Wrong optimizr code generation

[ElijahGr]

Expression (ival = ( int) val) is executed even if safeCast==false

example for this issue: d.cpp

#include <stdio.h>
#include <limits.h>

double nextVal()
{
  static double vals[4]={1, 2, 70203888290798.0, 4};
  static int index;
  index &= 3;
  return vals[index++];
}

void test()
{
  double val = nextVal();
  printf("test %f ", val);
  int ival = 0;
  bool safeCast = (val>=INT_MIN && val<=INT_MAX);
  printf("cast %d ", safeCast);

  if (safeCast)
  {
    ival = ( int) val; //code is always executed even if safeCast==false
  }

  if ((double)ival == val)
  {
    printf("val %f is int\n", val);
    return;
  }
  printf("%f not int\n", val);
}

int main()
{
  test();
  test();
  test(); //raise integer overflow error 
  test();
}

Compile command:
emcc -O2 d.cpp -o d.html -s WASM=1

This error not appears without any optimization or BINARYEN_TRAP_MODE='clamp'.
Looks like the compiler believe that expression (ival = ( int) val) has no side effects this is not the case.

[kripken]

This looks like the same as WebAssembly/binaryen#1110 , where the LLVM optimizer can move code around in ways that can trap in wasm. (The binaryen optimizer is aware of this, but not the LLVM optimizer.)

This seems to be a common issue, maybe we need to think about a plan for this that includes all the compilers and optimizers.

[dschuff]

See also #5498

[stale]

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