[Stack Alignment] emit warning instead of a hard error

Per discussion in rdar://13127907, we should emit a hard error only if
people write code where the requested alignment is larger than achievable
and assumes the low bits are zeros. A warning should be good enough when
we are not sure if the source code assumes the low bits are zeros.

rdar://13127907


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@174336 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/MachineFunction.cpp b/lib/CodeGen/MachineFunction.cpp
index 3d7d20d..4a9a62a 100644
--- a/lib/CodeGen/MachineFunction.cpp
+++ b/lib/CodeGen/MachineFunction.cpp
@@ -479,11 +479,11 @@
   if (!ShouldClamp || PrefAlign <= StackAlign)
     return PrefAlign;
   if (Alloca && MinAlign > StackAlign)
-    Alloca->getParent()->getContext().emitError(Alloca,
-        "Requested Minimal Alignment exceeds the Stack Alignment!");
+    Alloca->getParent()->getContext().emitWarning(Alloca,
+        "Requested alignment exceeds the stack alignment!");
   else
     assert(MinAlign <= StackAlign &&
-           "Requested Minimal Alignment exceeds the Stack Alignment!");
+           "Requested alignment exceeds the stack alignment!");
   return StackAlign;
 }