Add Stephen's llvm-cbuilder examples.

README_LLVM_CBUILDER.md

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+LLVM CBuilder
+=============
+
+A few short examples:
+(TODO: add more later)
+
+```python
+from llvm.core import *
+from llvm_cbuilder import *
+import llvm_cbuilder.shortnames as C
+```
+
+```python
+class Square(CDefinition):
+    _name_ = 'square'
+    _retty_ = C.double
+    _argtys_ = [ ('x', C.double) ]
+
+    def body(self, x):
+        y = x * x
+        self.ret(y)
+```
+
+```python
+m = Module.new('my_module')
+llvm_square = Square()(m)
+print(m)
+```
+
+```
+; ModuleID = 'my_module'
+
+define double @square(double %x) {
+decl:
+  %0 = fmul double %x, %x
+  ret double %0
+}
+```
+
+
+```python
+class IsPrime(CDefinition):
+    _name_ = 'isprime'
+    _retty_ = C.int
+    _argtys_ = [('x', C.int)]
+
+    def body(self, x):
+        false = zero = self.constant(C.int, 0)
+        true = one = self.constant(C.int, 1)
+
+        two = self.constant(C.int, 2)
+
+        with self.ifelse( x <= two ) as ifelse:
+            with ifelse.then():
+                self.ret(true)
+
+        with self.ifelse( (x % two) == zero ) as ifelse:
+            with ifelse.then():
+                self.ret(false)
+
+        idx = self.var(C.int, 3, name='idx')
+
+        with self.loop() as loop:
+            with loop.condition() as setcond:
+                setcond( idx < x )
+
+            with loop.body():
+                with self.ifelse( (x % idx ) == zero ) as ifelse:
+                    with ifelse.then():
+                        self.ret(false)
+                idx += two
+
+        self.ret(true)
+```
+
+
+
+```
+define i32 @isprime(i32 %x) {
+decl:
+  %0 = icmp sle i32 %x, 2
+  br i1 %0, label %if.then, label %if.end
+
+if.then:                                          ; preds = %loop.body, %loop.cond, %if.end, %decl
+  %merge = phi i32 [ 1, %decl ], [ 0, %if.end ], [ 1, %loop.cond ], [ 0, %loop.body ]
+  ret i32 %merge
+
+if.end:                                           ; preds = %decl
+  %1 = srem i32 %x, 2
+  %2 = icmp eq i32 %1, 0
+  br i1 %2, label %if.then, label %if.end4
+
+if.end4:                                          ; preds = %if.end
+  br label %loop.cond
+
+loop.cond:                                        ; preds = %if.end7, %if.end4
+  %idx.0 = phi i32 [ 3, %if.end4 ], [ %6, %if.end7 ]
+  %3 = icmp slt i32 %idx.0, %x
+  br i1 %3, label %loop.body, label %if.then
+
+loop.body:                                        ; preds = %loop.cond
+  %4 = srem i32 %x, %idx.0
+  %5 = icmp eq i32 %4, 0
+  br i1 %5, label %if.then, label %if.end7
+
+if.end7:                                          ; preds = %loop.body
+  %6 = add i32 %idx.0, 2
+  br label %loop.cond
+}
+
+; ModuleID = 'my_module'
+
+define i32 @isprime(i32 %x) {
+decl:
+  %0 = icmp sle i32 %x, 2
+  br i1 %0, label %if.then, label %if.end
+
+if.then:                                          ; preds = %loop.body, %loop.cond, %if.end, %decl
+  %merge = phi i32 [ 1, %decl ], [ 0, %if.end ], [ 1, %loop.cond ], [ 0, %loop.body ]
+  ret i32 %merge
+
+if.end:                                           ; preds = %decl
+  %1 = srem i32 %x, 2
+  %2 = icmp eq i32 %1, 0
+  br i1 %2, label %if.then, label %if.end4
+
+if.end4:                                          ; preds = %if.end
+  br label %loop.cond
+
+loop.cond:                                        ; preds = %if.end7, %if.end4
+  %idx.0 = phi i32 [ 3, %if.end4 ], [ %6, %if.end7 ]
+  %3 = icmp slt i32 %idx.0, %x
+  br i1 %3, label %loop.body, label %if.then
+
+loop.body:                                        ; preds = %loop.cond
+  %4 = srem i32 %x, %idx.0
+  %5 = icmp eq i32 %4, 0
+  br i1 %5, label %if.then, label %if.end7
+
+if.end7:                                          ; preds = %loop.body
+  %6 = add i32 %idx.0, 2
+  br label %loop.cond
+}
+```