Don't deduce unreachability from predicated out of bounds stores (#7874)

Fixes #7873

src/Simplify_Stmts.cpp

@@ -300,12 +300,13 @@ Stmt Simplify::visit(const Store *op) {
     ExprInfo index_info;
     Expr index = mutate(op->index, &index_info);
 
-    // If the store is fully out of bounds, drop it.
+    // If the store is fully unconditional and out of bounds, drop it.
     // This should only occur inside branches that make the store unreachable,
     // but perhaps the branch was hard to prove constant true or false. This
     // provides an alternative mechanism to simplify these unreachable stores.
     string alloc_extent_name = op->name + ".total_extent_bytes";
-    if (bounds_and_alignment_info.contains(alloc_extent_name)) {
+    if (is_const_one(op->predicate) &&
+        bounds_and_alignment_info.contains(alloc_extent_name)) {
         if (index_info.max_defined && index_info.max < 0) {
             in_unreachable = true;
             return Evaluate::make(unreachable());

test/correctness/fuzz_schedule.cpp

@@ -54,6 +54,26 @@ int main(int argc, char **argv) {
         check_blur_output(buf, correct);
     }
 
+    // https://github.com/halide/Halide/issues/7873
+    {
+        Func input("input");
+        Func local_sum("local_sum");
+        Func blurry("blurry");
+        Var x("x"), y("y");
+        RVar yryf;
+        input(x, y) = 2 * x + 5 * y;
+        RDom r(-2, 5, -2, 5, "rdom_r");
+        local_sum(x, y) = 0;
+        local_sum(x, y) += input(x + r.x, y + r.y);
+        blurry(x, y) = cast<int32_t>(local_sum(x, y) / 25);
+        Var xo, xi;
+        local_sum.split(x, xo, xi, 4, TailStrategy::PredicateStores);
+        local_sum.update(0).unscheduled();
+        Pipeline p({blurry});
+        Buffer<int> buf = p.realize({32, 32});
+        check_blur_output(buf, correct);
+    }
+
     printf("Success!\n");
 
     return 0;