Compiler - conditional/loop code generation

Code Generation for Conditional Judgment Statements

st1
if(r1<r2)
    st2
else 
    st3
st4

                st1

BB1 com_LT r1,r2 → r3

               cbr r3 → L1,L2

        L1 : st2

BB2 jumpI L3

BB3 L2 : st3

BB4 L3 : st4

The com_LT here is less than if r1 is smaller than r2, return true to r3
cbr is a condition branch, if r3 is true, go to L1, otherwise go to L2

The basic block represented by BB is a basic block when encountering a branch or jump or a new label.

Control Flow Graph（CFG） 

Dividing the code into these basic blocks will make the logic clearer and the optimization work easier.
After obtaining the AST, the compiler will build such a CFG as a part of the middle expression. There are some linear assembly instructions in each baisc block.

Cyclic code generation

st1
while(r1==r2)
    st2
st3

The first way of writing: 

                st1

BB1        com_EQ r1,r2 → r3

               cbr r3 → L1,L2

               L1 : st2

BB3        com_EQ r1,r2 → r3

               cbr r3 → L1,L2

BB3 L2 : st3

CFG：
 

 second way of writing

BB1 st1

BB2        L0 : com_EQ r1,r2 → r3

               cbr r3 → L1,L2

BB3        L1 : st2

               jumpI L0

BB4        L2 : st3

Because L0 has 4 basic block
CFGs at this time:

boolean type

a > b && c==d || e<=f

loadAI rarp,@a → r1

loadAI rarp,@b → r2

comp_GT r1,r2 → r3

loadAI rarp,@c → r4

loadAI rarp,@d → r5

cmp_EQ r4,r5 → r6

and r3,r6 → r7

loadAI rarp,@e → r8

loadAI rarp,@f → r9

cmp_LE r8, r9 → r10

or r7,r10 → r11

 Nested loops:

st1;
while(r1>r2)
{
    st2;
    while(r3<=r4)
    {
        st3;
    }
    st4;
}
st5;

 L1_B : Loop body
 L1_O : Loop out
 L1_C : Loop condition

            st1

L1_C : cmp_GT r1,r2 → r5

            cbr r5 → L1_B,L1_O

L1_B   st2

L1_C   cmp_LE r3,r4 → r6

            cbr r6 → L2_B,L2_O

L2_B : st3

            jumpI L2_C

L2_O : st4

            jumpI L1_C

L1_O : st5