {
+    // See if fast isel can lower the arguments.
+    FastIS->startNewBlock();
+    if (!FastIS->lowerArguments()) {
+      // Fast isel failed to lower these arguments
+      ++NumFastIselFailLowerArguments;
+      if (EnableFastISelAbort > 1)
+        report_fatal_error("FastISel didn't lower all arguments");
+
+      // Use SelectionDAG argument lowering
+      LowerArguments(Fn);
+      CurDAG->setRoot(SDB->getControlRoot());
+      SDB->clear();
+      CodeGenAndEmitDAG();
+    }
+
+    // If we inserted any instructions at the beginning, make a note of
+    // where they are, so we can be sure to emit subsequent instructions
+    // after them.
+    if (FuncInfo->InsertPt != FuncInfo->MBB->begin())
+      FastIS->setLastLocalValue(&*std::prev(FuncInfo->InsertPt));
+    else
+      FastIS->setLastLocalValue(nullptr);
+  }
+  createSwiftErrorEntriesInEntryBlock(FuncInfo, TLI, TII, SDB);
+
+  // Iterate over all basic blocks in the function.
+  for (const BasicBlock *LLVMBB : RPOT) {
     if (OptLevel != CodeGenOpt::None) {
       bool AllPredsVisited = true;
       for (const_pred_iterator PI = pred_begin(LLVMBB), PE = pred_end(LLVMBB);
@@ -1479,8 +1513,9 @@ void SelectionDAGISel::SelectAllBasicBlocks(const Function &Fn) {
     FuncInfo->MBB = FuncInfo->MBBMap[LLVMBB];
     if (!FuncInfo->MBB)
       continue; // Some blocks like catchpads have no code or MBB.
-    FuncInfo->InsertPt = FuncInfo->MBB->getFirstNonPHI();
-    createSwiftErrorEntriesInEntryBlock(FuncInfo, TLI, TII, LLVMBB, SDB);
+
+    // Insert new instructions after any phi or argument setup code.
+    FuncInfo->InsertPt = FuncInfo->MBB->end();
 
     // Setup an EH landing-pad block.
     FuncInfo->ExceptionPointerVirtReg = 0;
@@ -1491,35 +1526,8 @@ void SelectionDAGISel::SelectAllBasicBlocks(const Function &Fn) {
 
     // Before doing SelectionDAG ISel, see if FastISel has been requested.
     if (FastIS) {
-      FastIS->startNewBlock();
-
-      // Emit code for any incoming arguments. This must happen before
-      // beginning FastISel on the entry block.
-      if (LLVMBB == &Fn.getEntryBlock()) {
-        ++NumEntryBlocks;
-
-        // Lower any arguments needed in this block if this is the entry block.
-        if (!FastIS->lowerArguments()) {
-          // Fast isel failed to lower these arguments
-          ++NumFastIselFailLowerArguments;
-          if (EnableFastISelAbort > 1)
-            report_fatal_error("FastISel didn't lower all arguments");
-
-          // Use SelectionDAG argument lowering
-          LowerArguments(Fn);
-          CurDAG->setRoot(SDB->getControlRoot());
-          SDB->clear();
-          CodeGenAndEmitDAG();
-        }
-
-        // If we inserted any instructions at the beginning, make a note of
-        // where they are, so we can be sure to emit subsequent instructions
-        // after them.
-        if (FuncInfo->InsertPt != FuncInfo->MBB->begin())
-          FastIS->setLastLocalValue(&*std::prev(FuncInfo->InsertPt));
-        else
-          FastIS->setLastLocalValue(nullptr);
-      }
+      if (LLVMBB != &Fn.getEntryBlock())
+        FastIS->startNewBlock();
 
       unsigned NumFastIselRemaining = std::distance(Begin, End);
       // Do FastISel on as many instructions as possible.
@@ -1626,13 +1634,8 @@ void SelectionDAGISel::SelectAllBasicBlocks(const Function &Fn) {
       }
 
       FastIS->recomputeInsertPt();
-    } else {
-      // Lower any arguments needed in this block if this is the entry block.
-      if (LLVMBB == &Fn.getEntryBlock()) {
-        ++NumEntryBlocks;
-        LowerArguments(Fn);
-      }
     }
+
     if (getAnalysis<StackProtector>().shouldEmitSDCheck(*LLVMBB)) {
       bool FunctionBasedInstrumentation =
           TLI->getSSPStackGuardCheck(*Fn.getParent());