281 /*

   282 LLVM notes

   283 

   284 Registers are places for data inside the CPU.

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

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

   287 

   288 High-level view of x86

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

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

   291 

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

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

   294 

   295 Single Static Assignment (SSA) form

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

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

   298 • Many stores to a memory location are allowed

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

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

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

   302 

   303 Why SSA form?

   304 Many code optimizations can be done more efficiently

   305 

   306 Function definition form

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

   308  l1: block1

   309  l2: block2

   310  ... 

   311  lm : blockm

   312  }

   313 

   314 

   315 

   316 

   317 */