Disable x86 tail call optimizations that jump through GOT

For x86 targets, do not do sibling call optimization when materializing
the callee's address would require a GOT relocation. We can still do
tail calls to internal functions, hidden functions, and protected
functions, because they do not require this kind of relocation. It is
still possible to get GOT relocations when the user explicitly asks for
it with musttail or -tailcallopt, both of which are supposed to
guarantee TCO.

Based on a patch by Chih-hung Hsieh.

Reviewers: srhines, timmurray, danalbert, enh, void, nadav, rnk

Subscribers: joerg, davidxl, llvm-commits

Differential Revision: http://reviews.llvm.org/D9799

llvm-svn: 238487

1 files changed, 20 insertions, 2 deletions

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index fb600e0b577..75e03a50f39 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -2780,6 +2780,24 @@ X86TargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI,
   if (MF.getTarget().Options.DisableTailCalls)
     isTailCall = false;
 
+  if (Subtarget->isPICStyleGOT() &&
+      !MF.getTarget().Options.GuaranteedTailCallOpt) {
+    // If we are using a GOT, disable tail calls to external symbols with
+    // default visibility. Tail calling such a symbol requires using a GOT
+    // relocation, which forces early binding of the symbol. This breaks code
+    // that require lazy function symbol resolution. Using musttail or
+    // GuaranteedTailCallOpt will override this.
+    GlobalAddressSDNode *G = dyn_cast<GlobalAddressSDNode>(Callee);
+    if (!G || (!G->getGlobal()->hasLocalLinkage() &&
+               G->getGlobal()->hasDefaultVisibility())) {
+      isTailCall = false;
+      if (G) {
+        llvm::errs() << "disabling tail call for default visibility symbol\n";
+        G->getGlobal()->dump();
+      }
+    }
+  }
+
   bool IsMustTail = CLI.CS && CLI.CS->isMustTailCall();
   if (IsMustTail) {
     // Force this to be a tail call.  The verifier rules are enough to ensure
@@ -2964,8 +2982,8 @@ X86TargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI,
 
       // Note: The actual moving to ECX is done further down.
       GlobalAddressSDNode *G = dyn_cast<GlobalAddressSDNode>(Callee);
-      if (G && !G->getGlobal()->hasHiddenVisibility() &&
-          !G->getGlobal()->hasProtectedVisibility())
+      if (G && !G->getGlobal()->hasLocalLinkage() &&
+          G->getGlobal()->hasDefaultVisibility())
         Callee = LowerGlobalAddress(Callee, DAG);
       else if (isa<ExternalSymbolSDNode>(Callee))
         Callee = LowerExternalSymbol(Callee, DAG);