"redriver jiang" <[EMAIL PROTECTED]> writes: > I am Jiang Hongjiang and recently I am porting the GCC backend > to a DSP, and get puzzled about the "decrement_and_branch_until_zero" > pattern.By Reading the GCC source, I find that this pattern is used in > loop optimization, and it's used under the condition of defining the > "doloop_end" pattern. Inspired by the c4x machine description file( > c4x.md), I defined the "doloop_end" pattern using "define_expand", and > generate the "decrement_and_branch_until_zero" insn in the preparation > statements. Right now the GCC can generate the > "decrement_and_branch_until_zero" insns and its related assemble > insn(in my platform it is "DJNZ Rn,lable"), but I find that the GCC > remains other insns(the cmp insns and other) unchanged. How do you > delete the "CMP" insn and other insn in the loop while using the > "decrement_and_branch_until_zero" pattern? The accessory demonstrates > a example.
Normally the compare instruction is removed later because it is unused: it is nonvolatile and nothing uses the result. You must determine why the compiler thinks that the compare instruction is still used. Ian
