[Mono-dev] Question regarding compiler optimizations causing floating point failure on Arm

[Koushik K. Dutta]

Hi, I am building Mono/Arm under the Android build environment. The Android build environment uses various gcc architecture and optimizations flags which I detail at the bottom of this mail.

If I use the default flags of their build system, the following C# program has some very interesting/buggy results with regard to floating point values!
public static class Program
{
      public static int Main(string[] args)
      {
            float num = 1.0f;
            Console.WriteLine(num); // this prints 2.561887???!
            return 0;
      }
}

But if in my Android.mk (Android build's makefile), I use the "-O0" flag (turn off all optimizations), the program displays "1" as expected.

Does anyone have any thoughts/ideas as to why this is happening?

I have tried using ARM_FPU_VFP, ARM_FPU_NONE, and ARM_FPU_FPA.

Default Android "Release" Flags:
my @compile_args = (
    "-march=armv5te",
    "-mtune=xscale",
    "-msoft-float",
    "-mthumb-interwork",
    "-fpic",
    "-fno-exceptions",
    "-ffunction-sections",
    "-funwind-tables", # static exception-like tables
    "-fstack-protector", # check guard variable before return
    "-fmessage-length=0"); # No line length limit to error messages

my @optimize_args = (
    "-O2",
    "-finline-functions",
    "-finline-limit=300",
    "-fno-inline-functions-called-once",
    "-fgcse-after-reload",
    "-frerun-cse-after-loop", # Implicit in -O2 per texinfo
    "-frename-registers",
    "-fomit-frame-pointer",
    "-fstrict-aliasing", # Implicit in -O2 per texinfo
    "-funswitch-loops");


Koushik Dutta
www.koushikdutta.com<http://www.koushikdutta.com/>

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