sema: fix safe integer arithmetic operations on undefined values

Previously `@as(i64, undefined) +% 1` would produce `@as(@TypeOf(undefined), undefined)` which now gives `@as(i64, undefined)`.
Previously `@as(i64, undefined) +| 1` would hit an assertion which now gives `@as(i64, undefined)`.

9 files changed, 249 insertions, 9 deletions

diff --git a/test/cases/compile_errors/add_on_undefined_value.zig b/test/cases/compile_errors/add_on_undefined_value.zig
index b59de233c5..eb081a8510 100644
--- a/test/cases/compile_errors/add_on_undefined_value.zig
+++ b/test/cases/compile_errors/add_on_undefined_value.zig
@@ -1,10 +1,24 @@
 comptime {
-    const a: i64 = undefined;
-    _ = a + a;
+    const undef: i64 = undefined;
+    const not_undef: i64 = 32;
+
+    // If either of the operands are zero, then the other operand is returned.
+    @compileLog(undef + 0);
+    @compileLog(not_undef + 0);
+    @compileLog(0 + undef);
+    @compileLog(0 + not_undef);
+
+    _ = undef + undef;
 }
 
 // error
 // backend=stage2
 // target=native
 //
-// :3:13: error: use of undefined value here causes undefined behavior
+// :11:17: error: use of undefined value here causes undefined behavior
+//
+// Compile Log Output:
+// @as(i64, undefined)
+// @as(i64, 32)
+// @as(i64, undefined)
+// @as(i64, 32)
diff --git a/test/cases/compile_errors/add_sat_on_undefined_value.zig b/test/cases/compile_errors/add_sat_on_undefined_value.zig
new file mode 100644
index 0000000000..e23a985d1a
--- /dev/null
+++ b/test/cases/compile_errors/add_sat_on_undefined_value.zig
@@ -0,0 +1,31 @@
+comptime {
+    const undef: i64 = undefined;
+    const not_undef: i64 = 32;
+
+    // If either of the operands are zero, then the other operand is returned.
+    @compileLog(undef +| 0);
+    @compileLog(not_undef +| 0);
+    @compileLog(0 +| undef);
+    @compileLog(0 +| not_undef);
+    // If either of the operands are undefined, the result is undefined.
+    @compileLog(undef +| 1);
+    @compileLog(not_undef +| 1);
+    @compileLog(1 +| undef);
+    @compileLog(1 +| not_undef);
+}
+
+// error
+// backend=stage2
+// target=native
+//
+// :6:5: error: found compile log statement
+//
+// Compile Log Output:
+// @as(i64, undefined)
+// @as(i64, 32)
+// @as(i64, undefined)
+// @as(i64, 32)
+// @as(i64, undefined)
+// @as(i64, 33)
+// @as(i64, undefined)
+// @as(i64, 33)
diff --git a/test/cases/compile_errors/add_wrap_on_undefined_value.zig b/test/cases/compile_errors/add_wrap_on_undefined_value.zig
new file mode 100644
index 0000000000..b957485735
--- /dev/null
+++ b/test/cases/compile_errors/add_wrap_on_undefined_value.zig
@@ -0,0 +1,31 @@
+comptime {
+    const undef: i64 = undefined;
+    const not_undef: i64 = 32;
+
+    // If either of the operands are zero, then the other operand is returned.
+    @compileLog(undef +% 0);
+    @compileLog(not_undef +% 0);
+    @compileLog(0 +% undef);
+    @compileLog(0 +% not_undef);
+    // If either of the operands are undefined, the result is undefined.
+    @compileLog(undef +% 1);
+    @compileLog(not_undef +% 1);
+    @compileLog(1 +% undef);
+    @compileLog(1 +% not_undef);
+}
+
+// error
+// backend=stage2
+// target=native
+//
+// :6:5: error: found compile log statement
+//
+// Compile Log Output:
+// @as(i64, undefined)
+// @as(i64, 32)
+// @as(i64, undefined)
+// @as(i64, 32)
+// @as(i64, undefined)
+// @as(i64, 33)
+// @as(i64, undefined)
+// @as(i64, 33)
diff --git a/test/cases/compile_errors/mult_on_undefined_value.zig b/test/cases/compile_errors/mult_on_undefined_value.zig
index 1e65797153..3516253d5c 100644
--- a/test/cases/compile_errors/mult_on_undefined_value.zig
+++ b/test/cases/compile_errors/mult_on_undefined_value.zig
@@ -1,10 +1,38 @@
 comptime {
-    const a: i64 = undefined;
-    _ = a * a;
+    const undef: i64 = undefined;
+    const not_undef: i64 = 32;
+
+    // If either of the operands are zero, the result is zero.
+    @compileLog(undef * 0);
+    @compileLog(not_undef * 0);
+    @compileLog(0 * undef);
+    @compileLog(0 * not_undef);
+
+    // If either of the operands are one, the result is the other
+    // operand, even if it is undefined.
+    @compileLog(undef * 1);
+    @compileLog(not_undef * 1);
+    @compileLog(1 * undef);
+    @compileLog(1 * not_undef);
+
+    // If either of the operands are undefined, it's a compile error
+    // because there is a possible value for which the addition would
+    // overflow (max_int), causing illegal behavior.
+    _ = undef * undef;
 }
 
