Disabling some of MSVC most aggressive Debug runtime checks for some simple/low-level functions

(e.g. ImVec2, ImVector) leading to a 10-20% increase of performances with MSVC "default" Debug settings.

docs/CHANGELOG.txt

@@ -61,6 +61,8 @@ Other Changes:
 - LabelText: Fixed clipping of multi-line value text when label is single-line. (#4004)
 - LabelText: Fixed vertical alignment of single-line value text when label is multi-line. (#4004)
 - Popups: Added 'OpenPopup(ImGuiID id)' overload to facilitate calling from nested stacks. (#3993, #331) [@zlash]
+- Optimization: Disabling some of MSVC most aggressive Debug runtime checks for some simple/low-level functions
+  (e.g. ImVec2, ImVector) leading to a 10-20% increase of performances with MSVC "default" Debug settings.
 - ImDrawList: Fixed/improved thickness of thick strokes with sharp angles. (#4053, #3366, #2964, #2868, #2518, #2183)
   Effectively introduced a regression in 1.67 (Jan 2019), and a fix in 1.70 (Apr 2019) but the fix wasn't actually on
   par with original version. Now incorporating the correct revert.

imgui.h

@@ -100,6 +100,15 @@ Index of this file:
 #define IM_FMTLIST(FMT)
 #endif
 
+// Disable some of MSVC most aggressive Debug runtime checks in function header/footer (used in some simple/low-level functions)
+#if defined(_MSC_VER) && !defined(__clang__) && !defined(IMGUI_DEBUG_PARANOID)
+#define IM_MSVC_RUNTIME_CHECKS_OFF      __pragma(runtime_checks("",off))     __pragma(check_stack(off)) __pragma(strict_gs_check(push,off))
+#define IM_MSVC_RUNTIME_CHECKS_RESTORE  __pragma(runtime_checks("",restore)) __pragma(check_stack())    __pragma(strict_gs_check(pop))
+#else
+#define IM_MSVC_RUNTIME_CHECKS_OFF
+#define IM_MSVC_RUNTIME_CHECKS_RESTORE
+#endif
+
 // Warnings
 #ifdef _MSC_VER
 #pragma warning (push)
@@ -231,6 +240,7 @@ typedef unsigned long long  ImU64;  // 64-bit unsigned integer (post C++11)
 #endif
 
 // 2D vector (often used to store positions or sizes)
+IM_MSVC_RUNTIME_CHECKS_OFF
 struct ImVec2
 {
     float                                   x, y;
@@ -253,6 +263,7 @@ struct ImVec4
     IM_VEC4_CLASS_EXTRA     // Define additional constructors and implicit cast operators in imconfig.h to convert back and forth between your math types and ImVec4.
 #endif
 };
+IM_MSVC_RUNTIME_CHECKS_RESTORE
 
 //-----------------------------------------------------------------------------
 // [SECTION] Dear ImGui end-user API functions
@@ -1637,6 +1648,7 @@ template<typename T> void IM_DELETE(T* p)   { if (p) { p->~T(); ImGui::MemFree(p
 //   Do NOT use this class as a std::vector replacement in your own code! Many of the structures used by dear imgui can be safely initialized by a zero-memset.
 //-----------------------------------------------------------------------------
 
+IM_MSVC_RUNTIME_CHECKS_OFF
 template<typename T>
 struct ImVector
 {
@@ -1695,6 +1707,7 @@ struct ImVector
     inline bool         find_erase_unsorted(const T& v)     { const T* it = find(v); if (it < Data + Size) { erase_unsorted(it); return true; } return false; }
     inline int          index_from_ptr(const T* it) const   { IM_ASSERT(it >= Data && it < Data + Size); const ptrdiff_t off = it - Data; return (int)off; }
 };
+IM_MSVC_RUNTIME_CHECKS_RESTORE
 
