r245459 - According to i686 ABI, long double size on x86 is 12 bytes not 16 bytes.
Hal Finkel via cfe-commits
cfe-commits at lists.llvm.org
Sat Sep 19 03:33:50 PDT 2015
FYI: https://llvm.org/bugs/show_bug.cgi?id=24398 was just reopened pointing to a lack of resolution here.
-Hal
----- Original Message -----
> From: "Yaron Keren via cfe-commits" <cfe-commits at lists.llvm.org>
> To: "Martell Malone" <martellmalone at gmail.com>
> Cc: "Richard Smith" <richard at metafoo.co.uk>, "cfe-commits" <cfe-commits at lists.llvm.org>
> Sent: Friday, August 21, 2015 2:47:50 AM
> Subject: Re: r245459 - According to i686 ABI, long double size on x86 is 12 bytes not 16 bytes.
>
>
>
>
> The testcase from r245459 was not reverted and still in SVN.
>
>
>
>
>
> 2015-08-21 2:05 GMT+03:00 Martell Malone < martellmalone at gmail.com >
> :
>
>
>
>
>
> I feel very silly now.
> After testing the testcase again on svn it still works.
> It appears the OP was looking for this patch to go onto the 3.6
> branch and was applying my patch to that.
>
>
> I'll know in future to recheck the testcase afterwards myself in
> future.
>
>
> Apologies for the noise guys.
>
>
> Yaron I think the test case from r245459 would be useful to ensure it
> is never broken in the future?
>
> Would you be able to recommit the test case?
>
>
>
> Kind Regards
>
> Martell
>
>
>
>
>
>
>
> On Thu, Aug 20, 2015 at 3:57 PM, Martell Malone <
> martellmalone at gmail.com > wrote:
>
>
>
>
>
> There is no testcase for PR24398 nor the OP reporting the problem was
> actually solved. Martell?
> I'm just re-looking through it now.
>
>
> X86TargetInfo sets LongDoubleFormat =
> &llvm::APFloat::x87DoubleExtended;
> X86_64TargetInfo then sets LongDoubleWidth = LongDoubleAlign = 128 ;
> X86_32 TargetInfo then sets LongDoubleWidth = 96 ; LongDoubleAlign =
> 32 ;
>
>
> From this I can see that the patch I committed actually doesn't
> change anything but only breaks mingw x86.
>
>
> I can only see these values changed in Microsoft*TargetInfo classes
> which is not a parent of MINGW
>
>
> When I submitted the patch I just wanted to explicitly set the values
> in MinGWX86_64TargetInfo to ensure it was in fact that.
>
> It seemed as though it was not inheriting the value from the root
> parent class somehow.
>
>
>
> I was told on irc that it did fix the bug which is even stranger.
> I'm actually at a bit of a loss as to what the proper fix to this is
> then.
>
> Apologies for breaking mingw i686 long double.
>
>
> I will do up a test case and try to find the actual cause of the long
> double bug and reopen the issue.
>
>
>
>
>
> On Thu, Aug 20, 2015 at 3:09 PM, Yaron Keren < yaron.keren at gmail.com
> > wrote:
>
>
>
>
> Hi, I've just done this exactly this in r245618 (32 bit) and r245620
> (64 bits).
>
>
> mingw i686 long double values were correct before r245084 and wrong
> after it.
> mingw x86_64 long double values were not modified at all by r245084
> for the reason you stated, so I agree and do not see how this
> non-change can solve anything . There is no testcase for PR24398 nor
> the OP reporting the problem was actually solved. Martell?
>
>
> About PR24398, long double support was in clang long ago and b oth
> code examples compile and run correctly with current svn (without
> r245084) and gcc version 5.1.0 (i686-posix-dwarf-rev0, Built by
> MinGW-W64 project).
> It's not x86_64 but as said r245084 didn't actually modify x86_64
> configuration.
>
>
>
>
>
>
>
>
>
>
>
> 2015-08-21 0:52 GMT+03:00 Richard Smith < richard at metafoo.co.uk > :
>
>
> OK, so here's the problem:
>
>
> The right way to fix this seems to be to delete the assignments to
> LongDouble* from the MinGWX86_32TargetInfo constructor; the
> X86_32TargetInfo and X86TargetInfo base classes already set them to
> the right values. Likewise we can delete the assignments to
> LongDouble* from the MinGWX86_64TargetInfo constructor for the same
> reason.
>
>
> But... that completely reverts Martell's r245084, which apparently
> fixed PR24398. So you two need to figure out what the actual problem
> is here, and what the right fix is. r245084 didn't provide any test
> cases, and had no apparent effect other than to break long double
> for mingw32; did it really fix PR24398 (and if so, how)?
