274 

   274 }

   275 }

   275 

   276 

   277 

   278 

   279 

   280 /*

   281 LLVM notes

   282 

   283 Registers are places for data inside the CPU.

   284 + up to 10 times faster access than to main memory 

   285 - expensive; typically just 32 of them in a 32-bit CPU

   286 

   287 High-level view of x86

   288 • Not a stack machine; no direct correspondence to operand stacks

   289 • Arithmetics, etc. is done with values in registers

   290 

   291 • Started as academic project at University of Illinois in 2002

   292 • Now a large open source project with many contributors and a growing user base

   293 

   294 Single Static Assignment (SSA) form

   295 • Only one assignment in the program text to each variable

   296 • But dynamically, this assignment can be executed many times

   297 • Many stores to a memory location are allowed

   298 • Also, Φ (phi) instructions can be used, in the beginning of a basic block

   299 • Value is one of the arguments, depending on from which block control came to this block

   300 • Register allocation tries to keep these variables in same real register

   301 

   302 Why SSA form?

   303 Many code optimizations can be done more efficiently

   304 

   305 Function definition form

   306  define t @name(t1 x1, t2 x2, ..., tn xn) {

   307  l1: block1

   308  l2: block2

   309  ... 

   310  lm : blockm

   311  }

   312 

   313 

   314 

   315 

   316 */