 //-----------------------------------------------------------------------------
 // [SECTION] ImGuiStyle

imgui_internal.h

@@ -326,6 +326,7 @@ IMGUI_API int           ImTextCountUtf8BytesFromStr(const ImWchar* in_text, cons
 // We are keeping those disabled by default so they don't leak in user space, to allow user enabling implicit cast operators between ImVec2 and their own types (using IM_VEC2_CLASS_EXTRA etc.)
 // We unfortunately don't have a unary- operator for ImVec2 because this would needs to be defined inside the class itself.
 #ifdef IMGUI_DEFINE_MATH_OPERATORS
+IM_MSVC_RUNTIME_CHECKS_OFF
 static inline ImVec2 operator*(const ImVec2& lhs, const float rhs)              { return ImVec2(lhs.x * rhs, lhs.y * rhs); }
 static inline ImVec2 operator/(const ImVec2& lhs, const float rhs)              { return ImVec2(lhs.x / rhs, lhs.y / rhs); }
 static inline ImVec2 operator+(const ImVec2& lhs, const ImVec2& rhs)            { return ImVec2(lhs.x + rhs.x, lhs.y + rhs.y); }
@@ -341,6 +342,7 @@ static inline ImVec2& operator/=(ImVec2& lhs, const ImVec2& rhs)
 static inline ImVec4 operator+(const ImVec4& lhs, const ImVec4& rhs)            { return ImVec4(lhs.x + rhs.x, lhs.y + rhs.y, lhs.z + rhs.z, lhs.w + rhs.w); }
 static inline ImVec4 operator-(const ImVec4& lhs, const ImVec4& rhs)            { return ImVec4(lhs.x - rhs.x, lhs.y - rhs.y, lhs.z - rhs.z, lhs.w - rhs.w); }
 static inline ImVec4 operator*(const ImVec4& lhs, const ImVec4& rhs)            { return ImVec4(lhs.x * rhs.x, lhs.y * rhs.y, lhs.z * rhs.z, lhs.w * rhs.w); }
+IM_MSVC_RUNTIME_CHECKS_RESTORE
 #endif
 
 // Helpers: File System
@@ -366,6 +368,7 @@ IMGUI_API ImU64             ImFileWrite(const void* data, ImU64 size, ImU64 coun
 IMGUI_API void*             ImFileLoadToMemory(const char* filename, const char* mode, size_t* out_file_size = NULL, int padding_bytes = 0);
 
 // Helpers: Maths
+IM_MSVC_RUNTIME_CHECKS_OFF
 // - Wrapper for standard libs functions. (Note that imgui_demo.cpp does _not_ use them to keep the code easy to copy)
 #ifndef IMGUI_DISABLE_DEFAULT_MATH_FUNCTIONS
 #define ImFabs(X)           fabsf(X)
@@ -416,6 +419,7 @@ static inline float  ImDot(const ImVec2& a, const ImVec2& b)
 static inline ImVec2 ImRotate(const ImVec2& v, float cos_a, float sin_a)        { return ImVec2(v.x * cos_a - v.y * sin_a, v.x * sin_a + v.y * cos_a); }
 static inline float  ImLinearSweep(float current, float target, float speed)    { if (current < target) return ImMin(current + speed, target); if (current > target) return ImMax(current - speed, target); return current; }
 static inline ImVec2 ImMul(const ImVec2& lhs, const ImVec2& rhs)                { return ImVec2(lhs.x * rhs.x, lhs.y * rhs.y); }
+IM_MSVC_RUNTIME_CHECKS_RESTORE
 
 // Helpers: Geometry
 IMGUI_API ImVec2     ImBezierCubicCalc(const ImVec2& p1, const ImVec2& p2, const ImVec2& p3, const ImVec2& p4, float t);
@@ -431,6 +435,7 @@ IMGUI_API ImGuiDir   ImGetDirQuadrantFromDelta(float dx, float dy);
 
 // Helper: ImVec1 (1D vector)
 // (this odd construct is used to facilitate the transition between 1D and 2D, and the maintenance of some branches/patches)
+IM_MSVC_RUNTIME_CHECKS_OFF
 struct ImVec1
 {
     float   x;
@@ -484,6 +489,7 @@ struct IMGUI_API ImRect
     bool        IsInverted() const                  { return Min.x > Max.x || Min.y > Max.y; }
     ImVec4      ToVec4() const                      { return ImVec4(Min.x, Min.y, Max.x, Max.y); }
 };
+IM_MSVC_RUNTIME_CHECKS_RESTORE
 
 // Helper: ImBitArray
 inline bool     ImBitArrayTestBit(const ImU32* arr, int n)      { ImU32 mask = (ImU32)1 << (n & 31); return (arr[n >> 5] & mask) != 0; }