[LLVMbugs] [Bug 6799] New: clang -O2 emits wrong asm

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Tue Apr 6 15:51:06 CDT 2010


http://llvm.org/bugs/show_bug.cgi?id=6799

           Summary: clang -O2 emits wrong asm
           Product: clang
           Version: unspecified
          Platform: PC
        OS/Version: FreeBSD
            Status: NEW
          Severity: normal
          Priority: P
         Component: LLVM Codegen
        AssignedTo: unassignedclangbugs at nondot.org
        ReportedBy: rdivacky at freebsd.org
                CC: llvmbugs at cs.uiuc.edu


when compiling the attached gcc produces this code:

gcc -S -O2 tree1.c:
getcnode:
.LFB6:
        movq    %rbx, -24(%rsp)
.LCFI0:
        movq    %r12, -16(%rsp)
.LCFI1:
        movq    %rsi, %r12
        movq    %r13, -8(%rsp)
.LCFI2:
        subq    $24, %rsp
.LCFI3:
        movq    %rdi, %r13
        call    getnode
        movl    $32, %edi
        movq    %rax, %rbx
        movq    %r13, 8(%rax)
        movl    $47, (%rax)
        call    tgetblk
        movq    %rax, 24(%rbx)
        movl    (%r13), %edx
        movq    %r12, %rdi
        movl    %edx, (%rax)
        movl    4(%r12), %eax
        movq    24(%rbx), %rdx
        movl    %eax, 4(%rdx)
        movq    16(%r12), %rax
        movq    24(%rbx), %rdx
        movq    %rax, 16(%rdx)
        movq    24(%r12), %rax              (1)
        movq    %rax, 24(%rdx)              (2)
        call    free
        movq    %rbx, %rax
        movq    8(%rsp), %r12
        movq    (%rsp), %rbx
        movq    16(%rsp), %r13
        addq    $24, %rsp
        ret

while clang -S -O2 tree1.c:

getcnode:
.Leh_func_begin1:
        pushq   %rbp
.Ltmp0:
        movq    %rsp, %rbp
.Ltmp1:
        pushq   %r15
        pushq   %r14
        pushq   %rbx
        subq    $8, %rsp
.Ltmp2:
        movq    %rsi, %rbx
        movq    %rdi, %r14
        callq   getnode
        movq    %rax, %r15
        movl    $47, (%r15)
        movq    %r14, 8(%r15)
        movl    $32, %edi
        callq   tgetblk
        movq    %rax, 24(%r15)
        movl    (%r14), %ecx
        movl    %ecx, (%rax)
        movq    24(%r15), %rax
        movl    4(%rbx), %ecx
        movl    %ecx, 4(%rax)
        movq    24(%r15), %rax
        movaps  16(%rbx), %xmm0           (3)
        movaps  %xmm0, 16(%rax)           (4)
        movq    %rbx, %rdi
        callq   free
        movq    %r15, %rax
        addq    $8, %rsp
        popq    %rbx
        popq    %r14
        popq    %r15
        popq    %rbp
        ret

note that the offset for (1) and (2) is 24 for gcc while 16 for clang at (3)
and (4), this makes "lint" crash

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