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Define the behaviour of integer division by zero

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This commit is contained in:
gingerBill
2025-08-08 10:00:11 +01:00
parent 3194fda8f3
commit e4a0228a80
4 changed files with 247 additions and 30 deletions
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188
src/llvm_backend_expr.cpp
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@@ -283,6 +283,12 @@ gb_internal lbValue lb_emit_unary_arith(lbProcedure *p, TokenKind op, lbValue x,
return res;
}
gb_internal IntegerDivisionByZeroKind lb_check_for_integer_division_by_zero(lbProcedure *p) {
// TODO(bill): per file `#+feature` flags
return build_context.integer_division_by_zero_behaviour;
}
gb_internal bool lb_try_direct_vector_arith(lbProcedure *p, TokenKind op, lbValue lhs, lbValue rhs, Type *type, lbValue *res_) {
GB_ASSERT(is_type_array_like(type));
Type *elem_type = base_array_type(type);
@@ -354,7 +360,6 @@ gb_internal bool lb_try_direct_vector_arith(lbProcedure *p, TokenKind op, lbValu
}
} else {
switch (op) {
case Token_Add:
z = LLVMBuildAdd(p->builder, x, y, "");
@@ -366,17 +371,15 @@ gb_internal bool lb_try_direct_vector_arith(lbProcedure *p, TokenKind op, lbValu
z = LLVMBuildMul(p->builder, x, y, "");
break;
case Token_Quo:
if (is_type_unsigned(integral_type)) {
z = LLVMBuildUDiv(p->builder, x, y, "");
} else {
z = LLVMBuildSDiv(p->builder, x, y, "");
{
auto *call = is_type_unsigned(integral_type) ? LLVMBuildUDiv : LLVMBuildSDiv;
z = call(p->builder, x, y, "");
}
break;
case Token_Mod:
if (is_type_unsigned(integral_type)) {
z = LLVMBuildURem(p->builder, x, y, "");
} else {
z = LLVMBuildSRem(p->builder, x, y, "");
{
auto *call = is_type_unsigned(integral_type) ? LLVMBuildURem : LLVMBuildSRem;
z = call(p->builder, x, y, "");
}
break;
case Token_ModMod:
@@ -1111,6 +1114,150 @@ gb_internal lbValue lb_emit_arith_matrix(lbProcedure *p, TokenKind op, lbValue l
return {};
}
gb_internal LLVMValueRef lb_integer_division(lbProcedure *p, LLVMValueRef lhs, LLVMValueRef rhs, bool is_signed) {
LLVMTypeRef type = LLVMTypeOf(rhs);
GB_ASSERT(LLVMTypeOf(lhs) == type);
auto *call = is_signed ? LLVMBuildSDiv : LLVMBuildUDiv;
LLVMValueRef incoming_values[2] = {};
LLVMBasicBlockRef incoming_blocks[2] = {};
lbBlock *safe_block = lb_create_block(p, "div.safe");
lbBlock *edge_case_block = lb_create_block(p, "div.edge");
lbBlock *done_block = lb_create_block(p, "div.done");
LLVMValueRef zero = LLVMConstNull(type);
LLVMValueRef dem_check = LLVMBuildICmp(p->builder, LLVMIntNE, rhs, zero, "");
lbValue cond = {dem_check, t_untyped_bool};
lb_emit_if(p, cond, safe_block, edge_case_block);
lb_start_block(p, safe_block);
incoming_values[0] = call(p->builder, lhs, rhs, "");
lb_emit_jump(p, done_block);
lb_start_block(p, edge_case_block);
incoming_values[1] = zero;
switch (lb_check_for_integer_division_by_zero(p)) {
case IntegerDivisionByZero_Trap:
lb_call_intrinsic(p, "llvm.trap", nullptr, 0, nullptr, 0);
LLVMBuildUnreachable(p->builder);
break;
case IntegerDivisionByZero_Zero:
// Already fine
break;
}
lb_emit_jump(p, done_block);
lb_start_block(p, done_block);
LLVMValueRef res = incoming_values[0];
switch (lb_check_for_integer_division_by_zero(p)) {
case IntegerDivisionByZero_Trap:
res = incoming_values[0];
break;
case IntegerDivisionByZero_Zero:
res = LLVMBuildPhi(p->builder, type, "");
GB_ASSERT(p->curr_block->preds.count >= 2);
incoming_blocks[0] = p->curr_block->preds[0]->block;
incoming_blocks[1] = p->curr_block->preds[1]->block;
LLVMAddIncoming(res, incoming_values, incoming_blocks, 2);
break;
}
return res;
}
gb_internal LLVMValueRef lb_integer_modulo(lbProcedure *p, LLVMValueRef lhs, LLVMValueRef rhs, bool is_unsigned, bool is_floored) {
