Fix for the crash from #6367 (#6375)

* Skip empty boxes

* Address the comments

(cherry picked from commit 5b8f473)

src/BoundsInference.cpp

@@ -1133,7 +1133,10 @@ class BoundsInference : public IRMutator {
                 auto boxes = boxes_provided(body, empty_scope, func_bounds);
                 for (const auto &fused : fused_group) {
                     string fused_stage_name = fused.first + ".s" + std::to_string(fused.second);
-                    boxes_for_fused_group[fused_stage_name] = boxes[fused.first];
+                    auto it = boxes.find(fused.first);
+                    if (it != boxes.end()) {
+                        boxes_for_fused_group[fused_stage_name] = it->second;
+                    }
                     for (const auto &fn : funcs) {
                         if (fn.name() == fused.first) {
                             stage_name_to_func[fused_stage_name] = fn;

test/correctness/compute_with.cpp

@@ -2110,6 +2110,93 @@ int rvar_bounds_test() {
     return 0;
 }
 
+// Test for the issue described in https://github.com/halide/Halide/issues/6367.
+int two_compute_at_test() {
+    ImageParam input1(Int(16), 2, "input1");
+    Func output1("output1"), output2("output2"), output3("output3");
+    Var k{"k"};
+
+    Func intermediate{"intermediate"};
+    Func output1_value{"output1_value"};
+    Func output3_value{"output3_value"};
+
+    intermediate(k) = input1(k, 0) * input1(k, 1);
+    output1_value(k) = intermediate(k) * intermediate(k);
+    output1(k) = output1_value(k);
+    output2(k) = output1_value(k) + output1_value(k);
+    output3_value(k) = input1(k, 0) + 2;
+    output3(k) = output3_value(k);
+
+    Expr num = input1.dim(0).extent();
+    input1.dim(0).set_bounds(0, num);
+    input1.dim(1).set_bounds(0, 2);
+    output1.output_buffer().dim(0).set_bounds(0, num);
+    output2.output_buffer().dim(0).set_bounds(0, num);
+    output3.output_buffer().dim(0).set_bounds(0, num);
+
+    intermediate
+        .vectorize(k, 8)
+        .compute_at(output1_value, k)
+        .bound_storage(k, 8)
+        .store_in(MemoryType::Register);
+
+    output1_value
+        .vectorize(k, 8)
+        .compute_at(output2, k)
+        .bound_storage(k, 8)
+        .store_in(MemoryType::Register);
+
+    output1
+        .vectorize(k, 8)
+        .compute_with(output2, k);
+
+    output2
+        .vectorize(k, 8);
+
+    output3_value
+        .vectorize(k, 8)
+        .compute_at(output3, k)
+        .bound_storage(k, 8)
+        .store_in(MemoryType::Register);
+
+    output3
+        .vectorize(k, 8)
+        .compute_with(output2, k);
+
+    Pipeline p({output1, output2, output3});
+    p.compile_jit();
+
+    Buffer<int16_t> in(8, 2);
+    Buffer<int16_t> o1(8), o2(8), o3(8);
+    for (int iy = 0; iy < in.height(); iy++) {
+        for (int ix = 0; ix < in.width(); ix++) {
+            in(ix, iy) = ix + iy;
+        }
+    }
+    input1.set(in);
+    p.realize({o1, o2, o3});
+
+    for (int x = 0; x < 8; x++) {
+        int val = (x * (x + 1)) * (x * (x + 1));
+        if (o1(x) != val) {
+            printf("o1(%d) = %d instead of %d\n",
+                   x, o1(x), val);
+            return -1;
+        }
+        if (o2(x) != 2 * val) {
+            printf("o2(%d) = %d instead of %d\n",
+                   x, o2(x), 2 * val);
+            return -1;
+        }
+        if (o3(x) != x + 2) {
+            printf("o2(%d) = %d instead of %d\n",
+                   x, o3(x), x + 2);
+            return -1;
+        }
+    }
+    return 0;
+}
+
 }  // namespace
 
 int main(int argc, char **argv) {
@@ -2256,6 +2343,11 @@ int main(int argc, char **argv) {
         return -1;
     }
 
+    printf("Running two_compute_at test\n");
+    if (two_compute_at_test() != 0) {
+        return -1;
+    }
+
     printf("Success!\n");
     return 0;
 }