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The proposal P0595R1, as it is currently stated, in my opinion, would be a
wonderful addition to C++. However I believe that there could be another
potential use case for std::is_constant_evaluated, in which it accepts a
variable as an argument. The expression would return true if and only if
the compiler is already aware of the value of the variable itself. The
motivation behind this is to address proposals for constexpr variable
function arguments and similar situations, but could sidestep the potential
pitfalls of function overloading. But it allows the programmer to leverage
inline optimizations that the compiler is often already doing by making
him/her aware of when those optimizations are applied.

Declared something like this:
namespace std
{
    // Already in P0595R1. This returns true if the compiler is evaluating
the function itself in constexpr context.
    constexpr bool is_constant_evaluated() noexcept;


    // Returns true if the literal value of variable t is known to the
compiler.
    template <typename T>
    constexpr bool is_constant_evaluated(T t) noexcept;
}


Example usage:
inline constexpr float MyPow(float x, float y)
{
    if constexpr (std::is_constant_evaluated())
    {
        return 0; // TODO: Make a compile-time friendly pow function
    }
    else if constexpr (std::is_constant_evaluated(y))
    {
        if constexpr (y == 0.f)
            return 1.f;
        if constexpr (y == 1.f)
            return x;
        if constexpr (y == 2.f)
            return x * x;
        if constexpr (y == 3.f)
            return x * x * x;
        else
            return powf(x, y);
    }
    else
        return powf(x, y);
}


float g_x, g_y; // globally mutable, always evaluated at runtime
int main()
{
    constexpr float a = MyPow(3.14f, 2.5f); // MyPow takes the first if
block and returns a value computed at compile-time
    float b = MyPow(g_x, 2.0f);             // Compiler inlines: float b =
g_x * g_x;
    float c = MyPow(g_x, 1.0f);             // Compiler inlines: float c =
g_x;
    float d = MyPow(g_x, g_y);              // Compiler inlines: float d =
powf(g_x, g_y);


    float y = 0.f;
    float e = MyPow(g_x, y);                // Optimizing compiler SHOULD
inline: float e = 1.0f; Because y is known at compile time.


    return 0;
}


This of course makes the assumption that the compiler is obligated to skip
compilation of code that fails the constexpr if conditional where it would
instead compile the code in the else blocks, and vice versa where the if
constexpr passes. It's also worth mentioning that there should be no
guarantee that just because a variable is assigned to a literal and then
immediately queried for std::is_constant_evaluated that it will return
true. It's up to the compiler to respect this case only when the variable
is optimized in a way to be treated as such. For example, it may return
false in a non-optimized build, but true in an optimized build where inline
expansion is guaranteed.

As far as the preceding example goes, yes, I went straight to the float use
case, which is normally non-integral, but I wanted to also demonstrate that
this works around the issue where floats cannot be template arguments in a
more elegant and uniformly obvious way where a function author can optimize
for specific cases and combinations of literal values.

--
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<div dir=3D"ltr">The proposal P0595R1, as it is currently stated, in my opi=
nion, would be a wonderful addition to C++. However I believe that there co=
uld be another potential use case for std::is_constant_evaluated, in which =
it accepts a variable as an argument. The expression would return true if a=
nd only if the compiler is already aware of the value of the variable itsel=
