[llvm] [ThinLTO] Don't mark calloc function dead (PR #72673)

[Fangrui Song via llvm-commits]

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@@ -54,6 +54,10 @@ static const char *PreservedSymbols[] = {
     // TODO: Are there similar such variables?
     "__ssp_canary_word",
     "__stack_chk_guard",
+    // The dead store elimination pass can fold malloc + memset calls into
+    // a single call to calloc. Prevent thin LTO from marking calloc a dead
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MaskRay wrote:

// Prevent thin LTO from marking calloc a dead function ...

I think this sentence can be removed, as it describes the problem that applies too all preserved symbols, which can use a comment applying to the whole variable.

This change affects regular LTO, so "thin LTO" is not accurate. This list also prevents internalization.

https://github.com/llvm/llvm-project/pull/72673