[llvm-bugs] [Bug 48979] New: Failure to optimize some 64-bit constants in -Oz

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=48979

            Bug ID: 48979
           Summary: Failure to optimize some 64-bit constants in -Oz
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Backend: X86
          Assignee: unassignedbugs at nondot.org
          Reporter: gabravier at gmail.com
                CC: craig.topper at gmail.com, llvm-bugs at lists.llvm.org,
                    llvm-dev at redking.me.uk, pengfei.wang at intel.com,
                    spatel+llvm at rotateright.com

int64_t f()
{
    return 0x1234567800000000;
}

With -Os, GCC emits this:

f():
  mov eax, 38177487
  sal rax, 35
  ret

Clang -Oz emits this:

f():
  movabs rax, 1311768464867721216
  ret

GCC saves 1 byte over LLVM here.

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