Reapply 68073, with fixes. EH Landing-pad basic blocks are not

entered via fall-through. Don't miss fallthroughs from blocks
terminated by conditional branches. Also, move
isOnlyReachableByFallthrough out of line.

llvm-svn: 68129

3 files changed, 19 insertions, 1 deletions

diff --git a/llvm/include/llvm/CodeGen/MachineBasicBlock.h b/llvm/include/llvm/CodeGen/MachineBasicBlock.h
index 1ba7e798f83..134d22663b0 100644
--- a/llvm/include/llvm/CodeGen/MachineBasicBlock.h
+++ b/llvm/include/llvm/CodeGen/MachineBasicBlock.h
@@ -253,6 +253,11 @@ public:
   /// it returns end()
   iterator getFirstTerminator();
 
+  /// isOnlyReachableViaFallthough - Return true if this basic block has
+  /// exactly one predecessor and the control transfer mechanism between
+  /// the predecessor and this block is a fall-through.
+  bool isOnlyReachableByFallthrough() const;
+
   void pop_front() { Insts.pop_front(); }
   void pop_back() { Insts.pop_back(); }
   void push_back(MachineInstr *MI) { Insts.push_back(MI); }
diff --git a/llvm/lib/CodeGen/MachineBasicBlock.cpp b/llvm/lib/CodeGen/MachineBasicBlock.cpp
index 51f0f9d0001..5ac54ea8a44 100644
--- a/llvm/lib/CodeGen/MachineBasicBlock.cpp
+++ b/llvm/lib/CodeGen/MachineBasicBlock.cpp
@@ -123,6 +123,16 @@ MachineBasicBlock::iterator MachineBasicBlock::getFirstTerminator() {
   return I;
 }
 
+bool
+MachineBasicBlock::isOnlyReachableByFallthrough() const {
+  return !isLandingPad() &&
+         !pred_empty() &&
+         next(pred_begin()) == pred_end() &&
+         (*pred_begin())->isLayoutSuccessor(this) &&
+         ((*pred_begin())->empty() ||
+          !(*pred_begin())->back().getDesc().isBarrier());
+}
+
 void MachineBasicBlock::dump() const {
   print(*cerr.stream());
 }
diff --git a/llvm/lib/Target/X86/AsmPrinter/X86ATTAsmPrinter.cpp b/llvm/lib/Target/X86/AsmPrinter/X86ATTAsmPrinter.cpp
index 3bdcf88365f..3b6b0efec5a 100644
--- a/llvm/lib/Target/X86/AsmPrinter/X86ATTAsmPrinter.cpp
+++ b/llvm/lib/Target/X86/AsmPrinter/X86ATTAsmPrinter.cpp
@@ -238,7 +238,10 @@ bool X86ATTAsmPrinter::runOnMachineFunction(MachineFunction &MF) {
   for (MachineFunction::const_iterator I = MF.begin(), E = MF.end();
        I != E; ++I) {
     // Print a label for the basic block.
-    if (!I->pred_empty()) {
+    if (!VerboseAsm && (I->pred_empty() || I->isOnlyReachableByFallthrough())) {
+      // This is an entry block or a block that's only reachable via a
+      // fallthrough edge. In non-VerboseAsm mode, don't print the label.
+    } else {
       printBasicBlockLabel(I, true, true, VerboseAsm);
       O << '\n';
     }