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Correct alignment calculation for runtime addends

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This commit is contained in:
LemonBoy 2020-01-09 11:56:45 +01:00
parent 7ea7842ed0
commit c51b79c56e
2 changed files with 25 additions and 18 deletions
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34
src/ir.cpp
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@ -15776,6 +15776,10 @@ static IrInstruction *ir_analyze_bin_op_math(IrAnalyze *ira, IrInstructionBinOp
return ir_const_undef(ira, &instruction->base, op1->value->type);
}
ZigType *elem_type = op1->value->type->data.pointer.child_type;
if ((err = type_resolve(ira->codegen, elem_type, ResolveStatusSizeKnown)))
return ira->codegen->invalid_instruction;
// NOTE: this variable is meaningful iff op2_val is not null!
uint64_t byte_offset;
if (op2_val != nullptr) {
@ -15783,9 +15787,6 @@ static IrInstruction *ir_analyze_bin_op_math(IrAnalyze *ira, IrInstructionBinOp
if (!ir_resolve_usize(ira, casted_op2, &elem_offset))
return ira->codegen->invalid_instruction;
ZigType *elem_type = op1->value->type->data.pointer.child_type;
if ((err = type_resolve(ira->codegen, elem_type, ResolveStatusSizeKnown)))
return ira->codegen->invalid_instruction;
byte_offset = type_size(ira->codegen, elem_type) * elem_offset;
}
@ -15795,24 +15796,23 @@ static IrInstruction *ir_analyze_bin_op_math(IrAnalyze *ira, IrInstructionBinOp
}
ZigType *result_type = op1->value->type;
// The resulting pointer may not be aligned anymore
if (op2_val != nullptr) {
// Calculate the new alignment of the pointer
{
uint32_t align_bytes;
if ((err = resolve_ptr_align(ira, op1->value->type, &align_bytes)))
return ira->codegen->invalid_instruction;
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);
// If the addend is not a comptime-known value we can still count on
// it being a multiple of the type size
uint32_t addend = op2_val ? byte_offset : type_size(ira->codegen, elem_type);
// 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(addend | align_bytes);
// Rough guard to prevent overflows
assert(new_align);
result_type = adjust_ptr_align(ira->codegen, result_type, new_align);
}
if (op2_val != nullptr && op1_val != nullptr &&

9
test/stage1/behavior/pointers.zig
View File

@ -302,12 +302,19 @@ test "pointer arithmetic affects the alignment" {
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);
expect(@typeInfo(@TypeOf(ptr4)).Pointer.alignment == 4);
}
{
var ptr: [*]align(8) [3]u8 = undefined;
var x: usize = 1;
const ptr1 = ptr + 17; // 3 * 17 = 51
expect(@typeInfo(@TypeOf(ptr1)).Pointer.alignment == 1);
const ptr2 = ptr + x; // runtime-known addend
expect(@typeInfo(@TypeOf(ptr2)).Pointer.alignment == 1);
const ptr3 = ptr + 8; // 3 * 8 = 24 -> lcd(8,24) = 8
expect(@typeInfo(@TypeOf(ptr3)).Pointer.alignment == 8);
const ptr4 = ptr + 4; // 3 * 4 = 12 -> lcd(8,12) = 4
expect(@typeInfo(@TypeOf(ptr4)).Pointer.alignment == 4);
}
}