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translate-c: Support compound assignment of pointer and signed int

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This handles `ptr += idx` and `ptr -= idx` when `idx` is a
signed integer expression.
This commit is contained in:
Evan Haas 2021-03-05 09:54:59 -08:00 committed by Veikka Tuominen
parent 874c63f89c
commit 6d69a29d75
2 changed files with 35 additions and 9 deletions
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34
src/translate_c.zig
View File

@ -1111,6 +1111,22 @@ fn transOffsetOfExpr(
return fail(c, error.UnsupportedTranslation, expr.getBeginLoc(), "TODO: implement complex OffsetOfExpr translation", .{});
}
/// Cast a signed integer node to a usize, for use in pointer arithmetic. Negative numbers
/// will become very large positive numbers but that is ok since we only use this in
/// pointer arithmetic expressions, where wraparound will ensure we get the correct value.
/// node -> @bitCast(usize, @intCast(isize, node))
fn usizeCastForWrappingPtrArithmetic(gpa: *mem.Allocator, node: Node) TransError!Node {
const intcast_node = try Tag.int_cast.create(gpa, .{
.lhs = try Tag.identifier.create(gpa, "isize"),
.rhs = node,
});
return Tag.bit_cast.create(gpa, .{
.lhs = try Tag.identifier.create(gpa, "usize"),
.rhs = intcast_node,
});
}
/// Translate an arithmetic expression with a pointer operand and a signed-integer operand.
/// Zig requires a usize argument for pointer arithmetic, so we intCast to isize and then
/// bitcast to usize; pointer wraparound make the math work.
@ -1133,15 +1149,7 @@ fn transCreatePointerArithmeticSignedOp(
const lhs_node = try transExpr(c, scope, swizzled_lhs, .used);
const rhs_node = try transExpr(c, scope, swizzled_rhs, .used);
const intcast_node = try Tag.int_cast.create(c.arena, .{
.lhs = try Tag.identifier.create(c.arena, "isize"),
.rhs = rhs_node,
});
const bitcast_node = try Tag.bit_cast.create(c.arena, .{
.lhs = try Tag.identifier.create(c.arena, "usize"),
.rhs = intcast_node,
});
const bitcast_node = try usizeCastForWrappingPtrArithmetic(c.arena, rhs_node);
const arith_args = .{ .lhs = lhs_node, .rhs = bitcast_node };
const arith_node = try if (is_add) Tag.add.create(c.arena, arith_args) else Tag.sub.create(c.arena, arith_args);
@ -3035,6 +3043,7 @@ fn transCreateCompoundAssign(
const lhs_qt = getExprQualType(c, lhs);
const rhs_qt = getExprQualType(c, rhs);
const is_signed = cIsSignedInteger(lhs_qt);
const is_ptr_op_signed = qualTypeIsPtr(lhs_qt) and cIsSignedInteger(rhs_qt);
const requires_int_cast = blk: {
const are_integers = cIsInteger(lhs_qt) and cIsInteger(rhs_qt);
const are_same_sign = cIsSignedInteger(lhs_qt) == cIsSignedInteger(rhs_qt);
@ -3061,6 +3070,10 @@ fn transCreateCompoundAssign(
else
try transExpr(c, scope, rhs, .used);
if (is_ptr_op_signed) {
rhs_node = try usizeCastForWrappingPtrArithmetic(c.arena, rhs_node);
}
if (is_shift or requires_int_cast) {
// @intCast(rhs)
const cast_to_type = if (is_shift)
@ -3113,6 +3126,9 @@ fn transCreateCompoundAssign(
rhs_node = try Tag.int_cast.create(c.arena, .{ .lhs = cast_to_type, .rhs = rhs_node });
}
if (is_ptr_op_signed) {
rhs_node = try usizeCastForWrappingPtrArithmetic(c.arena, rhs_node);
}
const assign = try transCreateNodeInfixOp(c, &block_scope.base, op, ref_node, rhs_node, .used);
try block_scope.statements.append(assign);

10
test/run_translated_c.zig
View File

@ -1154,6 +1154,16 @@ pub fn addCases(cases: *tests.RunTranslatedCContext) void {
\\ y = x - idx;
\\ if (y != x + 1 || y != &array[6]) abort();
\\
\\ idx = 1;
\\ x += idx;
\\ if (x != &array[6]) abort();
\\ x -= idx;
\\ if (x != &array[5]) abort();
\\ y = (x += idx);
\\ if (y != x || y != &array[6]) abort();
\\ y = (x -= idx);
\\ if (y != x || y != &array[5]) abort();
\\
\\ return 0;
\\}
, "");