f. The motivation behind this is to address proposals for constexpr variabl=
e function arguments and similar situations, but could sidestep the potenti=
al pitfalls of function overloading. But it allows the programmer to levera=
ge inline optimizations that the compiler is often already doing by making =
him/her aware of when those optimizations are applied.<div><br></div><div><=
div>Declared something like this:</div><div><div class=3D"prettyprint" styl=
e=3D"background-color: rgb(250, 250, 250); border-color: rgb(187, 187, 187)=
; border-style: solid; border-width: 1px; word-wrap: break-word;"><code cla=
ss=3D"prettyprint"><div class=3D"subprettyprint"><span style=3D"color: #008=
;" class=3D"styled-by-prettify">namespace</span><span style=3D"color: #000;=
" class=3D"styled-by-prettify"> std<br></span><span style=3D"color: #660;" =
class=3D"styled-by-prettify">{</span><span style=3D"color: #000;" class=3D"=
styled-by-prettify"><br>=C2=A0 =C2=A0 </span><span style=3D"color: #800;" c=
lass=3D"styled-by-prettify">// Already in P0595R1. This returns true if the=
 compiler is evaluating the function itself in constexpr context.</span><sp=
an style=3D"color: #000;" class=3D"styled-by-prettify"><br>=C2=A0 =C2=A0 </=
span><span style=3D"color: #008;" class=3D"styled-by-prettify">constexpr</s=
pan><span style=3D"color: #000;" class=3D"styled-by-prettify"> </span><span=
 style=3D"color: #008;" class=3D"styled-by-prettify">bool</span><span style=
=3D"color: #000;" class=3D"styled-by-prettify"> is_constant_evaluated</span=
><span style=3D"color: #660;" class=3D"styled-by-prettify">()</span><span s=
tyle=3D"color: #000;" class=3D"styled-by-prettify"> noexcept</span><span st=
yle=3D"color: #660;" class=3D"styled-by-prettify">;</span><span style=3D"co=
lor: #000;" class=3D"styled-by-prettify"><br><br><br>=C2=A0 =C2=A0 </span><=
span style=3D"color: #800;" class=3D"styled-by-prettify">// Returns true if=
 the literal value of variable t is known to the compiler.</span><span styl=
e=3D"color: #000;" class=3D"styled-by-prettify"><br>=C2=A0 =C2=A0 </span><s=
pan style=3D"color: #008;" class=3D"styled-by-prettify">template</span><spa=
n style=3D"color: #000;" class=3D"styled-by-prettify"> </span><span style=
=3D"color: #660;" class=3D"styled-by-prettify">&lt;</span><span style=3D"co=
lor: #008;" class=3D"styled-by-prettify">typename</span><span style=3D"colo=
r: #000;" class=3D"styled-by-prettify"> T</span><span style=3D"color: #660;=
" class=3D"styled-by-prettify">&gt;</span><span style=3D"color: #000;" clas=
s=3D"styled-by-prettify"><br>=C2=A0 =C2=A0 </span><span style=3D"color: #00=
8;" class=3D"styled-by-prettify">constexpr</span><span style=3D"color: #000=
;" class=3D"styled-by-prettify"> </span><span style=3D"color: #008;" class=
=3D"styled-by-prettify">bool</span><span style=3D"color: #000;" class=3D"st=
yled-by-prettify"> is_constant_evaluated</span><span style=3D"color: #660;"=
 class=3D"styled-by-prettify">(</span><span style=3D"color: #000;" class=3D=
"styled-by-prettify">T t</span><span style=3D"color: #660;" class=3D"styled=
-by-prettify">)</span><span style=3D"color: #000;" class=3D"styled-by-prett=
ify"> noexcept</span><span style=3D"color: #660;" class=3D"styled-by-pretti=
fy">;</span><span style=3D"color: #000;" class=3D"styled-by-prettify"><br><=
/span><span style=3D"color: #660;" class=3D"styled-by-prettify">}</span></d=
iv></code></div><div><br></div></div><div><br></div><div>Example usage:</di=
v></div><div><div class=3D"prettyprint" style=3D"background-color: rgb(250,=
 250, 250); border-color: rgb(187, 187, 187); border-style: solid; border-w=
idth: 1px; word-wrap: break-word;"><code class=3D"prettyprint"><div class=
=3D"subprettyprint"><span style=3D"color: #008;" class=3D"styled-by-prettif=
y">inline</span><span style=3D"color: #000;" class=3D"styled-by-prettify"> =
</span><span style=3D"color: #008;" class=3D"styled-by-prettify">constexpr<=