>
>
>
>
>
> On Thu, Aug 20, 2015 at 2:27 PM, Yaron Keren < yaron.keren at gmail.com
> > wrote:
>
>
>
>
> OK, based on testing, mingw i686 aligns long doubles to 4 bytes:
>
>
>
>
> sh-4.3$ cat < a.cpp
> #include <iostream>
> int main() {
> struct {
> char c[1];
> long double d;
> } s;
> std::cout<<&s.c<<std::endl;
> std::cout<<&s.d<<std::endl;
> }
> sh-4.3$ g++ a.cpp&&./a.exe
> 0x28fea0
> 0x28fea4
>
>
> I'll fix that.
>
>
>
>
>
>
>
> 2015-08-21 0:13 GMT+03:00 Richard Smith < richard at metafoo.co.uk > :
>
>
>
>
>
>
> On Wed, Aug 19, 2015 at 11:42 AM, Yaron Keren < yaron.keren at gmail.com
> > wrote:
>
>
>
>
> Yes, it looks like a legacy issue. Documentation says so:
>
>
>
> https://gcc.gnu.org/onlinedocs/gcc-4.8.2/gcc/i386-and-x86-64-Options.html
>
>
>
> -m96bit-long-double -m128bit-long-double These switches control the
> size of long double type. The i386 application binary interface
> specifies the size to be 96 bits, so -m96bit-long-double is the
> default in 32-bit mode.
>
> Modern architectures (Pentium and newer) prefer long double to be
> aligned to an 8- or 16-byte boundary. In arrays or structures
> conforming to the ABI, this is not possible. So specifying
> -m128bit-long-double aligns long double to a 16-byte boundary by
> padding the long double with an additional 32-bit zero.
>
> In the x86-64 compiler, -m128bit-long-double is the default choice as
> its ABI specifies that long double is aligned on 16-byte boundary.
>
> Notice that neither of these options enable any extra precision over
> the x87 standard of 80 bits for a long double .
>
> Warning: if you override the default value for your target ABI, this
> changes the size of structures and arrays containing long double
> variables, as well as modifying the function calling convention for
> functions taking long double . Hence they are not binary-compatible
> with code compiled without that switch.
>
>
> And practical testing agrees:
>
>
>
>
> sh-4.3$ cat < a.cpp
> #include <iostream>
> int main() {
> long double a;
> std::cout<<sizeof(a)<<std::endl;
> }
> sh-4.3$ g++ -v
> Using built-in specs.
> COLLECT_GCC=C:\mingw32\bin\g++.exe
> COLLECT_LTO_WRAPPER=C:/mingw32/bin/../libexec/gcc/i686-w64-mingw32/5.1.0/lto-wrapper.exe
> Target: i686-w64-mingw32
> Configured with: ../../../src/gcc-5.1.0/configure
> --host=i686-w64-mingw32 --build=i686-w64-mingw32
> --target=i686-w64-mingw32 --prefix=/mingw32
> --with-sysroot=/c/mingw510/i686-510-posix-dwarf-rt_v4-rev0/mingw32
> --with-gxx-include-dir=/mingw32/i686-w64-mingw32/include/c++
> --enable-shared --enable-static --disable-multilib
> --enable-languages=c,c++,fortran,objc,obj-c++,lto
> --enable-libstdcxx-time=yes --enable-threads=posix --enable-libgomp
> --enable-libatomic --enable-lto --enable-graphite
> --enable-checking=release --enable-fully-dynamic-string
> --enable-version-specific-runtime-libs --disable-sjlj-exceptions
> --with-dwarf2 --disable-isl-version-check --disable-libstdcxx-pch
> --disable-libstdcxx-debug --enable-bootstrap --disable-rpath
> --disable-win32-registry --disable-nls --disable-werror
> --disable-symvers --with-gnu-as --with-gnu-ld --with-arch=i686
> --with-tune=generic --with-libiconv --with-system-zlib
> --with-gmp=/c/mingw510/prerequisites/i686-w64-mingw32-static
> --with-mpfr=/c/mingw510/prerequisites/i686-w64-mingw32-static
> --with-mpc=/c/mingw510/prerequisites/i686-w64-mingw32-static
> --with-isl=/c/mingw510/prerequisites/i686-w64-mingw32-static
> --with-pkgversion='i686-posix-dwarf-rev0, Built by MinGW-W64
> project' --with-bugurl= http://sourceforge.net/projects/mingw-w64
> CFLAGS='-O2 -pipe
> -I/c/mingw510/i686-510-posix-dwarf-rt_v4-rev0/mingw32/opt/include
> -I/c/mingw510/prerequisites/i686-zlib-static/include
> -I/c/mingw510/prerequisites/i686-w64-mingw32-static/include'
> CXXFLAGS='-O2 -pipe
> -I/c/mingw510/i686-510-posix-dwarf-rt_v4-rev0/mingw32/opt/include
> -I/c/mingw510/prerequisites/i686-zlib-static/include
> -I/c/mingw510/prerequisites/i686-w64-mingw32-static/include'
> CPPFLAGS= LDFLAGS='-pipe
> -L/c/mingw510/i686-510-posix-dwarf-rt_v4-rev0/mingw32/opt/lib
> -L/c/mingw510/prerequisites/i686-zlib-static/lib
> -L/c/mingw510/prerequisites/i686-w64-mingw32-static/lib
> -Wl,--large-address-aware'
> Thread model: posix
> gcc version 5.1.0 (i686-posix-dwarf-rev0, Built by MinGW-W64 project)
>
>
> sh-4.3$ g++ a.cpp
> sh-4.3$ ./a.exe
>
> 12
>
>
> Without the patch clang outputs 16 and seg faults on a boost::math
> example.
