[llvm-commits] [llvm] r168704 - in /llvm/trunk: lib/CodeGen/AsmPrinter/AsmPrinter.cpp test/CodeGen/ARM/2010-12-15-elf-lcomm.ll test/CodeGen/ARM/elf-lcomm-align.ll

[Rafael Espíndola]

Any reason why the integrated assembler should not implement lcomm the
same way as the external assembler?

On 27 November 2012 11:11, Ulrich Weigand <ulrich.weigand at de.ibm.com> wrote:
> Author: uweigand
> Date: Tue Nov 27 10:11:16 2012
> New Revision: 168704
>
> URL: http://llvm.org/viewvc/llvm-project?rev=168704&view=rev
> Log:
> Never use .lcomm on platforms where it does not accept an alignment
> argument.  Instead, use a pair of .local and .comm directives.
>
> This avoids spurious differences between binaries built by the
> integrated assembler vs. those built by the external assembler,
> since the external assembler may impose alignment requirements
> on .lcomm symbols where the integrated assembler does not.
>
> Modified:
>     llvm/trunk/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
>     llvm/trunk/test/CodeGen/ARM/2010-12-15-elf-lcomm.ll
>     llvm/trunk/test/CodeGen/ARM/elf-lcomm-align.ll
>
> Modified: llvm/trunk/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/AsmPrinter/AsmPrinter.cpp?rev=168704&r1=168703&r2=168704&view=diff
> ==============================================================================
> --- llvm/trunk/lib/CodeGen/AsmPrinter/AsmPrinter.cpp (original)
> +++ llvm/trunk/lib/CodeGen/AsmPrinter/AsmPrinter.cpp Tue Nov 27 10:11:16 2012
> @@ -308,8 +308,13 @@
>        return;
>      }
>
> -    if (Align == 1 ||
> -        MAI->getLCOMMDirectiveAlignmentType() != LCOMM::NoAlignment) {
> +    // Use .lcomm only if it supports user-specified alignment.
> +    // Otherwise, while it would still be correct to use .lcomm in some
> +    // cases (e.g. when Align == 1), the external assembler might enfore
> +    // some -unknown- default alignment behavior, which could cause
> +    // spurious differences between external and integrated assembler.
> +    // Prefer to simply fall back to .local / .comm in this case.
> +    if (MAI->getLCOMMDirectiveAlignmentType() != LCOMM::NoAlignment) {
>        // .lcomm _foo, 42
>        OutStreamer.EmitLocalCommonSymbol(GVSym, Size, Align);
>        return;
>
> Modified: llvm/trunk/test/CodeGen/ARM/2010-12-15-elf-lcomm.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/ARM/2010-12-15-elf-lcomm.ll?rev=168704&r1=168703&r2=168704&view=diff
> ==============================================================================
> --- llvm/trunk/test/CodeGen/ARM/2010-12-15-elf-lcomm.ll (original)
> +++ llvm/trunk/test/CodeGen/ARM/2010-12-15-elf-lcomm.ll Tue Nov 27 10:11:16 2012
> @@ -10,7 +10,8 @@
>  @STRIDE = internal global i32 8
>
>  ; ASM:          .type   array00,%object         @ @array00
> -; ASM-NEXT:     .lcomm  array00,80
> +; ASM-NEXT:     .local  array00
> +; ASM-NEXT:     .comm   array00,80,1
>  ; ASM-NEXT:     .type   _MergedGlobals,%object  @ @_MergedGlobals
>
>
>
> Modified: llvm/trunk/test/CodeGen/ARM/elf-lcomm-align.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/ARM/elf-lcomm-align.ll?rev=168704&r1=168703&r2=168704&view=diff
> ==============================================================================
> --- llvm/trunk/test/CodeGen/ARM/elf-lcomm-align.ll (original)
> +++ llvm/trunk/test/CodeGen/ARM/elf-lcomm-align.ll Tue Nov 27 10:11:16 2012
> @@ -4,8 +4,9 @@
>  @c = internal global i8 0, align 1
>  @x = internal global i32 0, align 4
>
> -; CHECK: .lcomm c,1
> -; .lcomm doesn't support alignment.
> +; .lcomm doesn't support alignment, so we always use .local/.comm.
> +; CHECK: .local c
> +; CHECK-NEXT: .comm c,1,1
>  ; CHECK: .local x
>  ; CHECK-NEXT: .comm x,4,4
>
>
>
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