[LLVMbugs] [Bug 8399] New: Incorrect sizeof(long double) on Windows.

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=8399

           Summary: Incorrect sizeof(long double) on Windows.
           Product: clang
           Version: trunk
          Platform: PC
        OS/Version: Windows NT
            Status: NEW
          Severity: normal
          Priority: P
         Component: LLVM Codegen
        AssignedTo: unassignedclangbugs at nondot.org
        ReportedBy: bigcheesegs at gmail.com
                CC: llvmbugs at cs.uiuc.edu


The Microsoft C/C++ ABI treats long double as 8 bytes instead of the 12 that
others use. Clang doesn't know about this.

Also the MSVC code seems slightly better. Reusing st(0) instead of duplicating
it. But that's for another PR.

=============================================================================
file: long-double.c
=============================================================================
#include <stdio.h>
int main(void) {
  long double x = 1.0;
  printf("%Lf %Lf\n", x, x);
  return sizeof(x);
}
=============================================================================

=============================================================================
compiler: clang
file: long-double.s
=============================================================================
    .def     _main;
    .scl    2;
    .type    32;
    .endef
    .text
    .globl    _main
    .align    16, 0x90
_main:                                  # @main
# BB#0:                                 # %entry
    pushl    %ebp
    movl    %esp, %ebp
    subl    $32, %esp
    fld1
    fld    %st(0)
    fstpt    16(%esp)
    fstpt    4(%esp)
    movl    $L_.str, (%esp)
    calll    _printf
    movl    $12, %eax
    addl    $32, %esp
    popl    %ebp
    ret

    .data
L_.str:                                 # @.str
    .asciz     "%Lf %Lf\n"


    .globl    __fltused
=============================================================================

=============================================================================
compiler: cl.exe included with Visual C++ 2010
file: long-double.asm
=============================================================================
; Listing generated by Microsoft (R) Optimizing Compiler Version 16.00.30319.01

    TITLE   
C:\Users\Michael\Projects\llvm\projects\test-suite\build\2008-01-07-LongDouble.c
    .686P
    .XMM
    include listing.inc
    .model    flat

INCLUDELIB LIBCMT
INCLUDELIB OLDNAMES

_DATA    SEGMENT
$SG2686    DB    '%Lf %Lf', 0aH, 00H
_DATA    ENDS
PUBLIC    __real at 3ff0000000000000
PUBLIC    _main
EXTRN    _printf:PROC
EXTRN    __fltused:DWORD
;    COMDAT __real at 3ff0000000000000
; File
c:\users\michael\projects\llvm\projects\test-suite\build\2008-01-07-longdouble.c
CONST    SEGMENT
__real at 3ff0000000000000 DQ 03ff0000000000000r    ; 1
; Function compile flags: /Ogtpy
CONST    ENDS
_TEXT    SEGMENT
_main    PROC
; Line 4
    fld1
    sub    esp, 16                    ; 00000010H
    fst    QWORD PTR [esp+8]
    fstp    QWORD PTR [esp]
    push    OFFSET $SG2686
    call    _printf
    add    esp, 20                    ; 00000014H
; Line 5
    mov    eax, 8
; Line 6
    ret    0
_main    ENDP
_TEXT    ENDS
END
=============================================================================

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