[llvm] [memcpyopt] handle memcpy from memset in more cases (PR #140954)

[Nikita Popov via llvm-commits]

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@@ -1403,6 +1404,24 @@ static bool hasUndefContents(MemorySSA *MSSA, BatchAAResults &AA, Value *V,
   return false;
 }
 
+static bool coversInputFully(MemorySSA *MSSA, MemCpyInst *MemCpy,
+                             MemIntrinsic *MemSrc, BatchAAResults &BAA) {
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nikic wrote:

The name of this helper seems quite misleading. The corresponding boolean was previously called CanReduceSize, which is what this is actually checking (can we reduce CopySize to the size written by MemSrc).

https://github.com/llvm/llvm-project/pull/140954