Compilers: Principles and Practice by Pearson

Project: Compiler for a MiniC 369

The corresponding raw assembly code generator function – efgt() – looks like

efgt(){

emit(" fcomip %%st(1)\n",0); // want "st(1) > st(0)?"

emit(" setc %%al\n",0); // i.e. TOS < st(1)

emit(" andl $1, %%eax\n",0); // 1st 2nd

emit(" fstp FPacc\n",0);

}

The floating point compares the instruction sets two flags C and Z. We set al to 1 if the C is set, i.e.

TOS is less than the second operand. Remember we want to check if al is 0 or 1, which is achieved

by the andl instruction. This will set up the flags again for a subsequent JZ instruction.

Other comparisons are implemented in similar ways.

12.8.4