Commit 99422cb5284f3e15c1b5a8598a6b1622c0e7b6ca | zig

author	Luuk de Gram <luuk@degram.dev> 2023-05-08 20:22:55+02:00
committer	Luuk de Gram <luuk@degram.dev> 2023-05-19 20:19:00+02:00
log	99422cb5284f3e15c1b5a8598a6b1622c0e7b6ca
tree	cf712b929c5f3fd1128cd83a97863203c762d8f4
parent	f2860bb4f40565e43f51757e6cb604bb2df16ae0
signature	Commit is signed but in an unrecognized format.

wasm: add `dead` tag to `WValue`

This new tag is used for freed locals that are not allowed to have any
remaining references pointing to it. This new tag allows us to easily
identify liveness bugs. Previously we would set the entire region to
`undefined` which would incorrectly set the tag to `function_index`,
making codegen think it was a valid `WValue` while it wasn't.

1 files changed, 9 insertions(+), 2 deletions(-)

src
- arch
  - wasm
    CodeGen.zig

src/arch/wasm/CodeGen.zig+9-2

...	...	@@ -29,6 +29,9 @@ const errUnionErrorOffset = codegen.errUnionErrorOffset;
29	29
30	30	/// Wasm Value, created when generating an instruction
31	31	const WValue = union(enum) {
	32	/// `WValue` which has been freed and may no longer hold
	33	/// any references.
	34	dead: void,
32	35	/// May be referenced but is unused
33	36	none: void,
34	37	/// The value lives on top of the stack
...	...	@@ -86,6 +89,7 @@ const WValue = union(enum) {
86	89	fn offset(value: WValue) u32 {
87	90	switch (value) {
88	91	.stack_offset => \|stack_offset\| return stack_offset.value,
	92	.dead => unreachable,
89	93	else => return 0,
90	94	}
91	95	}
...	...	@@ -123,7 +127,7 @@ const WValue = union(enum) {
123	127	.f64 => gen.free_locals_f64.append(gen.gpa, local_value) catch return,
124	128	.v128 => gen.free_locals_v128.append(gen.gpa, local_value) catch return,
125	129	}
126		value.* = undefined;
	130	value.* = .dead;
127	131	}
128	132	};
129	133
...	...	@@ -832,6 +836,7 @@ const Branch = struct {
832	836
833	837	fn deinit(branch: *Branch, gpa: Allocator) void {
834	838	branch.values.deinit(gpa);
	839	branch.* = undefined;
835	840	}
836	841	};
837	842
...	...	@@ -884,7 +889,7 @@ fn processDeath(func: *CodeGen, ref: Air.Inst.Ref) void {
884	889	if (value.local.value < reserved_indexes) {
885	890	return; // function arguments can never be re-used
886	891	}
887		log.debug("Decreasing reference for ref: %{?d}, using local '{d}'\n", .{ Air.refToIndex(ref), value.local.value });
	892	log.debug("Decreasing reference for ref: %{?d}, using local '{d}'", .{ Air.refToIndex(ref), value.local.value });
888	893	value.local.references -= 1; // if this panics, a call to `reuseOperand` was forgotten by the developer
889	894	if (value.local.references == 0) {
890	895	value.free(func);
...	...	@@ -1030,6 +1035,7 @@ fn genBlockType(ty: Type, target: std.Target) u8 {
1030	1035	/// Writes the bytecode depending on the given `WValue` in `val`
1031	1036	fn emitWValue(func: *CodeGen, value: WValue) InnerError!void {
1032	1037	switch (value) {
	1038	.dead => unreachable, // reference to free'd `WValue` (missing reuseOperand?)
1033	1039	.none, .stack => {}, // no-op
1034	1040	.local => \|idx\| try func.addLabel(.local_get, idx.value),
1035	1041	.imm32 => \|val\| try func.addImm32(@bitCast(i32, val)),
...	...	@@ -1226,6 +1232,7 @@ fn genFunc(func: *CodeGen) InnerError!void {
1226	1232	defer {
1227	1233	var outer_branch = func.branches.pop();
1228	1234	outer_branch.deinit(func.gpa);
	1235	assert(func.branches.items.len == 0); // missing branch merge
1229	1236	}
1230	1237	// Generate MIR for function body
1231	1238	try func.genBody(func.air.getMainBody());