glsl: Recognize open-coded pow(x, y).
glsl: Recognize open-coded pow(x, y).

pow(x, y) is equivalent to exp(log(x) * y).

instructions in affected programs:     578 -> 458 (-20.76%)

Reviewed-by: Kenneth Graunke <bd2562f754ec92342f93f61c25d731e290a2ffa8@whitecape.org>

dellis1972/glsl-optimizer,zz85/glsl-optimizer,zeux/glsl-optimizer,mcanthony/glsl-optimizer,bkaradzic/glsl-optimizer,benaadams/glsl-optimizer,djreep81/glsl-optimizer,zeux/glsl-optimizer,tokyovigilante/glsl-optimizer,jbarczak/glsl-optimizer,metora/MesaGLSLCompiler,bkaradzic/glsl-optimizer,jbarczak/glsl-optimizer,jbarczak/glsl-optimizer,zz85/glsl-optimizer,wolf96/glsl-optimizer,jbarczak/glsl-optimizer,metora/MesaGLSLCompiler,wolf96/glsl-optimizer,benaadams/glsl-optimizer,tokyovigilante/glsl-optimizer,benaadams/glsl-optimizer,dellis1972/glsl-optimizer,zeux/glsl-optimizer,mcanthony/glsl-optimizer,jbarczak/glsl-optimizer,mcanthony/glsl-optimizer,wolf96/glsl-optimizer,zz85/glsl-optimizer,bkaradzic/glsl-optimizer,djreep81/glsl-optimizer,bkaradzic/glsl-optimizer,benaadams/glsl-optimizer,djreep81/glsl-optimizer,tokyovigilante/glsl-optimizer,mcanthony/glsl-optimizer,wolf96/glsl-optimizer,zz85/glsl-optimizer,zeux/glsl-optimizer,djreep81/glsl-optimizer,dellis1972/glsl-optimizer,benaadams/glsl-optimizer,tokyovigilante/glsl-optimizer,zeux/glsl-optimizer,bkaradzic/glsl-optimizer,djreep81/glsl-optimizer,benaadams/glsl-optimizer,metora/MesaGLSLCompiler,dellis1972/glsl-optimizer,mcanthony/glsl-optimizer,wolf96/glsl-optimizer,dellis1972/glsl-optimizer,zz85/glsl-optimizer,tokyovigilante/glsl-optimizer,zz85/glsl-optimizer