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[CC] [autodiff] Support AdStack on C backend #1752

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merged 6 commits into from
Aug 29, 2020
Merged

[CC] [autodiff] Support AdStack on C backend #1752

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257cfb2
tmp
archibate Aug 23, 2020
3ebf2ca
fix the stupid init issue
archibate Aug 23, 2020
6a83777
[skip ci] enforce code format
taichi-gardener Aug 23, 2020
4143a3e
[skip ci] Update taichi/backends/cc/runtime/base.h
archibate Aug 28, 2020
cadd0aa
Merge branch 'master' into cc-adstack
archibate Aug 28, 2020
bdc1559
Merge branch 'master' into cc-adstack
archibate Aug 28, 2020
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60 changes: 59 additions & 1 deletion taichi/backends/cc/codegen_cc.cpp
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Expand Up @@ -48,7 +48,7 @@ class CCTransformer : public IRVisitor {
config.demote_dense_struct_fors = true;
irpass::compile_to_executable(ir, config,
/*vectorize=*/false, kernel->grad,
/*ad_use_stack=*/false, config.print_ir,
/*ad_use_stack=*/true, config.print_ir,
/*lower_global_access*/ true);
}

Expand Down Expand Up @@ -520,6 +520,64 @@ class CCTransformer : public IRVisitor {
data_type_short_name(stmt->ret_type.data_type));
}

void visit(StackAllocaStmt *stmt) override {
TI_ASSERT(stmt->width() == 1);

const auto &var_name = stmt->raw_name();
emit("Ti_u8 {}[{}];", var_name, stmt->size_in_bytes() + sizeof(uint32_t));
emit("Ti_ad_stack_init({});", var_name);
}

void visit(StackPopStmt *stmt) override {
emit("Ti_ad_stack_pop({});", stmt->stack->raw_name());
}

void visit(StackPushStmt *stmt) override {
auto *stack = stmt->stack->as<StackAllocaStmt>();
const auto &stack_name = stack->raw_name();
auto elem_size = stack->element_size_in_bytes();
emit("Ti_ad_stack_push({}, {});", stack_name, elem_size);
auto primal_name = stmt->raw_name() + "_primal_";
auto dt_name = cc_data_type_name(stmt->element_type());
auto var = define_var(dt_name + " *", primal_name);
emit("{} = ({} *) Ti_ad_stack_top_primal({}, {});", var, dt_name,
stack_name, elem_size);
emit("*{} = {};", primal_name, stmt->v->raw_name());
}

void visit(StackLoadTopStmt *stmt) override {
auto *stack = stmt->stack->as<StackAllocaStmt>();
const auto primal_name = stmt->raw_name() + "_primal_";
auto dt_name = cc_data_type_name(stmt->element_type());
auto var = define_var(dt_name + " *", primal_name);
emit("{} = ({} *)Ti_ad_stack_top_primal({}, {});", var, dt_name,
stack->raw_name(), stack->element_size_in_bytes());
emit("{} = *{};", define_var(dt_name, stmt->raw_name()), primal_name);
}

void visit(StackLoadTopAdjStmt *stmt) override {
auto *stack = stmt->stack->as<StackAllocaStmt>();
const auto adjoint_name = stmt->raw_name() + "_adjoint_";
auto dt_name = cc_data_type_name(stmt->element_type());
auto var = define_var(dt_name + " *", adjoint_name);
emit("{} = ({} *)Ti_ad_stack_top_adjoint({}, {});", var, dt_name,
stack->raw_name(), stack->element_size_in_bytes());
emit("{} = *{};", define_var(dt_name, stmt->raw_name()), adjoint_name);
}

void visit(StackAccAdjointStmt *stmt) override {
auto *stack = stmt->stack->as<StackAllocaStmt>();
const auto adjoint_name = stmt->raw_name() + "_adjoint_";
auto dt_name = cc_data_type_name(stmt->element_type());
auto var = define_var(dt_name + " *", adjoint_name);
emit("{} = ({} *)Ti_ad_stack_top_adjoint({}, {});", var, dt_name,
stack->raw_name(), stack->element_size_in_bytes());
emit("printf(\"%d\\n\", *Ti_ad_stack_n({}));", stack->raw_name());
emit("printf(\"%p\\n\", {});", stack->raw_name());
emit("printf(\"%p\\n\", {});", adjoint_name);
emit("*{} += {};", adjoint_name, stmt->v->raw_name());
}