/span><span style=3D"color: #000;" class=3D"styled-by-prettify"> </span><sp=
an style=3D"color: #008;" class=3D"styled-by-prettify">float</span><span st=
yle=3D"color: #000;" class=3D"styled-by-prettify"> </span><span style=3D"co=
lor: #606;" class=3D"styled-by-prettify">MyPow</span><span style=3D"color: =
#660;" class=3D"styled-by-prettify">(</span><span style=3D"color: #008;" cl=
ass=3D"styled-by-prettify">float</span><span style=3D"color: #000;" class=
=3D"styled-by-prettify"> x</span><span style=3D"color: #660;" class=3D"styl=
ed-by-prettify">,</span><span style=3D"color: #000;" class=3D"styled-by-pre=
ttify"> </span><span style=3D"color: #008;" class=3D"styled-by-prettify">fl=
oat</span><span style=3D"color: #000;" class=3D"styled-by-prettify"> y</spa=
n><span style=3D"color: #660;" class=3D"styled-by-prettify">)</span><span s=
tyle=3D"color: #000;" class=3D"styled-by-prettify"><br></span><span style=
=3D"color: #660;" class=3D"styled-by-prettify">{</span><span style=3D"color=
: #000;" class=3D"styled-by-prettify"><br>=C2=A0 =C2=A0 </span><span style=
=3D"color: #008;" class=3D"styled-by-prettify">if</span><span style=3D"colo=
r: #000;" class=3D"styled-by-prettify"> </span><span style=3D"color: #008;"=
 class=3D"styled-by-prettify">constexpr</span><span style=3D"color: #000;" =
class=3D"styled-by-prettify"> </span><span style=3D"color: #660;" class=3D"=
styled-by-prettify">(</span><span style=3D"color: #000;" class=3D"styled-by=
-prettify">std</span><span style=3D"color: #660;" class=3D"styled-by-pretti=
fy">::</span><span style=3D"color: #000;" class=3D"styled-by-prettify">is_c=
onstant_evaluated</span><span style=3D"color: #660;" class=3D"styled-by-pre=
ttify">())</span><span style=3D"color: #000;" class=3D"styled-by-prettify">=
<br>=C2=A0 =C2=A0 </span><span style=3D"color: #660;" class=3D"styled-by-pr=
ettify">{</span><span style=3D"color: #000;" class=3D"styled-by-prettify"><=
br>=C2=A0 =C2=A0 =C2=A0 =C2=A0 </span><span style=3D"color: #008;" class=3D=
"styled-by-prettify">return</span><span style=3D"color: #000;" class=3D"sty=
led-by-prettify"> </span><span style=3D"color: #066;" class=3D"styled-by-pr=
ettify">0</span><span style=3D"color: #660;" class=3D"styled-by-prettify">;=
</span><span style=3D"color: #000;" class=3D"styled-by-prettify"> </span><s=
pan style=3D"color: #800;" class=3D"styled-by-prettify">// TODO: Make a com=
pile-time friendly pow function</span><span style=3D"color: #000;" class=3D=
"styled-by-prettify"><br>=C2=A0 =C2=A0 </span><span style=3D"color: #660;" =
class=3D"styled-by-prettify">}</span><span style=3D"color: #000;" class=3D"=
styled-by-prettify"><br>=C2=A0 =C2=A0 </span><span style=3D"color: #008;" c=
lass=3D"styled-by-prettify">else</span><span style=3D"color: #000;" class=
=3D"styled-by-prettify"> </span><span style=3D"color: #008;" class=3D"style=
d-by-prettify">if</span><span style=3D"color: #000;" class=3D"styled-by-pre=
ttify"> </span><span style=3D"color: #008;" class=3D"styled-by-prettify">co=
nstexpr</span><span style=3D"color: #000;" class=3D"styled-by-prettify"> </=
span><span style=3D"color: #660;" class=3D"styled-by-prettify">(</span><spa=
n style=3D"color: #000;" class=3D"styled-by-prettify">std</span><span style=
=3D"color: #660;" class=3D"styled-by-prettify">::</span><span style=3D"colo=
r: #000;" class=3D"styled-by-prettify">is_constant_evaluated</span><span st=
yle=3D"color: #660;" class=3D"styled-by-prettify">(</span><span style=3D"co=
lor: #000;" class=3D"styled-by-prettify">y</span><span style=3D"color: #660=
;" class=3D"styled-by-prettify">))</span><span style=3D"color: #000;" class=
=3D"styled-by-prettify"><br>=C2=A0 =C2=A0 </span><span style=3D"color: #660=
;" class=3D"styled-by-prettify">{</span><span style=3D"color: #000;" class=
=3D"styled-by-prettify"><br>=C2=A0 =C2=A0 =C2=A0 =C2=A0 </span><span style=
