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Force operator< to be inlined to reduce place time #1265

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Merged
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Apr 13, 2020
Merged

Force operator< to be inlined to reduce place time #1265

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36 changes: 33 additions & 3 deletions vpr/src/place/place_delay_model.h
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,20 @@
#include "vpr_types.h"
#include "router_delay_profiling.h"

#ifndef __has_attribute
# define __has_attribute(x) 0 // Compatibility with non-clang compilers.
#endif

#if defined(COMPILER_GCC) && defined(NDEBUG)
# define ALWAYS_INLINE inline __attribute__((__always_inline__))
#elif defined(COMPILER_MSVC) && defined(NDEBUG)
# define ALWAYS_INLINE __forceinline
#elif __has_attribute(always_inline)
# define ALWAYS_INLINE __attribute__((always_inline)) // clang
#else
# define ALWAYS_INLINE inline
#endif

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I wonder if it would be better to use C++ attributes (available since C++11) as a cleaner way to specify this.

For example:

[[gnu::always_inline]] friend bool operator<(const t_override& lhs, const t_override& rhs) {

That would avoid having to define the ALWAYS_INLINE macro in a cleaner cross-compiler way.

@mithro Any thoughts on this?

//Abstract interface to a placement delay model
class PlaceDelayModel {
public:
Expand Down Expand Up @@ -95,13 +109,29 @@ class OverrideDelayModel : public PlaceDelayModel {
short delta_x;
short delta_y;

friend bool operator<(const t_override& lhs, const t_override& rhs) {
return std::tie(lhs.from_type, lhs.to_type, lhs.from_class, lhs.to_class, lhs.delta_x, lhs.delta_y)
< std::tie(rhs.from_type, rhs.to_type, rhs.from_class, rhs.to_class, rhs.delta_x, rhs.delta_y);
//A combination of ALWAYS_INLINE attribute and std::lexicographical_compare
//is required for operator< to be inlined by compiler.
//Proper inlining of the function reduces place time by around 5%.
//For more information: https://github.com/verilog-to-routing/vtr-verilog-to-routing/issues/1225
friend ALWAYS_INLINE bool operator<(const t_override& lhs, const t_override& rhs) {
const short* left = reinterpret_cast<const short*>(&lhs);
const short* right = reinterpret_cast<const short*>(&rhs);
constexpr size_t NUM_T_OVERRIDE_MEMBERS = sizeof(t_override) / sizeof(short);
return std::lexicographical_compare(left, left + NUM_T_OVERRIDE_MEMBERS, right, right + NUM_T_OVERRIDE_MEMBERS);
}
};

vtr::flat_map2<t_override, float> delay_overrides_;

//operator< treats memory layout of t_override as an array of short
//this requires all members of t_override are shorts and there is no padding between members of t_override
static_assert(sizeof(t_override) == sizeof(t_override::from_type) + sizeof(t_override::to_type) + sizeof(t_override::from_class) + sizeof(t_override::to_class) + sizeof(t_override::delta_x) + sizeof(t_override::delta_y), "Expect t_override to have a memory layout equivalent to an array of short (no padding)");
static_assert(sizeof(t_override::from_type) == sizeof(short), "Expect all t_override data members to be shorts");
static_assert(sizeof(t_override::to_type) == sizeof(short), "Expect all t_override data members to be shorts");
static_assert(sizeof(t_override::from_class) == sizeof(short), "Expect all t_override data members to be shorts");
static_assert(sizeof(t_override::to_class) == sizeof(short), "Expect all t_override data members to be shorts");
static_assert(sizeof(t_override::delta_x) == sizeof(short), "Expect all t_override data members to be shorts");
static_assert(sizeof(t_override::delta_y) == sizeof(short), "Expect all t_override data members to be shorts");
};

#endif