fanqifei wrote:
Is there anyone can help? I am curious about how the insv pattern can be used in the compiling process. Otherwise, I have to write inline assembly code. Thanks very much!
You don't state which compiler version you are using. I would suggest trying a GCC-4.5 snapshot. I know that some work has been recently done to make better use of INS.
If GCC-4.5 doesn't help, you could file a GCC bug report about this missed optimization.
David Daney
2009/12/16 fanqifei <fanqifei@xxxxxxxxx>:Hello, I am tring to compile a small c file using gcc4.1.2. The source code: struct test_foo { unsigned int a:18; unsigned int b:2; unsigned int c:12; }; struct test_foo x; unsigned int foo() { unsigned int a=x.b; x.b=2; return a; } the command: mipsel-linux-gcc -mips32r2 -O2 -c -Wall foo.c -o foo.o The corresponding disassembly code: foo.o: file format elf32-tradlittlemips Disassembly of section .text: 00000000 <foo>: 0: 3c1c0000 lui gp,0x0 4: 279c0000 addiu gp,gp,0 8: 0399e021 addu gp,gp,t9 c: 8f850000 lw a1,0(gp) 10: 3c03fff3 lui v1,0xfff3 14: 3463ffff ori v1,v1,0xffff 18: 8ca20000 lw v0,0(a1) 1c: 3c040008 lui a0,0x8 20: 00431824 and v1,v0,v1 24: 00641825 or v1,v1,a0 28: 7c420c80 ext v0,v0,0x12,0x2 2c: 03e00008 jr ra 30: aca30000 sw v1,0(a1) The statement x.b=2 can be simply translated to lb and ins instructions( ins is in mips32r2). I wonder how ins instrution can be produced. More specifically, how can gcc generates the insv pattern in RTL? Is it related to the coding style -- using bit filed or logical operations(shift, and ...)? Thanks. Qifei
