[llvm-bugs] [Bug 30317] New: Constructing a vector with an initializer list generates more code than push_back / emplace_back

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=30317

            Bug ID: 30317
           Summary: Constructing a vector with an initializer list
                    generates more code than push_back / emplace_back
           Product: clang
           Version: unspecified
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: normal
          Priority: P
         Component: LLVM Codegen
          Assignee: unassignedclangbugs at nondot.org
          Reporter: dcheng at google.com
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

Simple test case:

#include <stdio.h>

#include <string>
#include <vector>

void PrintVector(const std::vector<std::string>& strings) {
  for (const auto& s : strings) {
    printf("%s\n", s.data());
  }
}

void Foo() {
  std::vector<std::string> names;
  names.push_back("abc");
  names.push_back("def");
  names.push_back("ghi");
  PrintVector(names);
}

void Bar() {
  std::vector<std::string> names{
    "abc",
    "def",
    "ghi",
  };
  PrintVector(names);
}

int main() {
  Foo();
  Bar();
}

With -O2, the function sizes are roughly the same. Foo() is 847 bytes, Bar() is
844 bytes.
With -O1, Foo() is much smaller at 294 bytes, while Bar() is 396 bytes.

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