llvm dev - Jul 2016 - Simple program fails to compile depending on target os

Hi *,

in the process of improving the ios experience with ghc, I ran into the
following issue:
the produced llvm code[1] compiles for `armv7-apple-darwin`, unless optimization
level is 0,
however it fails to compile at all for `armv7-apple-ios`.

I was able to reduce the produced code, while retaining the compilation issue on
`armv7-apple-ios`
to the following sample case:

————————————————————— 8< —————————————————————
define ghccc void @"f$def"(i32* noalias nocapture %Base_Arg,
                           i32* noalias nocapture %Sp_Arg,
                           i32* noalias nocapture %Hp_Arg,
                           i32 %R1_Arg, i32 %R2_Arg, i32 %R3_Arg, i32 %R4_Arg,
                           i32 %SpLim_Arg,
                           float %F1_Arg, float %F2_Arg, float %F3_Arg, float
%F4_Arg,
                           double %D1_Arg, double %D2_Arg) #0
                           align 4 prefix <{ i32, i32 }> <{ i32 1, i32
37 }> {

  %someElem = getelementptr inbounds i32, i32* %Base_Arg, i32 203
  
  %someValue = load i32, i32* %someElem
  %somePtr = inttoptr i32 %someValue to void (i32*, i32*, i32*, i32, i32, i32,
i32, i32, float, float, float, float, double, double)*
  tail call ghccc void %somePtr(i32* %Base_Arg,
                                i32* %Sp_Arg,
                                i32* %Hp_Arg,
                                i32 %R1_Arg, i32 %R2_Arg, i32 %R3_Arg, i32
%R4_Arg,
                                i32 %SpLim_Arg,
                                float %F1_Arg, float %F2_Arg, float %F3_Arg,
float %F4_Arg,
                                double %D1_Arg, double %D2_Arg) #0
  ret void
}

attributes #0 = { nounwind }
————————————————————— 8< —————————————————————

$ llc sample.ll -mtriple=armv7-apple-darwin # succeeds for 3.7 and 3.8
$ llc sample.ll -mtriple=armv7-apple-ios    # fails    for 3.7 and 3.8


Any hints as to why this code only compiles for darwin and not for ios, would be
greatly appreciated.

Cheers,
 Moritz

[1]: http://lpaste.net/1177160917046001664

On 3 July 2016 at 18:26, Moritz Angermann via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> Any hints as to why this code only compiles for darwin and not for ios,
would be greatly appreciated.
I saw the same thing on a checkout from a few months back, but I then
updated and ToT seems to get it right (well, slightly different
CodeGen because the iOS linker only started supporting tail calls at
5.0 or something so -darwin doesn't use them, but both compiled to
correct code). There's certainly been some churn in this bit of code
recently, so the bug was probably fixed incidentally as part of that.

Tim.

Thanks!

I also found test/CodeGen/ARM/ghc-tcreturn-lowered.ll, which tests only for
thumbv7-eabi,
so, i tried a few more variations:

[x] arm64-apple-ios
[x] arm64-apple-ios7.0.0
[x] arm64-apple-darwin
[x] armv7-apple
[x] thumbv7-apple
[x] thumbv7-apple-darwin
[x] i386-apple-ios
[x] i386-apple-darwin

[f] thumbv7-apple-ios
[f] thumbv7-apple-ios7.0.0
[f] armv7-apple-ios

I’ve also just build a HEAD version (LLVM version 3.9.0svn), and the code in
fact *does*
compile with 3.9.0svn.

Cheers,
 Moritz
> On Jul 4, 2016, at 10:19 AM, Tim Northover <t.p.northover at
gmail.com> wrote:
> 
> On 3 July 2016 at 18:26, Moritz Angermann via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
>> Any hints as to why this code only compiles for darwin and not for ios,
would be greatly appreciated.
> 
> I saw the same thing on a checkout from a few months back, but I then
> updated and ToT seems to get it right (well, slightly different
> CodeGen because the iOS linker only started supporting tail calls at
> 5.0 or something so -darwin doesn't use them, but both compiled to
> correct code). There's certainly been some churn in this bit of code
> recently, so the bug was probably fixed incidentally as part of that.
> 
> Tim.