From: Dale Johannesen <dalej@apple.com>
Date: Wed, 23 Jun 2010 18:52:34 +0000 (+0000)
Subject: Do not do tail calls to external symbols.  If the
X-Git-Url: http://plrg.eecs.uci.edu/git/?a=commitdiff_plain;h=e39fdbe1187b74f8c415adb9f807fa56f1e055aa;p=oota-llvm.git

Do not do tail calls to external symbols.  If the
branch turns out to be ARM-to-Thumb or vice versa
the linker cannot resolve this.  8120438.

If this optimization is going to be useful we probably
need a compiler flag "assume callees are same architecture"
or something like that.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@106662 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Target/ARM/ARMISelLowering.cpp b/lib/Target/ARM/ARMISelLowering.cpp
index 97a5f9da120..ceb6806f6d5 100644
--- a/lib/Target/ARM/ARMISelLowering.cpp
+++ b/lib/Target/ARM/ARMISelLowering.cpp
@@ -1408,29 +1408,26 @@ ARMTargetLowering::IsEligibleForTailCallOptimization(SDValue Callee,
   if (isCalleeStructRet || isCallerStructRet)
     return false;
 
-  // FIXME: Completely disable sibcal for Thumb1 since Thumb1RegisterInfo::
+  // FIXME: Completely disable sibcall for Thumb1 since Thumb1RegisterInfo::
   // emitEpilogue is not ready for them.
   if (Subtarget->isThumb1Only())
     return false;
 
+  // For the moment, we can only do this to functions defined in this
+  // compilation, or to indirect calls.  A Thumb B to an ARM function,
+  // or vice versa, is not easily fixed up in the linker unlike BL.
+  // (We could do this by loading the address of the callee into a register;
+  // that is an extra instruction over the direct call and burns a register
+  // as well, so is not likely to be a win.)
   if (isa<ExternalSymbolSDNode>(Callee))
       return false;
 
   if (GlobalAddressSDNode *G = dyn_cast<GlobalAddressSDNode>(Callee)) {
-    if (Subtarget->isThumb1Only())
+    const GlobalValue *GV = G->getGlobal();
+    if (GV->isDeclaration() || GV->isWeakForLinker())
       return false;
-
-    // On Thumb, for the moment, we can only do this to functions defined in this
-    // compilation, or to indirect calls.  A Thumb B to an ARM function is not
-    // easily fixed up in the linker, unlike BL.
-    if (Subtarget->isThumb()) {
-      const GlobalValue *GV = G->getGlobal();
-      if (GV->isDeclaration() || GV->isWeakForLinker())
-        return false;
-    }
   }
 
-
   // If the calling conventions do not match, then we'd better make sure the
   // results are returned in the same way as what the caller expects.
   if (!CCMatch) {