From 2a4e06bcb30f71e83b14026bcbade6aac3aece84 Mon Sep 17 00:00:00 2001 From: mlugg Date: Mon, 10 Mar 2025 03:31:36 +0000 Subject: Sema: rewrite comptime arithmetic This commit reworks how Sema handles arithmetic on comptime-known values, fixing many bugs in the process. The general pattern is that arithmetic on comptime-known values is now handled by the new namespace `Sema.arith`. Functions handling comptime arithmetic no longer live on `Value`; this is because some of them can emit compile errors, so some *can't* go on `Value`. Only semantic analysis should really be doing arithmetic on `Value`s anyway, so it makes sense for it to integrate more tightly with `Sema`. This commit also implements more coherent rules surrounding how `undefined` interacts with comptime and mixed-comptime-runtime arithmetic. The rules are as follows. * If an operation cannot trigger Illegal Behavior, and any operand is `undefined`, the result is `undefined`. This includes operations like `0 *| undef`, where the LHS logically *could* be used to determine a defined result. This is partly to simplify the language, but mostly to permit codegen backends to represent `undefined` values as completely invalid states. * If an operation *can* trigger Illegal Behvaior, and any operand is `undefined`, then Illegal Behavior results. This occurs even if the operand in question isn't the one that "decides" illegal behavior; for instance, `undef / 1` is undefined. This is for the same reasons as described above. * An operation which would trigger Illegal Behavior, when evaluated at comptime, instead triggers a compile error. Additionally, if one operand is comptime-known undef, such that the other (runtime-known) operand isn't needed to determine that Illegal Behavior would occur, the compile error is triggered. * The only situation in which an operation with one comptime-known operand has a comptime-known result is if that operand is undefined, in which case the result is either undefined or a compile error per the above rules. This could potentially be loosened in future (for instance, `0 * rt` could be comptime-known 0 with a runtime assertion that `rt` is not undefined), but at least for now, defining it more conservatively simplifies the language and allows us to easily change this in future if desired. This commit fixes many bugs regarding the handling of `undefined`, particularly in vectors. Along with a collection of smaller tests, two very large test cases are added to check arithmetic on `undefined`. The operations which have been rewritten in this PR are: * `+`, `+%`, `+|`, `@addWithOverflow` * `-`, `-%`, `-|`, `@subWithOverflow` * `*`, `*%`, `*|`, `@mulWithOverflow` * `/`, `@divFloor`, `@divTrunc`, `@divExact` * `%`, `@rem`, `@mod` Other arithmetic operations are currently unchanged. Resolves: #22743 Resolves: #22745 Resolves: #22748 Resolves: #22749 Resolves: #22914 --- .../compile_errors/mult_on_undefined_value.zig | 38 ---------------------- 1 file changed, 38 deletions(-) delete mode 100644 test/cases/compile_errors/mult_on_undefined_value.zig (limited to 'test/cases/compile_errors/mult_on_undefined_value.zig') diff --git a/test/cases/compile_errors/mult_on_undefined_value.zig b/test/cases/compile_errors/mult_on_undefined_value.zig deleted file mode 100644 index 3516253d5c..0000000000 --- a/test/cases/compile_errors/mult_on_undefined_value.zig +++ /dev/null @@ -1,38 +0,0 @@ -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, 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 -// -// :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) -- cgit v1.2.3