Stage2: Stack overflow iterating over large array

[jeffkdev]

Zig Version

0.10.0-dev.3659+e5e6eb983

Steps to Reproduce

Running this code on stage 2 will fail with a stack overflow. Runs correctly without errors on stage 1. I was able to reproduce in with zig run example.zig (Windows).

const MaxParticles: u32 = 512 * 2048;
var pos: [MaxParticles]Vec3 = .{Vec3{}} ** MaxParticles;
var vel: [MaxParticles]Vec3 =  .{Vec3{}} ** MaxParticles;

pub const Vec3 = struct {
    x: f32 = 0,
    y: f32 = 0,
    z: f32 = 0,
};

pub fn main() void {
    const cur_num_particles = 10;
    var i: u32 = 0;
    while (i < cur_num_particles) : (i += 1) {
        vel[i].y -= 1.0;
        pos[i].x += vel[i].x;
        pos[i].y += vel[i].y;
        pos[i].z += vel[i].z;
    }
}

Refactoring the while loop will allow it to run correctly:

    while (i < cur_num_particles) : (i += 1) {
        const particle_pos = &pos[i];
        const particle_vel = &vel[i];
        particle_vel.y -= 1.0;
        particle_pos.x += particle_vel.x;
        particle_pos.y += particle_vel.y;
        particle_pos.z += particle_vel.z;
    }

Also changing MaxParticles to smaller number will allow stage 2 to run it:

const MaxParticles: u32 = 512;

Expected Behavior

Runs and exits without errors

Actual Behavior

Stack overflow.

• VSCode DebuggerException has occurred: W32/0xC00000FD Exception thrown at 0x00007FF7D9A185C6 in program.exe: 0xC00000FD: Stack overflow (parameters: 0x0000000000000000, 0x0000001469A03760).
• Command line output from zig run: Stack Overflow

[Vexu]

This looks like a duplicate of #12215

[Vexu]

Confirmed duplicate, main allocas 3 * 3 * 1MiB.

  %1 = alloca [1048576 x %a.Vec3], align 4
  %2 = alloca [1048576 x %a.Vec3], align 4
  %3 = alloca [1048576 x %a.Vec3], align 4