If a MachineBasicBlock has multiple ways of reaching another block,

allow it to have multiple CFG edges to that block. This is needed
to allow MachineBasicBlock::isOnlyReachableByFallthrough to work
correctly. This fixes PR4126.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@71018 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 28 insertions, 9 deletions

diff --git a/lib/CodeGen/IfConversion.cpp b/lib/CodeGen/IfConversion.cpp
index 8d212a6..b9ee23a 100644
--- a/lib/CodeGen/IfConversion.cpp
+++ b/lib/CodeGen/IfConversion.cpp
@@ -1174,8 +1174,7 @@ void IfConverter::CopyAndPredicateBlock(BBInfo &ToBBI, BBInfo &FromBBI,
     // Fallthrough edge can't be transferred.
     if (Succ == FallThrough)
       continue;
-    if (!ToBBI.BB->isSuccessor(Succ))
-      ToBBI.BB->addSuccessor(Succ);
+    ToBBI.BB->addSuccessor(Succ);
   }
 
   std::copy(FromBBI.Predicate.begin(), FromBBI.Predicate.end(),
@@ -1215,12 +1214,11 @@ void IfConverter::MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI) {
     if (Succ == FallThrough)
       continue;
     FromBBI.BB->removeSuccessor(Succ);
-    if (!ToBBI.BB->isSuccessor(Succ))
-      ToBBI.BB->addSuccessor(Succ);
+    ToBBI.BB->addSuccessor(Succ);
   }
 
   // Now FromBBI always fall through to the next block!
-  if (NBB && !FromBBI.BB->isSuccessor(NBB))
+  if (NBB)
     FromBBI.BB->addSuccessor(NBB);
 
   std::copy(FromBBI.Predicate.begin(), FromBBI.Predicate.end(),
diff --git a/lib/CodeGen/MachineBasicBlock.cpp b/lib/CodeGen/MachineBasicBlock.cpp
index 5ac54ea8..71e6b3e 100644
--- a/lib/CodeGen/MachineBasicBlock.cpp
+++ b/lib/CodeGen/MachineBasicBlock.cpp
@@ -305,11 +305,9 @@ void MachineBasicBlock::ReplaceUsesOfBlockWith(MachineBasicBlock *Old,
         I->getOperand(i).setMBB(New);
   }
 
-  // Update the successor information.  If New was already a successor, just
-  // remove the link to Old instead of creating another one.  PR 1444.
+  // Update the successor information.
   removeSuccessor(Old);
-  if (!isSuccessor(New))
-    addSuccessor(New);
+  addSuccessor(New);
 }
 
 /// CorrectExtraCFGEdges - Various pieces of code can cause excess edges in the
diff --git a/test/CodeGen/X86/omit-label.ll b/test/CodeGen/X86/omit-label.ll
new file mode 100644
index 0000000..457b66b
--- /dev/null
+++ b/test/CodeGen/X86/omit-label.ll
@@ -0,0 +1,23 @@
+; RUN: llvm-as < %s | llc -march=x86-64 | grep BB1_1:
+; PR4126
+
+; Don't omit this label's definition.
+
+define void @bux(i32 %p_53) nounwind optsize {
+entry:
+	%0 = icmp eq i32 %p_53, 0		; <i1> [#uses=1]
+	%1 = icmp sgt i32 %p_53, 0		; <i1> [#uses=1]
+	%or.cond = and i1 %0, %1		; <i1> [#uses=1]
+	br i1 %or.cond, label %bb.i, label %bb3
+
+bb.i:		; preds = %entry
+	%2 = add i32 %p_53, 1		; <i32> [#uses=1]
+	%3 = icmp slt i32 %2, 0		; <i1> [#uses=0]
+	br label %bb3
+
+bb3:		; preds = %bb.i, %entry
+	%4 = tail call i32 (...)* @baz(i32 0) nounwind		; <i32> [#uses=0]
+	ret void
+}
+
+declare i32 @baz(...)