[llvm] [DAGCombiner] In mergeTruncStore, make sure we aren't storing shifted in bits. (PR #90939)

[Matt Arsenault via llvm-commits]

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@@ -35,7 +36,7 @@ enum RankFlags {
 // Get the rank for single-letter extension, lower value meaning higher
 // priority.
 static unsigned singleLetterExtensionRank(char Ext) {
-  assert(Ext >= 'a' && Ext <= 'z');
+  assert(isLower(Ext));
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arsenm wrote:

Unrelated change 

https://github.com/llvm/llvm-project/pull/90939