[llvm-readobj] Use heterogenous lookups with std::map (NFC)

[kazutakahirata]

Heterogenous lookups allow us to call find with StringRef, avoiding a
temporary heap allocation of std::string.

[llvmbot]

@llvm/pr-subscribers-llvm-binary-utilities

Author: Kazu Hirata (kazutakahirata)

Changes

---

Full diff: https://github.com/llvm/llvm-project/pull/114929.diff

1 Files Affected:

• (modified) llvm/tools/llvm-readobj/ObjDumper.cpp (+2-2)

diff --git a/llvm/tools/llvm-readobj/ObjDumper.cpp b/llvm/tools/llvm-readobj/ObjDumper.cpp
index d02d1e543d31dc..d3c613ee823bae 100644
--- a/llvm/tools/llvm-readobj/ObjDumper.cpp
+++ b/llvm/tools/llvm-readobj/ObjDumper.cpp
@@ -106,7 +106,7 @@ static std::vector<object::SectionRef>
 getSectionRefsByNameOrIndex(const object::ObjectFile &Obj,
                             ArrayRef<std::string> Sections) {
   std::vector<object::SectionRef> Ret;
-  std::map<std::string, bool> SecNames;
+  std::map<std::string, bool, std::less<>> SecNames;
   std::map<unsigned, bool> SecIndices;
   unsigned SecIndex;
   for (StringRef Section : Sections) {
@@ -119,7 +119,7 @@ getSectionRefsByNameOrIndex(const object::ObjectFile &Obj,
   SecIndex = Obj.isELF() ? 0 : 1;
   for (object::SectionRef SecRef : Obj.sections()) {
     StringRef SecName = unwrapOrError(Obj.getFileName(), SecRef.getName());
-    auto NameIt = SecNames.find(std::string(SecName));
+    auto NameIt = SecNames.find(SecName);
     if (NameIt != SecNames.end())
       NameIt->second = true;
     auto IndexIt = SecIndices.find(SecIndex);

[jh7370]

Functionally LGTM, but the commit title is unhelpful, in my opinion. I'd suggest adding a description of "Support lookups in a section name std::map with both std::string and StringRef" or something to that effect (I'd suggest this be the title, but it's too long probably, so the description will have to do).

[kazutakahirata]

Functionally LGTM, but the commit title is unhelpful, in my opinion. I'd suggest adding a description of "Support lookups in a section name std::map with both std::string and StringRef" or something to that effect (I'd suggest this be the title, but it's too long probably, so the description will have to do).

Thanks for the review! I've left "heterogenous lookup" in the title because it is a concise term used often in the C++ community, but I realize some people may not be familiar with the concept. I expanded a bit in the PR description.