svn commit: r258455 - head/contrib/llvm/lib/Target/X86

[Dimitry Andric]

Author: dim
Date: Thu Nov 21 23:09:07 2013
New Revision: 258455
URL: http://svnweb.freebsd.org/changeset/base/258455

Log:
  Pull in r195318 from upstream llvm trunk:
  
    The basic problem is that some mainstream programs cannot deal with the way
    clang optimizes tail calls, as in this example:
  
    int foo(void);
    int bar(void) {
    return foo();
    }
  
    where the call is transformed to:
  
     calll .L0$pb
    .L0$pb:
     popl  %eax
    .Ltmp0:
     addl  $_GLOBAL_OFFSET_TABLE_+(.Ltmp0-.L0$pb), %eax
     movl  foo at GOT(%eax), %eax
     popl  %ebp
     jmpl  *%eax                   # TAILCALL
  
    However, the GOT references must all be resolved at dlopen() time, and so this
    approach cannot be used with lazy dynamic linking (e.g. using RTLD_LAZY), which
    usually populates the PLT with stubs that perform the actual resolving.
  
    This patch changes X86TargetLowering::LowerCall() to skip tail call
    optimization, if the called function is a global or external symbol.
  
  This fixes problems with loading X.org driver modules, which could occur
  when X.org was compiled on i386 with tailcall optimization on, for which
  ports r312583 was committed as a workaround.  After this change, the
  workaround can be removed.
  
  MFC after:	3 days

Modified:
  head/contrib/llvm/lib/Target/X86/X86ISelLowering.cpp

Modified: head/contrib/llvm/lib/Target/X86/X86ISelLowering.cpp
==============================================================================
--- head/contrib/llvm/lib/Target/X86/X86ISelLowering.cpp	Thu Nov 21 23:00:09 2013	(r258454)
+++ head/contrib/llvm/lib/Target/X86/X86ISelLowering.cpp	Thu Nov 21 23:09:07 2013	(r258455)
@@ -2449,21 +2449,15 @@ X86TargetLowering::LowerCall(TargetLower
       RegsToPass.push_back(std::make_pair(unsigned(X86::EBX),
                DAG.getNode(X86ISD::GlobalBaseReg, DebugLoc(), getPointerTy())));
     } else {
-      // 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 at PLT. But for tail calls
-      // ebx would be restored (since ebx is callee saved) before jumping to the
-      // target at PLT.
-
-      // Note: The actual moving to ECX is done further down.
+      // 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.
       GlobalAddressSDNode *G = dyn_cast<GlobalAddressSDNode>(Callee);
-      if (G && !G->getGlobal()->hasHiddenVisibility() &&
-          !G->getGlobal()->hasProtectedVisibility())
-        Callee = LowerGlobalAddress(Callee, DAG);
-      else if (isa<ExternalSymbolSDNode>(Callee))
-        Callee = LowerExternalSymbol(Callee, DAG);
+      if ((G && !G->getGlobal()->hasHiddenVisibility() &&
+          !G->getGlobal()->hasProtectedVisibility()) ||
+          isa<ExternalSymbolSDNode>(Callee))
+        isTailCall = false;
     }
   }