LLVMTypeRef type = LLVMTypeOf(rhs);
GB_ASSERT(LLVMTypeOf(lhs) == type);
LLVMValueRef incoming_values[2] = {};
LLVMBasicBlockRef incoming_blocks[2] = {};
lbBlock *safe_block = lb_create_block(p, "div.safe");
lbBlock *edge_case_block = lb_create_block(p, "div.edge");
lbBlock *done_block = lb_create_block(p, "div.done");
LLVMValueRef zero = LLVMConstNull(type);
LLVMValueRef dem_check = LLVMBuildICmp(p->builder, LLVMIntNE, rhs, zero, "");
lbValue cond = {dem_check, t_untyped_bool};
lb_emit_if(p, cond, safe_block, edge_case_block);
lb_start_block(p, safe_block);
if (is_floored) { // %%
if (is_unsigned) {
incoming_values[0] = LLVMBuildURem(p->builder, lhs, rhs, "");
} else {
LLVMValueRef a = LLVMBuildSRem(p->builder, lhs, rhs, "");
LLVMValueRef b = LLVMBuildAdd(p->builder, a, rhs, "");
LLVMValueRef c = LLVMBuildSRem(p->builder, b, rhs, "");
incoming_values[0] = c;
}
} else { // %
if (is_unsigned) {
incoming_values[0] = LLVMBuildURem(p->builder, lhs, rhs, "");
} else {
incoming_values[0] = LLVMBuildSRem(p->builder, lhs, rhs, "");
}
}
lb_emit_jump(p, done_block);
lb_start_block(p, edge_case_block);
/*
NOTE(bill): @integer division by zero rules
truncated: r = a - b*trunc(a/b)
floored: r = a - b*floor(a/b)
IFF a/0 == 0, then (a%0 == a) or (a%%0 == a)
*/
incoming_values[1] = lhs;
switch (lb_check_for_integer_division_by_zero(p)) {
case IntegerDivisionByZero_Trap:
lb_call_intrinsic(p, "llvm.trap", nullptr, 0, nullptr, 0);
LLVMBuildUnreachable(p->builder);
break;
case IntegerDivisionByZero_Zero:
// Already fine
break;
}
lb_emit_jump(p, done_block);
lb_start_block(p, done_block);
LLVMValueRef res = incoming_values[0];
switch (lb_check_for_integer_division_by_zero(p)) {
case IntegerDivisionByZero_Trap:
res = incoming_values[0];
break;
case IntegerDivisionByZero_Zero:
res = LLVMBuildPhi(p->builder, type, "");
GB_ASSERT(p->curr_block->preds.count >= 2);
incoming_blocks[0] = p->curr_block->preds[0]->block;
incoming_blocks[1] = p->curr_block->preds[1]->block;
LLVMAddIncoming(res, incoming_values, incoming_blocks, 2);
break;
}
return res;
}
gb_internal lbValue lb_emit_arith(lbProcedure *p, TokenKind op, lbValue lhs, lbValue rhs, Type *type) {
@@ -1350,33 +1497,20 @@ handle_op:;
if (is_type_float(integral_type)) {
res.value = LLVMBuildFDiv(p->builder, lhs.value, rhs.value, "");
return res;
} else if (is_type_unsigned(integral_type)) {
res.value = LLVMBuildUDiv(p->builder, lhs.value, rhs.value, "");
} else {
res.value = lb_integer_division(p, lhs.value, rhs.value, !is_type_unsigned(integral_type));
return res;
}
res.value = LLVMBuildSDiv(p->builder, lhs.value, rhs.value, "");
return res;
case Token_Mod:
if (is_type_float(integral_type)) {
res.value = LLVMBuildFRem(p->builder, lhs.value, rhs.value, "");
return res;
} else if (is_type_unsigned(integral_type)) {
res.value = LLVMBuildURem(p->builder, lhs.value, rhs.value, "");
return res;
}
res.value = LLVMBuildSRem(p->builder, lhs.value, rhs.value, "");
res.value = lb_integer_modulo(p, lhs.value, rhs.value, is_type_unsigned(integral_type), /*is_floored*/false);
return res;
case Token_ModMod:
if (is_type_unsigned(integral_type)) {
res.value = LLVMBuildURem(p->builder, lhs.value, rhs.value, "");
return res;
} else {
LLVMValueRef a = LLVMBuildSRem(p->builder, lhs.value, rhs.value, "");
LLVMValueRef b = LLVMBuildAdd(p->builder, a, rhs.value, "");
LLVMValueRef c = LLVMBuildSRem(p->builder, b, rhs.value, "");
res.value = c;
return res;
}
res.value = lb_integer_modulo(p, lhs.value, rhs.value, is_type_unsigned(integral_type), /*is_floored*/true);
return res;
case Token_And:
res.value = LLVMBuildAnd(p->builder, lhs.value, rhs.value, "");