v8/test/mjsunit/codegen-coverage.js

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// Test paths in the code generator where values in specific registers
// get moved around.
function identity(x) {
  return x;
}

function lookup(w, a) {
  // This function tests a code path in the generation of a keyed load IC
  // where the key and the value are both in the same register.
  a = a;
  w[a] = a;
}

function cover_codegen_paths() {
  var x = 1;

  // This test depends on the fixed order of register allocation.  We try to
  // get values in specific registers (ia32, x64):
  var a;   // Register eax, rax.
  var b;   // Register ebx, rbx.
  var c;   // Register ecx, rcx.
  var d;   // Register edx, rdx.
  var di;  // Register edi, rdi.

  while (x == 1) {
    // The call will spill registers and leave x in {eax,rax}.
    x = identity(1);
    // The add will spill x and reuse {eax,rax} for the result.
    a = x + 1;
    // A fresh register {ebx,rbx} will be allocated for x, then reused for
    // the result.
    b = x + 1;
    // Et cetera.
    c = x + 1;
    d = x + 1;
    di = x + 1;
    // Locals are in the corresponding registers here.
    assertEquals(8, c << a);

    x = identity(1);
    a = x + 1;
    b = x + 1;
    c = x + 1;
    d = x + 1;
    di = x + 1;
    assertEquals(8, a << c);

    x = identity(1);
    a = x + 1;
    b = x + 1;
    c = x + 1;
    d = x + 1;
    di = x + 1;
    c = 0; // Free register ecx.
    assertEquals(8, a << d);

    x = identity(1);
    a = x + 1;
    b = x + 1;
    c = x + 1;
    d = x + 1;
    di = x + 1;
    b = 0; // Free register ebx.
    assertEquals(8, a << d);

    // Test the non-commutative subtraction operation with a smi on the
    // left, all available registers on the right, and a non-smi result.
    x = identity(-1073741824);  // Least (31-bit) smi.
    a = x + 1;  // Still a smi, the greatest smi negated.
    b = x + 1;
    c = x + 1;
    d = x + 1;
    di = x + 1;
    // Subtraction should overflow the 31-bit smi range.  The result
    // (1073741824) is outside the 31-bit smi range so it doesn't hit the
    // "unsafe smi" code that spills a register.
    assertEquals(1073741824, 1 - a);

    x = identity(-1073741824);
    a = x + 1;
    b = x + 1;
    c = x + 1;
    d = x + 1;
    di = x + 1;
    assertEquals(1073741824, 1 - b);

    x = identity(-1073741824);
    a = x + 1;
    b = x + 1;
    c = x + 1;
    d = x + 1;
    di = x + 1;
    assertEquals(1073741824, 1 - c);

    x = identity(-1073741824);
    a = x + 1;
    b = x + 1;
    c = x + 1;
    d = x + 1;
    di = x + 1;
    assertEquals(1073741824, 1 - d);

    x = identity(-1073741824);
    a = x + 1;
    b = x + 1;
    c = x + 1;
    d = x + 1;
    di = x + 1;
    assertEquals(1073741824, 1 - di);

    x = 3;
    var w = { };
    lookup(w, x);
    lookup(w, x);
    lookup(w, x);

    x = 3;  // Terminate while loop.
  }
}

cover_codegen_paths();