<html>
    <head>
      <base href="https://bugs.llvm.org/">
    </head>
    <body><table border="1" cellspacing="0" cellpadding="8">
        <tr>
          <th>Bug ID</th>
          <td><a class="bz_bug_link 
          bz_status_NEW "
   title="NEW - Merge constant literals"
   href="https://bugs.llvm.org/show_bug.cgi?id=43445">43445</a>
          </td>
        </tr>

        <tr>
          <th>Summary</th>
          <td>Merge constant literals
          </td>
        </tr>

        <tr>
          <th>Product</th>
          <td>clang
          </td>
        </tr>

        <tr>
          <th>Version</th>
          <td>trunk
          </td>
        </tr>

        <tr>
          <th>Hardware</th>
          <td>PC
          </td>
        </tr>

        <tr>
          <th>OS</th>
          <td>Linux
          </td>
        </tr>

        <tr>
          <th>Status</th>
          <td>NEW
          </td>
        </tr>

        <tr>
          <th>Severity</th>
          <td>enhancement
          </td>
        </tr>

        <tr>
          <th>Priority</th>
          <td>P
          </td>
        </tr>

        <tr>
          <th>Component</th>
          <td>LLVM Codegen
          </td>
        </tr>

        <tr>
          <th>Assignee</th>
          <td>unassignedclangbugs@nondot.org
          </td>
        </tr>

        <tr>
          <th>Reporter</th>
          <td>zamazan4ik@tut.by
          </td>
        </tr>

        <tr>
          <th>CC</th>
          <td>llvm-bugs@lists.llvm.org, neeilans@live.com, richard-llvm@metafoo.co.uk
          </td>
        </tr></table>
      <p>
        <div>
        <pre>Consider the example:

static const char data1[] = {'t','e','s','t'};
static const char data2[] = "test test";

bool index0(const char* cmp) {
    return cmp == data1 || cmp == data2;
}


Right now Clang(trunk) with 'std=c++17 -O3' generates suboptimal assembly:

index0(char const*): # @index0(char const*)
  mov eax, offset data1
  cmp rdi, rax
  sete cl
  mov eax, offset data2
  cmp rdi, rax
  sete al
  or al, cl
  ret
data1:
  .ascii "test"

data2:
  .asciz "test test"


A more efficient way to generate the code is to merge `data1` and `data2`:

index0(char const*):
  mov eax, offset data
  cmp rdi, rax
  sete al
  ret
data:
  .ascii "test test"


Constant literals merging significantly reduces binary size and cache misses.

Godbolt playground: <a href="https://godbolt.org/z/z-rJ6J">https://godbolt.org/z/z-rJ6J</a>

Related GCC issue: <a href="https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91899">https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91899</a></pre>
        </div>
      </p>


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