Fix a miscompilation I introduced in r129652, thanks for Eli for tracking

it down.  we effectively were compile the testcase into:

void test14(int x) {
  switch (x) {
    case 11: break;
    case 42: test14(97);  // fallthrough
    default: test14(42); break;

which is not the same thing at all.  This fixes a miscompilation of 
MallocBench/gs seen on the clang-x86_64-linux-fnt buildbot.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@129679 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 25 insertions, 1 deletions

diff --git a/lib/CodeGen/CGStmt.cpp b/lib/CodeGen/CGStmt.cpp
index b8b2cd9f3e..8bb45343db 100644
--- a/lib/CodeGen/CGStmt.cpp
+++ b/lib/CodeGen/CGStmt.cpp
@@ -873,7 +873,8 @@ void CodeGenFunction::EmitCaseStmt(const CaseStmt &S) {
     return;
   }
 
-  // If the body of the case is just a 'break', try to not emit an empty block.
+  // If the body of the case is just a 'break', and if there was no fallthrough,
+  // try to not emit an empty block.
   if (isa<BreakStmt>(S.getSubStmt())) {
     JumpDest Block = BreakContinueStack.back().BreakBlock;
     
@@ -882,6 +883,13 @@ void CodeGenFunction::EmitCaseStmt(const CaseStmt &S) {
       llvm::APSInt CaseVal = S.getLHS()->EvaluateAsInt(getContext());
       SwitchInsn->addCase(llvm::ConstantInt::get(getLLVMContext(), CaseVal),
                           Block.getBlock());
+
+      // If there was a fallthrough into this case, make sure to redirect it to
+      // the end of the switch as well.
+      if (Builder.GetInsertBlock()) {
+        Builder.CreateBr(Block.getBlock());
+        Builder.ClearInsertionPoint();
+      }
       return;
     }
   }
diff --git a/test/CodeGen/switch-dce.c b/test/CodeGen/switch-dce.c
index 4013809cbf..bbb5f7e5aa 100644
--- a/test/CodeGen/switch-dce.c
+++ b/test/CodeGen/switch-dce.c
@@ -229,3 +229,19 @@ void test13(int x) {
   default: test13(42); break;
   }
 }
+
+
+// Verify that case 42 only calls test14 once.
+// CHECK: @test14
+// CHECK: call void @test14(i32 97)
+// CHECK-NEXT: br label [[EPILOG2:%[0-9.a-z]+]]
+// CHECK: call void @test14(i32 42)
+// CHECK-NEXT: br label [[EPILOG2]]
+void test14(int x) {
+  switch (x) {
+    case 42: test14(97);  // fallthrough
+    case 11: break;
+    default: test14(42); break;
+  }
+}
+