Merging r195439:

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r195439 | kcc | 2013-11-22 02:30:39 -0800 (Fri, 22 Nov 2013) | 3 lines

Revert r195318 as it causes miscompilation (PR18029)


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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_34@195478 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 14 insertions, 8 deletions

diff --git a/lib/Target/X86/X86ISelLowering.cpp b/lib/Target/X86/X86ISelLowering.cpp
index 0deb181..9df0232 100644
--- a/lib/Target/X86/X86ISelLowering.cpp
+++ b/lib/Target/X86/X86ISelLowering.cpp
@@ -2665,15 +2665,21 @@ X86TargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI,
       RegsToPass.push_back(std::make_pair(unsigned(X86::EBX),
                DAG.getNode(X86ISD::GlobalBaseReg, SDLoc(), getPointerTy())));
     } else {
-      // If we are tail calling a global or external symbol in GOT pic mode, we
-      // cannot use a direct jump, since that would make lazy dynamic linking
-      // impossible (see PR15086).  So pretend this is not a tail call, to
-      // prevent the optimization to a jump.
+      // If we are tail calling and generating PIC/GOT style code load the
+      // address of the callee into ECX. The value in ecx is used as target of
+      // the tail jump. This is done to circumvent the ebx/callee-saved problem
+      // for tail calls on PIC/GOT architectures. Normally we would just put the
+      // address of GOT into ebx and then call target@PLT. But for tail calls
+      // ebx would be restored (since ebx is callee saved) before jumping to the
+      // target@PLT.
+
+      // Note: The actual moving to ECX is done further down.
       GlobalAddressSDNode *G = dyn_cast<GlobalAddressSDNode>(Callee);
-      if ((G && !G->getGlobal()->hasHiddenVisibility() &&
-          !G->getGlobal()->hasProtectedVisibility()) ||
-          isa<ExternalSymbolSDNode>(Callee))
-        isTailCall = false;
+      if (G && !G->getGlobal()->hasHiddenVisibility() &&
+          !G->getGlobal()->hasProtectedVisibility())
+        Callee = LowerGlobalAddress(Callee, DAG);
+      else if (isa<ExternalSymbolSDNode>(Callee))
+        Callee = LowerExternalSymbol(Callee, DAG);
     }
   }