=3D"color: #008;" class=3D"styled-by-prettify">if</span><span style=3D"colo=
r: #000;" class=3D"styled-by-prettify"> </span><span style=3D"color: #008;"=
 class=3D"styled-by-prettify">constexpr</span><span style=3D"color: #000;" =
class=3D"styled-by-prettify"> </span><span style=3D"color: #660;" class=3D"=
styled-by-prettify">(</span><span style=3D"color: #000;" class=3D"styled-by=
-prettify">y </span><span style=3D"color: #660;" class=3D"styled-by-prettif=
y">=3D=3D</span><span style=3D"color: #000;" class=3D"styled-by-prettify"> =
</span><span style=3D"color: #066;" class=3D"styled-by-prettify">0.f</span>=
<span style=3D"color: #660;" class=3D"styled-by-prettify">)</span><span sty=
le=3D"color: #000;" class=3D"styled-by-prettify"><br>=C2=A0 =C2=A0 =C2=A0 =
=C2=A0 =C2=A0 =C2=A0 </span><span style=3D"color: #008;" class=3D"styled-by=
-prettify">return</span><span style=3D"color: #000;" class=3D"styled-by-pre=
ttify"> </span><span style=3D"color: #066;" class=3D"styled-by-prettify">1.=
f</span><span style=3D"color: #660;" class=3D"styled-by-prettify">;</span><=
span style=3D"color: #000;" class=3D"styled-by-prettify"><br>=C2=A0 =C2=A0 =
=C2=A0 =C2=A0 </span><span style=3D"color: #008;" class=3D"styled-by-pretti=
fy">if</span><span style=3D"color: #000;" class=3D"styled-by-prettify"> </s=
pan><span style=3D"color: #008;" class=3D"styled-by-prettify">constexpr</sp=
an><span style=3D"color: #000;" class=3D"styled-by-prettify"> </span><span =
style=3D"color: #660;" class=3D"styled-by-prettify">(</span><span style=3D"=
color: #000;" class=3D"styled-by-prettify">y </span><span style=3D"color: #=
660;" class=3D"styled-by-prettify">=3D=3D</span><span style=3D"color: #000;=
" class=3D"styled-by-prettify"> </span><span style=3D"color: #066;" class=
=3D"styled-by-prettify">1.f</span><span style=3D"color: #660;" class=3D"sty=
led-by-prettify">)</span><span style=3D"color: #000;" class=3D"styled-by-pr=
ettify"><br>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 </span><span style=3D=
"color: #008;" class=3D"styled-by-prettify">return</span><span style=3D"col=
or: #000;" class=3D"styled-by-prettify"> x</span><span style=3D"color: #660=
;" class=3D"styled-by-prettify">;</span><span style=3D"color: #000;" class=
=3D"styled-by-prettify"><br>=C2=A0 =C2=A0 =C2=A0 =C2=A0 </span><span style=
=3D"color: #008;" class=3D"styled-by-prettify">if</span><span style=3D"colo=
r: #000;" class=3D"styled-by-prettify"> </span><span style=3D"color: #008;"=
 class=3D"styled-by-prettify">constexpr</span><span style=3D"color: #000;" =
class=3D"styled-by-prettify"> </span><span style=3D"color: #660;" class=3D"=
styled-by-prettify">(</span><span style=3D"color: #000;" class=3D"styled-by=
-prettify">y </span><span style=3D"color: #660;" class=3D"styled-by-prettif=
y">=3D=3D</span><span style=3D"color: #000;" class=3D"styled-by-prettify"> =
</span><span style=3D"color: #066;" class=3D"styled-by-prettify">2.f</span>=
<span style=3D"color: #660;" class=3D"styled-by-prettify">)</span><span sty=
le=3D"color: #000;" class=3D"styled-by-prettify"><br>=C2=A0 =C2=A0 =C2=A0 =
=C2=A0 =C2=A0 =C2=A0 </span><span style=3D"color: #008;" class=3D"styled-by=
-prettify">return</span><span style=3D"color: #000;" class=3D"styled-by-pre=
ttify"> x </span><span style=3D"color: #660;" class=3D"styled-by-prettify">=
*</span><span style=3D"color: #000;" class=3D"styled-by-prettify"> x</span>=
<span style=3D"color: #660;" class=3D"styled-by-prettify">;</span><span sty=
le=3D"color: #000;" class=3D"styled-by-prettify"><br>=C2=A0 =C2=A0 =C2=A0 =
=C2=A0 </span><span style=3D"color: #008;" class=3D"styled-by-prettify">if<=
/span><span style=3D"color: #000;" class=3D"styled-by-prettify"> </span><sp=
an style=3D"color: #008;" class=3D"styled-by-prettify">constexpr</span><spa=
n style=3D"color: #000;" class=3D"styled-by-prettify"> </span><span style=