 // error
 // backend=stage2
 // target=native
 //
-// :3:13: error: use of undefined value here causes undefined behavior
+// :21:17: error: use of undefined value here causes undefined behavior
+//
+// Compile Log Output:
+// @as(i64, 0)
+// @as(i64, 0)
+// @as(i64, 0)
+// @as(i64, 0)
+// @as(i64, undefined)
+// @as(i64, 32)
+// @as(i64, undefined)
+// @as(i64, 32)
diff --git a/test/cases/compile_errors/mult_sat_on_undefined_value.zig b/test/cases/compile_errors/mult_sat_on_undefined_value.zig
new file mode 100644
index 0000000000..987161c8ed
--- /dev/null
+++ b/test/cases/compile_errors/mult_sat_on_undefined_value.zig
@@ -0,0 +1,38 @@
+comptime {
+    const undef: i64 = undefined;
+    const not_undef: i64 = 32;
+
+    // If either of the operands are zero, the result is zero.
+    @compileLog(undef *| 0);
+    @compileLog(not_undef *| 0);
+    @compileLog(0 *| undef);
+    @compileLog(0 *| not_undef);
+
+    // If either of the operands are one, result is the other operand.
+    @compileLog(undef *| 1);
+    @compileLog(not_undef *| 1);
+    @compileLog(1 *| undef);
+    @compileLog(1 *| not_undef);
+
+    // If either of the operands are undefined, result is undefined.
+    @compileLog(undef *| 2);
+    @compileLog(2 *| undef);
+}
+
+// error
+// backend=stage2
+// target=native
+//
+// :6:5: error: found compile log statement
+//
+// Compile Log Output:
+// @as(i64, 0)
+// @as(i64, 0)
+// @as(i64, 0)
+// @as(i64, 0)
+// @as(i64, undefined)
+// @as(i64, 32)
+// @as(i64, undefined)
+// @as(i64, 32)
+// @as(i64, undefined)
+// @as(i64, undefined)
diff --git a/test/cases/compile_errors/mult_wrap_on_undefined_value.zig b/test/cases/compile_errors/mult_wrap_on_undefined_value.zig
new file mode 100644
index 0000000000..2ecb6753f6
--- /dev/null
+++ b/test/cases/compile_errors/mult_wrap_on_undefined_value.zig
@@ -0,0 +1,38 @@
+comptime {
+    const undef: i64 = undefined;
+    const not_undef: i64 = 32;
+
+    // If either of the operands are zero, the result is zero.
+    @compileLog(undef *% 0);
+    @compileLog(not_undef *% 0);
+    @compileLog(0 *% undef);
+    @compileLog(0 *% not_undef);
+
+    // If either of the operands are one, result is the other operand.
+    @compileLog(undef *% 1);
+    @compileLog(not_undef *% 1);
+    @compileLog(1 *% undef);
+    @compileLog(1 *% not_undef);
+
+    // If either of the operands are undefined, result is undefined.
+    @compileLog(undef *% 2);
+    @compileLog(2 *% undef);
+}
+
+// error
+// backend=stage2
+// target=native
+//
+// :6:5: error: found compile log statement
+//
+// Compile Log Output:
+// @as(i64, 0)
+// @as(i64, 0)
+// @as(i64, 0)
+// @as(i64, 0)
+// @as(i64, undefined)
+// @as(i64, 32)
+// @as(i64, undefined)
+// @as(i64, 32)
+// @as(i64, undefined)
+// @as(i64, undefined)
diff --git a/test/cases/compile_errors/sub_on_undefined_value.zig b/test/cases/compile_errors/sub_on_undefined_value.zig
index de305be576..5d2510f263 100644
--- a/test/cases/compile_errors/sub_on_undefined_value.zig
+++ b/test/cases/compile_errors/sub_on_undefined_value.zig
@@ -1,10 +1,20 @@
 comptime {
-    const a: i64 = undefined;
-    _ = a - a;
+    const undef: i64 = undefined;
+    const not_undef: i64 = 32;
+
+    // If the rhs is zero, then the other operand is returned, even if it is undefined.
+    @compileLog(undef - 0);
+    @compileLog(not_undef - 0);
+
+    _ = undef - undef;
 }
 
