PPC QPX requires a 32-byte aligned stack

On systems which support the QPX vector instructions, the stack must be
32-byte aligned.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@173993 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/PowerPC/PPCSubtarget.cpp b/lib/Target/PowerPC/PPCSubtarget.cpp
index 91beeae..18e4c07 100644
--- a/lib/Target/PowerPC/PPCSubtarget.cpp
+++ b/lib/Target/PowerPC/PPCSubtarget.cpp
@@ -83,6 +83,12 @@
   // Set up darwin-specific properties.
   if (isDarwin())
     HasLazyResolverStubs = true;
+
+  // QPX requires a 32-byte aligned stack. Note that we need to do this if
+  // we're compiling for a BG/Q system regardless of whether or not QPX
+  // is enabled because external functions will assume this alignment.
+  if (hasQPX() || isBGQ())
+    StackAlignment = 32;
 }
 
 /// SetJITMode - This is called to inform the subtarget info that we are