=3D"color: #660;" class=3D"styled-by-prettify">(</span><span style=3D"color=
: #000;" class=3D"styled-by-prettify">y </span><span style=3D"color: #660;"=
 class=3D"styled-by-prettify">=3D=3D</span><span style=3D"color: #000;" cla=
ss=3D"styled-by-prettify"> </span><span style=3D"color: #066;" class=3D"sty=
led-by-prettify">3.f</span><span style=3D"color: #660;" class=3D"styled-by-=
prettify">)</span><span style=3D"color: #000;" class=3D"styled-by-prettify"=
><br>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 </span><span style=3D"color:=
 #008;" class=3D"styled-by-prettify">return</span><span style=3D"color: #00=
0;" class=3D"styled-by-prettify"> x </span><span style=3D"color: #660;" cla=
ss=3D"styled-by-prettify">*</span><span style=3D"color: #000;" class=3D"sty=
led-by-prettify"> x </span><span style=3D"color: #660;" class=3D"styled-by-=
prettify">*</span><span style=3D"color: #000;" class=3D"styled-by-prettify"=
> x</span><span style=3D"color: #660;" class=3D"styled-by-prettify">;</span=
><span style=3D"color: #000;" class=3D"styled-by-prettify"><br>=C2=A0 =C2=
=A0 =C2=A0 =C2=A0 </span><span style=3D"color: #008;" class=3D"styled-by-pr=
ettify">else</span><span style=3D"color: #000;" class=3D"styled-by-prettify=
"><br>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 </span><span style=3D"color=
: #008;" class=3D"styled-by-prettify">return</span><span style=3D"color: #0=
00;" class=3D"styled-by-prettify"> powf</span><span style=3D"color: #660;" =
class=3D"styled-by-prettify">(</span><span style=3D"color: #000;" class=3D"=
styled-by-prettify">x</span><span style=3D"color: #660;" class=3D"styled-by=
-prettify">,</span><span style=3D"color: #000;" class=3D"styled-by-prettify=
"> y</span><span style=3D"color: #660;" class=3D"styled-by-prettify">);</sp=
an><span style=3D"color: #000;" class=3D"styled-by-prettify"><br>=C2=A0 =C2=
=A0 </span><span style=3D"color: #660;" class=3D"styled-by-prettify">}</spa=
n><span style=3D"color: #000;" class=3D"styled-by-prettify"><br>=C2=A0 =C2=
=A0 </span><span style=3D"color: #008;" class=3D"styled-by-prettify">else</=
span><span style=3D"color: #000;" class=3D"styled-by-prettify"><br>=C2=A0 =
=C2=A0 =C2=A0 =C2=A0 </span><span style=3D"color: #008;" class=3D"styled-by=
-prettify">return</span><span style=3D"color: #000;" class=3D"styled-by-pre=
ttify"> powf</span><span style=3D"color: #660;" class=3D"styled-by-prettify=
">(</span><span style=3D"color: #000;" class=3D"styled-by-prettify">x</span=
><span style=3D"color: #660;" class=3D"styled-by-prettify">,</span><span st=
yle=3D"color: #000;" class=3D"styled-by-prettify"> y</span><span style=3D"c=
olor: #660;" class=3D"styled-by-prettify">);</span><span style=3D"color: #0=
00;" class=3D"styled-by-prettify"><br></span><span style=3D"color: #660;" c=
lass=3D"styled-by-prettify">}</span><span style=3D"color: #000;" class=3D"s=
tyled-by-prettify"><br><br><br></span><span style=3D"color: #008;" class=3D=
"styled-by-prettify">float</span><span style=3D"color: #000;" class=3D"styl=
ed-by-prettify"> g_x</span><span style=3D"color: #660;" class=3D"styled-by-=
prettify">,</span><span style=3D"color: #000;" class=3D"styled-by-prettify"=
> g_y</span><span style=3D"color: #660;" class=3D"styled-by-prettify">;</sp=
an><span style=3D"color: #000;" class=3D"styled-by-prettify"> </span><span =
style=3D"color: #800;" class=3D"styled-by-prettify">// globally mutable, al=
ways evaluated at runtime</span><span style=3D"color: #000;" class=3D"style=
d-by-prettify"><br></span><span style=3D"color: #008;" class=3D"styled-by-p=
rettify">int</span><span style=3D"color: #000;" class=3D"styled-by-prettify=
"> main</span><span style=3D"color: #660;" class=3D"styled-by-prettify">()<=
/span><span style=3D"color: #000;" class=3D"styled-by-prettify"><br></span>=
<span style=3D"color: #660;" class=3D"styled-by-prettify">{</span><span sty=
