Add support for no-jump-tables

Add function soft attribute to the generation of Jump Tables in CodeGen
as initial step towards clang support of gcc's no-jump-table support

Reviewers: hans, echristo

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D18321

llvm-svn: 264756

1 files changed, 7 insertions, 2 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 0f610cee3b8..71c015df520 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -7961,7 +7961,12 @@ bool SelectionDAGBuilder::isDense(const CaseClusterVector &Clusters,
   return NumCases * 100 >= Range * Density;
 }
 
-static inline bool areJTsAllowed(const TargetLowering &TLI) {
+static inline bool areJTsAllowed(const TargetLowering &TLI,
+                                 const SwitchInst *SI) {
+  const Function *Fn = SI->getParent()->getParent();
+  if (Fn->getFnAttribute("no-jump-tables").getValueAsString() == "true")
+    return false;
+
   return TLI.isOperationLegalOrCustom(ISD::BR_JT, MVT::Other) ||
          TLI.isOperationLegalOrCustom(ISD::BRIND, MVT::Other);
 }
@@ -8055,7 +8060,7 @@ void SelectionDAGBuilder::findJumpTables(CaseClusterVector &Clusters,
 #endif
 
   const TargetLowering &TLI = DAG.getTargetLoweringInfo();
-  if (!areJTsAllowed(TLI))
+  if (!areJTsAllowed(TLI, SI))
     return;
 
   const int64_t N = Clusters.size();