Facilities to stop NaN propagation in FPU programs

[kv-sc]

Reproduce on 1.0

snippy command line:

./llvm-snippy -march=riscv64-linux-gnu -mattr="+f,+d" -reserved-regs-list="F0_D,F1_D,F2_D,F3_D,F4_D,F5_D,F6_D,F7_D,F8_D,F9_D,F13_D,F14_D,F15_D,F16_D,F17_D,F18_D,F19_D,F20_D,F21_D,F22_D,F23_D,F24_D,F25_D,F26_D,F27_D,F28_D,F29_D,F30_D,F31_D,X3,X4" -num-instrs=1000 -seed=0 -model-plugin=None ./layout-stack.yaml --init-regs-in-elf -last-instr=RET --honor-target-abi --external-stack

where layout-stack.yaml looks like:

sections:
  - no:        0
    VMA:       0x200000
    SIZE:      0x10000
    LMA:       0x200000
    ACCESS:    r
  - no:        1
    VMA:       0x210000
    SIZE:      0x100000
    LMA:       0x210000
    ACCESS:    rx
  - no:        2
    VMA:       0x400000
    SIZE:      0x100000
    LMA:       0x400000
    ACCESS:    rw

call-graph:
  entry-point: SnippyFunction
  function-list:
    - name: SnippyFunction
      callees:
        - myfunc
    - name: myfunc
      external: true

histogram:
     - [FADD_D, 3.0]
     - [FDIV_D, 3.0]
     - [FMUL_D, 3.0]
     - [FSUB_D, 3.0]
     - [JAL, 1.0]

file myfunc.c:

#include <stdio.h>

void SnippyFunction();

int main() {
  SnippyFunction();
}

void myfunc(double a, double b, double c) {
  printf("%lf, %lf, %lf\n", a, b, c);
}

Link:

riscv64-unknown-linux-gnu-gcc layout-stack.yaml.elf myfunc.c --static

Run:

qemu-riscv64 ./a.out

You will see all NaN's from some moment:

0.000000, 40218038886127496574296745899399669469321707570122526914569185871875156215437721600.000000, -138045858897988964649892385629183438148452756182408624093268872718730204601415295754909095360179370021264444269979234186020103682241025079447796987457768435325337600.000000
-138045858897988964649892385629183438148452756182408624093268872718730204601415295754909095360179370021264444269979234186020103682241025079447796987457768435325337600.000000, 40218038886127496574296745899399669469321707570122526914569185871875156215437721600.000000, -138045858897988964649892385629183438148452756182408624093268872718730204601415295754909095360179370021264444269979234186020103682241025079447796987457768435325337600.000000
0.000000, -5551933721228190040891410660573517160096470692414526918920611429325881414518518172311287619687182300040152711520452995236828182756607735946804109994190053157736295687726783280742427698719907518737640118245085691142791819310348625796764153805799424.000000, 1.000000
1.000000, 1.000000, -0.000000
nan, nan, nan
nan, nan, nan
nan, nan, nan
nan, nan, nan
nan, nan, nan
nan, nan, nan
nan, nan, nan
nan, nan, nan
nan, nan, nan
nan, nan, nan
nan, nan, nan
nan, nan, nan
nan, nan, nan
....