Cherry-pick LLVM 187787 to prevent tail calls on x86-32 when not appropriate.

See:
http://llvm.org/viewvc/llvm-project?view=revision&revision=187787

The newer version of newlib tickles this x86-32 bug
when building the exception handling tests, which don't
strip the "tail" attribute.

BUG=https://code.google.com/p/nativeclient/issues/detail?id=3702

Waiting on trybots, but it seems to have fixed the minimal
reproducer I have:
http://chromegw.corp.google.com/i/tryserver.nacl/builders/nacl-toolchain-linux-pnacl-x86_64/builds/922
http://chromegw.corp.google.com/i/tryserver.nacl/builders/nacl-toolchain-linux-pnacl-x86_32/builds/870
http://chromegw.corp.google.com/i/tryserver.nacl/builders/nacl-toolchain-mac-pnacl-x86_32/builds/875

R=jfb@chromium.org

Review URL: https://codereview.chromium.org/26538008

1 files changed, 9 insertions, 0 deletions

diff --git a/include/llvm/Target/TargetLowering.h b/include/llvm/Target/TargetLowering.h
index 091368382e..b49eeb2eea 100644
--- a/include/llvm/Target/TargetLowering.h
+++ b/include/llvm/Target/TargetLowering.h
@@ -1176,6 +1176,15 @@ public:
     return false;
   }
 
+  /// Return true if a truncation from Ty1 to Ty2 is permitted when deciding
+  /// whether a call is in tail position. Typically this means that both results
+  /// would be assigned to the same register or stack slot, but it could mean
+  /// the target performs adequate checks of its own before proceeding with the
+  /// tail call.
+  virtual bool allowTruncateForTailCall(Type * /*Ty1*/, Type * /*Ty2*/) const {
+    return false;
+  }
+
   virtual bool isTruncateFree(EVT /*VT1*/, EVT /*VT2*/) const {
     return false;
   }