Use the asmprinter to find out what the preferred alignment of a global is.

This patch speeds up 172.mgrid from 31.81s to 11.39s on darwin/ppc.
Many many thanks to Nate for tracking down the root cause of the issue.

llvm-svn: 25979

llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp

@@ -527,7 +527,7 @@ bool DarwinAsmPrinter::doFinalization(Module &M) {
     std::string name = Mang->getValueName(I);
     Constant *C = I->getInitializer();
     unsigned Size = TD.getTypeSize(C->getType());
-    unsigned Align = TD.getTypeAlignmentShift(C->getType());
+    unsigned Align = getPreferredAlignmentLog(I);
 
     if (C->isNullValue() && /* FIXME: Verify correct */
         (I->hasInternalLinkage() || I->hasWeakLinkage() ||