diff -r 000000000000 -r 6474c204b198 build/autoconf/gcc-pr49911.m4
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/build/autoconf/gcc-pr49911.m4	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,71 @@
+dnl This Source Code Form is subject to the terms of the Mozilla Public
+dnl License, v. 2.0. If a copy of the MPL was not distributed with this
+dnl file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+dnl Check if the compiler is gcc and has PR49911. If so
+dnl disable vrp.
+
+AC_DEFUN([MOZ_GCC_PR49911],
+[
+if test "$GNU_CC"; then
+
+AC_MSG_CHECKING(for gcc PR49911)
+ac_have_gcc_pr49911="no"
+AC_LANG_SAVE
+AC_LANG_CPLUSPLUS
+
+_SAVE_CXXFLAGS=$CXXFLAGS
+CXXFLAGS="-O2"
+AC_TRY_RUN([
+extern "C" void abort(void);
+typedef enum {
+eax,         ecx,         edx,         ebx,         esp,         ebp,
+esi,         edi     }
+RegisterID;
+union StateRemat {
+  RegisterID reg_;
+  int offset_;
+};
+static StateRemat FromRegister(RegisterID reg) {
+  StateRemat sr;
+  sr.reg_ = reg;
+  return sr;
+}
+static StateRemat FromAddress3(int address) {
+  StateRemat sr;
+  sr.offset_ = address;
+  if (address < 46 &&    address >= 0) {
+    abort();
+  }
+  return sr;
+}
+struct FrameState {
+  StateRemat dataRematInfo2(bool y, int z) {
+    if (y)         return FromRegister(RegisterID(1));
+    return FromAddress3(z);
+  }
+};
+FrameState frame;
+StateRemat x;
+__attribute__((noinline)) void jsop_setelem(bool y, int z) {
+  x = frame.dataRematInfo2(y, z);
+}
+int main(void) {
+  jsop_setelem(0, 47);
+}
+], true,
+   ac_have_gcc_pr49911="yes",
+   true)
+CXXFLAGS="$_SAVE_CXXFLAGS"
+
+AC_LANG_RESTORE
+
+if test "$ac_have_gcc_pr49911" = "yes"; then
+   AC_MSG_RESULT(yes)
+   CFLAGS="$CFLAGS -fno-tree-vrp"
+   CXXFLAGS="$CXXFLAGS -fno-tree-vrp"
+else
+   AC_MSG_RESULT(no)
+fi
+fi
+])