Disable Function Optimization with Attribute

Single function definition

Clang

// Clang
// GNU-style attribute
__attribute__((optnone))
int foo(){}
// C++11 attribute
[[clang::optnone]]
int foo(){}

GCC

__attribute__((optimize("O0")))
int foo(){}

Multiply function definition

Clang

#pragma clang optimize off
// This function will be decorated with optnone.
int foo() {}
 
// optnone conflicts with always_inline, so bar() will not be decorated.
__attribute__((always_inline)) int bar(){}
#pragma clang optimize on

Visual Studio

#pragma optimize( "", off )
/* unoptimized code section */
#pragma optimize( "", on )

GCC

#pragma GCC push_options
#pragma GCC optimize("O0")
/* unoptimized code section */
#pragma GCC pop_options

Reference

Clang Language Extensions — Clang 8 documentation (bcain-llvm.readthedocs.io)
optimize pragma | Microsoft Learn
[Tutorial] GCC Optimization Pragmas - Codeforces