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Fix calculation of new alignment factor

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This commit is contained in:
LemonBoy 2020-01-08 21:02:05 +01:00
parent 7fe13f4a86
commit 7ea7842ed0
2 changed files with 28 additions and 14 deletions
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11
src/ir.cpp
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@ -15801,8 +15801,15 @@ static IrInstruction *ir_analyze_bin_op_math(IrAnalyze *ira, IrInstructionBinOp
if ((err = resolve_ptr_align(ira, op1->value->type, &align_bytes)))
return ira->codegen->invalid_instruction;
if (byte_offset != 0 && byte_offset % align_bytes != 0)
result_type = adjust_ptr_align(ira->codegen, result_type, 1);
if (byte_offset & (align_bytes - 1)) {
// The resulting pointer is aligned to the lcd between the
// offset (an arbitrary number) and the alignment factor (always
// a power of two, non zero)
uint32_t new_align = 1 << ctzll(byte_offset | align_bytes);
// Rough guard to prevent overflows
assert(new_align);
result_type = adjust_ptr_align(ira->codegen, result_type, new_align);
}
} else {
// The addend is not a comptime-known value
result_type = adjust_ptr_align(ira->codegen, result_type, 1);

31
test/stage1/behavior/pointers.zig
View File

@ -290,17 +290,24 @@ test "pointer to array at fixed address" {
}
test "pointer arithmetic affects the alignment" {
var arr: [10]u8 align(2) = undefined;
var x: usize = 1;
{
var ptr: [*]align(8) u32 = undefined;
var x: usize = 1;
const ptr = @as([*]u8, &arr);
expect(@typeInfo(@TypeOf(ptr)).Pointer.alignment == 2);
const ptr1 = ptr + 1;
expect(@typeInfo(@TypeOf(ptr1)).Pointer.alignment == 1);
const ptr2 = ptr + 4;
expect(@typeInfo(@TypeOf(ptr2)).Pointer.alignment == 2);
const ptr3 = ptr + 0;
expect(@typeInfo(@TypeOf(ptr3)).Pointer.alignment == 2);
const ptr4 = ptr + x;
expect(@typeInfo(@TypeOf(ptr4)).Pointer.alignment == 1);
expect(@typeInfo(@TypeOf(ptr)).Pointer.alignment == 8);
const ptr1 = ptr + 1; // 1 * 4 = 4 -> lcd(4,8) = 4
expect(@typeInfo(@TypeOf(ptr1)).Pointer.alignment == 4);
const ptr2 = ptr + 4; // 4 * 4 = 16 -> lcd(16,8) = 8
expect(@typeInfo(@TypeOf(ptr2)).Pointer.alignment == 8);
const ptr3 = ptr + 0; // no-op
expect(@typeInfo(@TypeOf(ptr3)).Pointer.alignment == 8);
const ptr4 = ptr + x; // runtime-known addend
expect(@typeInfo(@TypeOf(ptr4)).Pointer.alignment == 1);
}
{
var ptr: [*]align(8) [3]u8 = undefined;
const ptr1 = ptr + 17; // 3 * 17 = 51
expect(@typeInfo(@TypeOf(ptr1)).Pointer.alignment == 1);
}
}