[lld] [lld][ELF] Add `--why-extract` for bitcode libcalls (PR #78781)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-lld-elf

@llvm/pr-subscribers-lld-wasm

Author: Sam Clegg (sbc100)

<details>
<summary>Changes</summary>

The Wasm linker already records these and its seems useful to do so.

Also mirror the simplications of this function from # in the Wasm linker #<!-- -->78659.

---
Full diff: https://github.com/llvm/llvm-project/pull/78781.diff


2 Files Affected:

- (modified) lld/ELF/Driver.cpp (+4-1) 
- (modified) lld/wasm/Driver.cpp (+4-10) 


``````````diff
diff --git a/lld/ELF/Driver.cpp b/lld/ELF/Driver.cpp
index 07f4263c90e62b3..6e9b6ba6a2476b1 100644
--- a/lld/ELF/Driver.cpp
+++ b/lld/ELF/Driver.cpp
@@ -2081,8 +2081,11 @@ static void handleUndefinedGlob(StringRef arg) {
 
 static void handleLibcall(StringRef name) {
   Symbol *sym = symtab.find(name);
-  if (sym && sym->isLazy() && isa<BitcodeFile>(sym->file))
+  if (sym && sym->isLazy() && isa<BitcodeFile>(sym->file)) {
+    if (!config->whyExtract.empty())
+      ctx.whyExtractRecords.emplace_back("<libcall>", sym->file, *sym);
     sym->extract();
+  }
 }
 
 static void writeArchiveStats() {
diff --git a/lld/wasm/Driver.cpp b/lld/wasm/Driver.cpp
index 4a4f9a96227946d..862d095dc105184 100644
--- a/lld/wasm/Driver.cpp
+++ b/lld/wasm/Driver.cpp
@@ -716,16 +716,10 @@ static Symbol *handleUndefined(StringRef name, const char *option) {
 
 static void handleLibcall(StringRef name) {
   Symbol *sym = symtab->find(name);
-  if (!sym)
-    return;
-
-  if (auto *lazySym = dyn_cast<LazySymbol>(sym)) {
-    MemoryBufferRef mb = lazySym->getMemberBuffer();
-    if (isBitcode(mb)) {
-      if (!config->whyExtract.empty())
-        ctx.whyExtractRecords.emplace_back("<libcall>", sym->getFile(), *sym);
-      lazySym->extract();
-    }
+  if (sym && sym->isLazy() && isa<BitcodeFile>(sym->file)) {
+    if (!config->whyExtract.empty())
+      ctx.whyExtractRecords.emplace_back("<libcall>", sym->getFile(), *sym);
+    lazySym->extract();
   }
 }
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/78781