[flang-commits] [flang] [flang] Use module file hashes for more checking and disambiguation (PR #80354)

[via flang-commits]

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@@ -1169,18 +1201,69 @@ static std::string CheckSum(const std::string_view &contents) {
   return result;
 }
 
-static bool VerifyHeader(llvm::ArrayRef<char> content) {
+std::optional<ModuleCheckSumType> ExtractCheckSum(const std::string_view &str) {
+  if (str.size() == ModHeader::sumLen) {
+    ModuleCheckSumType hash{0};
+    for (size_t j{0}; j < ModHeader::sumLen; ++j) {
+      hash <<= 4;
+      char ch{str.at(j)};
+      if (ch >= '0' && ch <= '9') {
+        hash += ch - '0';
+      } else if (ch >= 'a' && ch <= 'f') {
+        hash += ch - 'a' + 10;
+      } else {
+        return std::nullopt;
+      }
+    }
+    return hash;
+  }
+  return std::nullopt;
+}
+
+static std::optional<ModuleCheckSumType> VerifyHeader(
+    llvm::ArrayRef<char> content) {
   std::string_view sv{content.data(), content.size()};
   if (sv.substr(0, ModHeader::magicLen) != ModHeader::magic) {
-    return false;
+    return std::nullopt;
   }
+  ModuleCheckSumType checkSum{ComputeCheckSum(sv.substr(ModHeader::len))};
   std::string_view expectSum{sv.substr(ModHeader::magicLen, ModHeader::sumLen)};
-  std::string actualSum{CheckSum(sv.substr(ModHeader::len))};
-  return expectSum == actualSum;
+  if (auto extracted{ExtractCheckSum(expectSum)};
+      extracted && *extracted == checkSum) {
+    return checkSum;
+  } else {
+    return std::nullopt;
+  }
+}
+
+static void GetModuleDependences(
+    ModuleDependences &dependences, llvm::ArrayRef<char> content) {
+  std::size_t limit{content.size()};
+  std::string_view str{content.data(), limit};
+  for (std::size_t j{ModHeader::len}; str.substr(j, 7) == "!need$ ";) {
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jeanPerier wrote:

You could move the "!need$ " in a constexpr std::string_view to use the length instead of hard coding 7 here and below, and maybe use it in PutSymbols too when writing it.

https://github.com/llvm/llvm-project/pull/80354