>
>
> None of that answers my question. Our default GCC-compatible behavior
> for x86_32 long double is to give it 4-byte alignment, 12-byte size,
> and this matches the behavior I observe with GCC. Does MinGW
> /really/ deviate from this and give long double a 16-byte alignment?
>
>
>
>
>
>
>
>
>
>
> 2015-08-19 21:29 GMT+03:00 Richard Smith < richard at metafoo.co.uk > :
>
>
>
>
>
>
> On Wed, Aug 19, 2015 at 10:02 AM, Yaron Keren via cfe-commits <
> cfe-commits at lists.llvm.org > wrote:
>
>
> Author: yrnkrn
> Date: Wed Aug 19 12:02:32 2015
> New Revision: 245459
>
> URL: http://llvm.org/viewvc/llvm-project?rev=245459&view=rev
> Log:
> According to i686 ABI, long double size on x86 is 12 bytes not 16
> bytes.
> See
> https://gcc.gnu.org/onlinedocs/gcc-3.2/gcc/i386-and-x86-64-Options.html
>
>
> Added:
> cfe/trunk/test/CodeGen/mingw-long-double-size.c
> Modified:
> cfe/trunk/lib/Basic/Targets.cpp
>
> Modified: cfe/trunk/lib/Basic/Targets.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Basic/Targets.cpp?rev=245459&r1=245458&r2=245459&view=diff
> ==============================================================================
> --- cfe/trunk/lib/Basic/Targets.cpp (original)
> +++ cfe/trunk/lib/Basic/Targets.cpp Wed Aug 19 12:02:32 2015
> @@ -3785,7 +3785,8 @@ class MinGWX86_32TargetInfo : public Win
> public:
> MinGWX86_32TargetInfo(const llvm::Triple &Triple)
> : WindowsX86_32TargetInfo(Triple) {
> - LongDoubleWidth = LongDoubleAlign = 128;
> + LongDoubleWidth = 96;
> + LongDoubleAlign = 128;
>
>
>
> Is this really correct? It's deeply suspicious that the size is not a
> multiple of the alignment.
>
>
> LongDoubleFormat = &llvm::APFloat::x87DoubleExtended;
> }
> void getTargetDefines(const LangOptions &Opts,
>
> Added: cfe/trunk/test/CodeGen/mingw-long-double-size.c
> URL:
> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGen/mingw-long-double-size.c?rev=245459&view=auto
> ==============================================================================
> --- cfe/trunk/test/CodeGen/mingw-long-double-size.c (added)
> +++ cfe/trunk/test/CodeGen/mingw-long-double-size.c Wed Aug 19
> 12:02:32 2015
> @@ -0,0 +1,5 @@
> +// RUN: %clang_cc1 -triple i686-pc-windows-gnu -S %s -o - |
> FileCheck %s -check-prefix=CHECK_I686
> +// CHECK_I686: lda,12
> +// RUN: %clang_cc1 -triple x86_64-pc-windows-gnu -S %s -o - |
> FileCheck %s -check-prefix=CHECK_X86_64
> +// CHECK_X86_64: lda,16
> +long double lda;
>
>
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--
Hal Finkel
Assistant Computational Scientist
Leadership Computing Facility
Argonne National Laboratory
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