le=3D"color: #000;" class=3D"styled-by-prettify"><br>=C2=A0 =C2=A0 </span><=
span style=3D"color: #008;" class=3D"styled-by-prettify">constexpr</span><s=
pan style=3D"color: #000;" class=3D"styled-by-prettify"> </span><span style=
=3D"color: #008;" class=3D"styled-by-prettify">float</span><span style=3D"c=
olor: #000;" class=3D"styled-by-prettify"> a </span><span style=3D"color: #=
660;" class=3D"styled-by-prettify">=3D</span><span style=3D"color: #000;" c=
lass=3D"styled-by-prettify"> </span><span style=3D"color: #606;" class=3D"s=
tyled-by-prettify">MyPow</span><span style=3D"color: #660;" class=3D"styled=
-by-prettify">(</span><span style=3D"color: #066;" class=3D"styled-by-prett=
ify">3.14f</span><span style=3D"color: #660;" class=3D"styled-by-prettify">=
,</span><span style=3D"color: #000;" class=3D"styled-by-prettify"> </span><=
span style=3D"color: #066;" class=3D"styled-by-prettify">2.5f</span><span s=
tyle=3D"color: #660;" class=3D"styled-by-prettify">);</span><span style=3D"=
color: #000;" class=3D"styled-by-prettify"> </span><span style=3D"color: #8=
00;" class=3D"styled-by-prettify">// MyPow takes the first if block and ret=
urns a value computed at compile-time</span><span style=3D"color: #000;" cl=
ass=3D"styled-by-prettify"><br>=C2=A0 =C2=A0 </span><span style=3D"color: #=
008;" class=3D"styled-by-prettify">float</span><span style=3D"color: #000;"=
 class=3D"styled-by-prettify"> b </span><span style=3D"color: #660;" class=
=3D"styled-by-prettify">=3D</span><span style=3D"color: #000;" class=3D"sty=
led-by-prettify"> </span><span style=3D"color: #606;" class=3D"styled-by-pr=
ettify">MyPow</span><span style=3D"color: #660;" class=3D"styled-by-prettif=
y">(</span><span style=3D"color: #000;" class=3D"styled-by-prettify">g_x</s=
pan><span style=3D"color: #660;" class=3D"styled-by-prettify">,</span><span=
 style=3D"color: #000;" class=3D"styled-by-prettify"> </span><span style=3D=
"color: #066;" class=3D"styled-by-prettify">2.0f</span><span style=3D"color=
: #660;" class=3D"styled-by-prettify">);</span><span style=3D"color: #000;"=
 class=3D"styled-by-prettify"> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 </=
span><span style=3D"color: #800;" class=3D"styled-by-prettify">// Compiler =
inlines: float b =3D g_x * g_x;</span><span style=3D"color: #000;" class=3D=
"styled-by-prettify"><br>=C2=A0 =C2=A0 </span><span style=3D"color: #008;" =
class=3D"styled-by-prettify">float</span><span style=3D"color: #000;" class=
=3D"styled-by-prettify"> c </span><span style=3D"color: #660;" class=3D"sty=
led-by-prettify">=3D</span><span style=3D"color: #000;" class=3D"styled-by-=
prettify"> </span><span style=3D"color: #606;" class=3D"styled-by-prettify"=
>MyPow</span><span style=3D"color: #660;" class=3D"styled-by-prettify">(</s=
pan><span style=3D"color: #000;" class=3D"styled-by-prettify">g_x</span><sp=
an style=3D"color: #660;" class=3D"styled-by-prettify">,</span><span style=
=3D"color: #000;" class=3D"styled-by-prettify"> </span><span style=3D"color=
: #066;" class=3D"styled-by-prettify">1.0f</span><span style=3D"color: #660=
;" class=3D"styled-by-prettify">);</span><span style=3D"color: #000;" class=
=3D"styled-by-prettify"> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 </span><=
span style=3D"color: #800;" class=3D"styled-by-prettify">// Compiler inline=
s: float c =3D g_x;</span><span style=3D"color: #000;" class=3D"styled-by-p=
rettify"><br>=C2=A0 =C2=A0 </span><span style=3D"color: #008;" class=3D"sty=
led-by-prettify">float</span><span style=3D"color: #000;" class=3D"styled-b=
y-prettify"> d </span><span style=3D"color: #660;" class=3D"styled-by-prett=
ify">=3D</span><span style=3D"color: #000;" class=3D"styled-by-prettify"> <=
/span><span style=3D"color: #606;" class=3D"styled-by-prettify">MyPow</span=
><span style=3D"color: #660;" class=3D"styled-by-prettify">(</span><span st=
