Folding away unreachable case statement.

patch (slightly revised) by Aaron Ballman.

llvm-svn: 148359

1 files changed, 15 insertions, 7 deletions

diff --git a/clang/lib/CodeGen/CGStmt.cpp b/clang/lib/CodeGen/CGStmt.cpp
index ee4a272ea88..c7a8cf6a7d5 100644
--- a/clang/lib/CodeGen/CGStmt.cpp
+++ b/clang/lib/CodeGen/CGStmt.cpp
@@ -883,10 +883,8 @@ void CodeGenFunction::EmitCaseStmt(const CaseStmt &S) {
   // when we've constant-folded the switch, are emitting the constant case,
   // and part of the constant case includes another case statement.  For 
   // instance: switch (4) { case 4: do { case 5: } while (1); }
-  if (!SwitchInsn) {
-    EmitStmt(S.getSubStmt());
+  if (!SwitchInsn)
     return;
-  }
 
   // Handle case ranges.
   if (S.getRHS()) {
@@ -1162,6 +1160,10 @@ void CodeGenFunction::EmitSwitchStmt(const SwitchStmt &S) {
   if (S.getConditionVariable())
     EmitAutoVarDecl(*S.getConditionVariable());
 
+  // Handle nested switch statements.
+  llvm::SwitchInst *SavedSwitchInsn = SwitchInsn;
+  llvm::BasicBlock *SavedCRBlock = CaseRangeBlock;
+
   // See if we can constant fold the condition of the switch and therefore only
   // emit the live case statement (if any) of the switch.
   llvm::APInt ConstantCondValue;
@@ -1171,20 +1173,26 @@ void CodeGenFunction::EmitSwitchStmt(const SwitchStmt &S) {
                                    getContext())) {
       RunCleanupsScope ExecutedScope(*this);
 
+      // At this point, we are no longer "within" a switch instance, so
+      // we can temporarily enforce this to ensure that any embedded case
+      // statements are not emitted.
+      SwitchInsn = 0;
+
       // Okay, we can dead code eliminate everything except this case.  Emit the
       // specified series of statements and we're good.
       for (unsigned i = 0, e = CaseStmts.size(); i != e; ++i)
         EmitStmt(CaseStmts[i]);
+
+      // Now we want to restore the saved switch instance so that nested switches
+      // continue to function properly
+      SwitchInsn = SavedSwitchInsn;
+
       return;
     }
   }
     
   llvm::Value *CondV = EmitScalarExpr(S.getCond());
 
-  // Handle nested switch statements.
-  llvm::SwitchInst *SavedSwitchInsn = SwitchInsn;
-  llvm::BasicBlock *SavedCRBlock = CaseRangeBlock;
-
   // Create basic block to hold stuff that comes after switch
   // statement. We also need to create a default block now so that
   // explicit case ranges tests can have a place to jump to on