 // error
 // backend=stage2
 // target=native
 //
-// :3:13: error: use of undefined value here causes undefined behavior
+// :9:17: error: use of undefined value here causes undefined behavior
+//
+// Compile Log Output:
+// @as(i64, undefined)
+// @as(i64, 32)
diff --git a/test/cases/compile_errors/sub_sat_on_undefined_value.zig b/test/cases/compile_errors/sub_sat_on_undefined_value.zig
new file mode 100644
index 0000000000..967f24130e
--- /dev/null
+++ b/test/cases/compile_errors/sub_sat_on_undefined_value.zig
@@ -0,0 +1,25 @@
+comptime {
+    const undef: i64 = undefined;
+    const not_undef: i64 = 32;
+
+    // If the RHS is zero, then the LHS is returned, even if it is undefined.
+    @compileLog(undef -| 0);
+    @compileLog(not_undef -| 0);
+    // If either of the operands are undefined, the result is undefined.
+    @compileLog(undef -| not_undef);
+    @compileLog(not_undef -| undef);
+    @compileLog(undef -| undef);
+}
+
+// error
+// backend=stage2
+// target=native
+//
+// :6:5: error: found compile log statement
+//
+// Compile Log Output:
+// @as(i64, undefined)
+// @as(i64, 32)
+// @as(i64, undefined)
+// @as(i64, undefined)
+// @as(i64, undefined)
diff --git a/test/cases/compile_errors/sub_wrap_on_undefined_value.zig b/test/cases/compile_errors/sub_wrap_on_undefined_value.zig
new file mode 100644
index 0000000000..12dfeff4e5
--- /dev/null
+++ b/test/cases/compile_errors/sub_wrap_on_undefined_value.zig
@@ -0,0 +1,25 @@
+comptime {
+    const undef: i64 = undefined;
+    const not_undef: i64 = 32;
+
+    // If the RHS is zero, then the LHS is returned, even if it is undefined.
+    @compileLog(undef -% 0);
+    @compileLog(not_undef -% 0);
+    // If either of the operands are undefined, the result is undefined.
+    @compileLog(undef -% not_undef);
+    @compileLog(not_undef -% undef);
+    @compileLog(undef -% undef);
+}
+
+// error
+// backend=stage2
+// target=native
+//
+// :6:5: error: found compile log statement
+//
+// Compile Log Output:
+// @as(i64, undefined)
+// @as(i64, 32)
+// @as(i64, undefined)
+// @as(i64, undefined)
+// @as(i64, undefined)