yle=3D"color: #000;" class=3D"styled-by-prettify">g_x</span><span style=3D"=
color: #660;" class=3D"styled-by-prettify">,</span><span style=3D"color: #0=
00;" class=3D"styled-by-prettify"> g_y</span><span style=3D"color: #660;" c=
lass=3D"styled-by-prettify">);</span><span style=3D"color: #000;" class=3D"=
styled-by-prettify"> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0</span=
><span style=3D"color: #800;" class=3D"styled-by-prettify">// Compiler inli=
nes: float d =3D powf(g_x, g_y);</span><span style=3D"color: #000;" class=
=3D"styled-by-prettify"><br><br><br>=C2=A0 =C2=A0 </span><span style=3D"col=
or: #008;" class=3D"styled-by-prettify">float</span><span style=3D"color: #=
000;" class=3D"styled-by-prettify"> y </span><span style=3D"color: #660;" c=
lass=3D"styled-by-prettify">=3D</span><span style=3D"color: #000;" class=3D=
"styled-by-prettify"> </span><span style=3D"color: #066;" class=3D"styled-b=
y-prettify">0.f</span><span style=3D"color: #660;" class=3D"styled-by-prett=
ify">;</span><span style=3D"color: #000;" class=3D"styled-by-prettify"><br>=
=C2=A0 =C2=A0 </span><span style=3D"color: #008;" class=3D"styled-by-pretti=
fy">float</span><span style=3D"color: #000;" class=3D"styled-by-prettify"> =
e </span><span style=3D"color: #660;" class=3D"styled-by-prettify">=3D</spa=
n><span style=3D"color: #000;" class=3D"styled-by-prettify"> </span><span s=
tyle=3D"color: #606;" class=3D"styled-by-prettify">MyPow</span><span style=
=3D"color: #660;" class=3D"styled-by-prettify">(</span><span style=3D"color=
: #000;" class=3D"styled-by-prettify">g_x</span><span style=3D"color: #660;=
" class=3D"styled-by-prettify">,</span><span style=3D"color: #000;" class=
=3D"styled-by-prettify"> y</span><span style=3D"color: #660;" class=3D"styl=
ed-by-prettify">);</span><span style=3D"color: #000;" class=3D"styled-by-pr=
ettify"> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0</span><spa=
n style=3D"color: #800;" class=3D"styled-by-prettify">// Optimizing</span><=
span style=3D"color: #800;" class=3D"styled-by-prettify"> compiler SHOULD i=
nline: float e =3D 1.0f; Because y is known at compile time.</span><span st=
yle=3D"color: #000;" class=3D"styled-by-prettify"><br><br><br>=C2=A0 =C2=A0=
 </span><span style=3D"color: #008;" class=3D"styled-by-prettify">return</s=
pan><span style=3D"color: #000;" class=3D"styled-by-prettify"> </span><span=
 style=3D"color: #066;" class=3D"styled-by-prettify">0</span><span style=3D=
"color: #660;" class=3D"styled-by-prettify">;</span><span style=3D"color: #=
000;" class=3D"styled-by-prettify"><br></span><span style=3D"color: #660;" =
class=3D"styled-by-prettify">}</span></div></code></div><div><br></div></di=
v><div><br><div>This of course makes the assumption that the compiler is ob=
ligated to skip compilation of code that fails the constexpr if conditional=
 where it would instead compile the code in the else blocks, and vice versa=
 where the if constexpr passes. It&#39;s also worth mentioning that there s=
hould be no guarantee that just because a variable is assigned to a literal=
 and then immediately queried for std::is_constant_evaluated that it will r=
eturn true. It&#39;s up to the compiler to respect this case only when the =
variable is optimized in a way to be treated as such. For example, it may r=
eturn false in a non-optimized build, but true in an optimized build where =
inline expansion is guaranteed.</div><div><br></div><div>As far as the prec=
eding example goes, yes, I went straight to the float use case, which is no=
rmally non-integral, but I wanted to also demonstrate that this works aroun=
d the issue where floats cannot be template arguments in a more elegant and=
 uniformly obvious way where a function author can optimize for specific ca=
ses and combinations of literal values.</div></div><div><br></div></div>

<p></p>

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