reimplement codegen for indirect goto with the following advantages:

1. CGF now has fewer bytes of state (one pointer instead of a vector).
2. The generated code is determinstic, instead of getting labels in
   'map order' based on pointer addresses.
3. Clang now emits one 'indirect goto switch' for each function, instead
   of one for each indirect goto.  This fixes an M*N = N^2 IR size issue
   when there are lots of address-taken labels and lots of indirect gotos.
4. This also makes the default cause do something useful, reducing the
   size of the jump table needed (by one).

llvm-svn: 83952

1 files changed, 12 insertions, 5 deletions

diff --git a/clang/lib/CodeGen/CGStmt.cpp b/clang/lib/CodeGen/CGStmt.cpp
index 62e465d7028..f58b5792678 100644
--- a/clang/lib/CodeGen/CGStmt.cpp
+++ b/clang/lib/CodeGen/CGStmt.cpp
@@ -282,6 +282,7 @@ void CodeGenFunction::EmitGotoStmt(const GotoStmt &S) {
   EmitBranchThroughCleanup(getBasicBlockForLabel(S.getLabel()));
 }
 
+
 void CodeGenFunction::EmitIndirectGotoStmt(const IndirectGotoStmt &S) {
   // Emit initial switch which will be patched up later by
   // EmitIndirectSwitches(). We need a default dest, so we use the
@@ -289,11 +290,17 @@ void CodeGenFunction::EmitIndirectGotoStmt(const IndirectGotoStmt &S) {
   llvm::Value *V = Builder.CreatePtrToInt(EmitScalarExpr(S.getTarget()),
                                           llvm::Type::getInt32Ty(VMContext),
                                           "addr");
-  llvm::SwitchInst *I = Builder.CreateSwitch(V, Builder.GetInsertBlock());
-  IndirectSwitches.push_back(I);
-
-  // Clear the insertion point to indicate we are in unreachable code.
-  Builder.ClearInsertionPoint();
+  llvm::BasicBlock *CurBB = Builder.GetInsertBlock();
+  
+
+  // Get the basic block for the indirect goto.
+  llvm::BasicBlock *IndGotoBB = GetIndirectGotoBlock();
+  
+  // The first instruction in the block has to be the PHI for the switch dest,
+  // add an entry for this branch.
+  cast<llvm::PHINode>(IndGotoBB->begin())->addIncoming(V, CurBB);
+  
+  EmitBranch(IndGotoBB);
 }
 
 void CodeGenFunction::EmitIfStmt(const IfStmt &S) {