template <typename... Args>
void emit(std::string f, Args &&... args) {
line_appender.append(std::move(f), std::move(args)...);
Expand Down
44 changes: 44 additions & 0 deletions taichi/backends/cc/runtime/base.h
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Expand Up @@ -83,6 +83,50 @@ static inline Ti_f32 Ti_rand_f32(void) {
return (Ti_f32) drand48(); // [0.0, 1.0)
}

// Copied from Metal:
typedef Ti_u8 *Ti_AdStackPtr;

static inline Ti_u32 *Ti_ad_stack_n(Ti_AdStackPtr stack) {
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Well... I would suggest not using a capital letter as the beginning of a function's name. I haven't taken a look at the C backend before, so is there any reason that the Ti_ prefix is used? I would suggest cc_ prefix to show that it's the C backend (and probably Cc for classes).

return (Ti_u32 *)stack;
}

static inline Ti_AdStackPtr Ti_ad_stack_data(Ti_AdStackPtr stack) {
return stack + sizeof(Ti_u32);
}

static inline void Ti_ad_stack_init(Ti_AdStackPtr stack) {
Ti_u32 *n = Ti_ad_stack_n(stack);
Ti_i32 *data = (Ti_i32 *)Ti_ad_stack_data(stack);
*n = 0;
}

static inline Ti_AdStackPtr Ti_ad_stack_top_primal(Ti_AdStackPtr stack,
Ti_u32 element_size) {
Ti_u32 *n = Ti_ad_stack_n(stack);
return Ti_ad_stack_data(stack) + (*n - 1) * 2 * element_size;
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@archibate archibate Aug 23, 2020 •
edited
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I copied from ad_stack.metal.h, can you tell me why n - 1 here? @k-ye
Sometimes n can be 0 and it gets overflowed, resulting in a serious segfault when the lhs pointer is 64-bit (-1 = 0xffffffff). But it somehow silently passed on Metal whose pointer is 32-bit?

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I think when n is 0, it's pretty OK to have a segfault here -- just like this in C++:

std::stack<int> s;
s.top();  // runtime error

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Exactly, this is just l[len(l) - 1]. As mentioned, accessing top without push sounds like a bug.

}

static inline Ti_AdStackPtr Ti_ad_stack_top_adjoint(Ti_AdStackPtr stack,
Ti_u32 element_size) {
return Ti_ad_stack_top_primal(stack, element_size) + element_size;
}

static inline void Ti_ad_stack_pop(Ti_AdStackPtr stack) {
Ti_u32 *n = Ti_ad_stack_n(stack);
--(*n);
}

static inline void Ti_ad_stack_push(Ti_AdStackPtr stack, Ti_u32 element_size) {
Ti_u32 i;
Ti_u32 *n = Ti_ad_stack_n(stack);
++(*n);

Ti_AdStackPtr data = Ti_ad_stack_top_primal(stack, element_size);
for (i = 0; i < element_size * 2; ++i) {
data[i] = 0;
}
}

) "\n" STR(
)

Expand Down
2 changes: 1 addition & 1 deletion taichi/program/extension.cpp
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Expand Up @@ -19,7 +19,7 @@ bool is_extension_supported(Arch arch, Extension ext) {
Extension::adstack, Extension::bls, Extension::assertion}},
{Arch::metal, {Extension::adstack}},
{Arch::opengl, {Extension::extfunc}},
{Arch::cc, {Extension::data64, Extension::extfunc}},
{Arch::cc, {Extension::data64, Extension::extfunc, Extension::adstack}},
};
// if (with_opengl_extension_data64())
// arch2ext[Arch::opengl].insert(Extension::data64); // TODO: singleton
Expand Down