[Local] Simplify the alignment limits in getOrEnforceKnownAlignment. …

…NFCI

We previously clamped the trailing zero count to 31 bits. And
then clamped the final alignment to MaximumAlignment which is
1 << 29.

This patch simplifies this to just clamp the trailing zero to
29 using MaxAlignmentExponent.

I was looking into changing this function to use Align/MaybeAlign
and noticed this.

Differential Revision: https://reviews.llvm.org/D78418

llvm/lib/Transforms/Utils/Local.cpp

@@ -1215,13 +1215,11 @@ unsigned llvm::getOrEnforceKnownAlignment(Value *V, unsigned PrefAlign,
 
   // Avoid trouble with ridiculously large TrailZ values, such as
   // those computed from a null pointer.
-  TrailZ = std::min(TrailZ, unsigned(sizeof(unsigned) * CHAR_BIT - 1));
+  // LLVM doesn't support alignments larger than (1 << MaxAlignmentExponent).
+  TrailZ = std::min(TrailZ, Value::MaxAlignmentExponent);
 
   unsigned Align = 1u << std::min(Known.getBitWidth() - 1, TrailZ);
 
-  // LLVM doesn't support alignments larger than this currently.
-  Align = std::min(Align, +Value::MaximumAlignment);
-
   if (PrefAlign > Align)
     Align = enforceKnownAlignment(V, Align, PrefAlign, DL);