Enable sibling call optimization of libcalls which are expanded during

legalization time. Since at legalization time there is no mapping from
SDNode back to the corresponding LLVM instruction and the return
SDNode is target specific, this requires a target hook to check for
eligibility. Only x86 and ARM support this form of sibcall optimization
right now.
rdar://8707777

llvm-svn: 120501

1 files changed, 18 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/Analysis.cpp b/llvm/lib/CodeGen/Analysis.cpp
index 2cf3c6666cd..36638c36de6 100644
--- a/llvm/lib/CodeGen/Analysis.cpp
+++ b/llvm/lib/CodeGen/Analysis.cpp
@@ -19,6 +19,7 @@
 #include "llvm/LLVMContext.h"
 #include "llvm/Module.h"
 #include "llvm/CodeGen/MachineFunction.h"
+#include "llvm/CodeGen/SelectionDAG.h"
 #include "llvm/Target/TargetData.h"
 #include "llvm/Target/TargetLowering.h"
 #include "llvm/Target/TargetOptions.h"
@@ -283,3 +284,20 @@ bool llvm::isInTailCallPosition(ImmutableCallSite CS, Attributes CalleeRetAttr,
   return true;
 }
 
+bool llvm::isInTailCallPosition(SelectionDAG &DAG, SDNode *Node,
+                                const TargetLowering &TLI) {
+  const Function *F = DAG.getMachineFunction().getFunction();
+
+  // Conservatively require the attributes of the call to match those of
+  // the return. Ignore noalias because it doesn't affect the call sequence.
+  unsigned CallerRetAttr = F->getAttributes().getRetAttributes();
+  if (CallerRetAttr & ~Attribute::NoAlias)
+    return false;
+
+  // It's not safe to eliminate the sign / zero extension of the return value.
+  if ((CallerRetAttr & Attribute::ZExt) || (CallerRetAttr & Attribute::SExt))
+    return false;
+
+  // Check if the only use is a function return node.
+  return TLI.isUsedByReturnOnly(Node);
+}