ado@elsie.UUCP (Arthur David Olson) (09/12/85)
Index: src/lib/pcc/code.c Fix Description: The 4.?BSD C compiler and optimizer can fail to produce optimized code for expressions that appear just before a value-free "return". Repeat-By: Compile this source a la "cc -S -O": one(i, j, k) { i = j * k; dummy(); } two(i, j, k) { dummy(); i = j * k; } ...and note the differences in the code produced for the two functions. Fix: The fix involves changing two files. As usual, the trade secret status of the code involved precludes a clearer posting. The idea was suggested by umcp-cs!chris. Change the indicated line in "pcc/code.c": #ifdef OLDVERSION printf( " ret\n" ); #else if ((retstat & RETVAL) == 0) printf("\tret\t# return;\n"); else printf("\tret\n"); #endif ...and make this change to "c2/c21.c": #ifdef OLDVERSION if (p->subop==RET || p->subop==RSB) {uses[0]=p; regs[0][0]= -1; break;} #else if (p->subop == RET || p->subop == RSB) { if (p->code == 0 || !equstr(p->code, "# return;")) uses[0] = p; regs[0][0] = -1; break; } #endif Of course I'm no wizard, so you may want to await the verdict of other readers of net.bugs.4bsd before making this change. -- C is a Mel Blanc/Jack Benny trademark. -- UUCP: ..decvax!seismo!elsie!ado ARPA: elsie!ado@seismo.ARPA DEC, VAX and Elsie are Digital Equipment and Borden trademarks
mjs@sfmag.UUCP (M.J.Shannon) (09/15/85)
> Index: src/lib/pcc/code.c Fix > > Description: > The 4.?BSD C compiler and optimizer can fail to produce optimized > code for expressions that appear just before a value-free "return". > > Fix: > The fix involves changing two files. As usual, the trade secret status > of the code involved precludes a clearer posting. The idea was > suggested by umcp-cs!chris. > > Change the indicated line in "pcc/code.c": > > #ifdef OLDVERSION > printf( " ret\n" ); > #else > if ((retstat & RETVAL) == 0) > printf("\tret\t# return;\n"); > else printf("\tret\n"); > #endif > > ...and make this change to "c2/c21.c": > > #ifdef OLDVERSION > if (p->subop==RET || p->subop==RSB) {uses[0]=p; regs[0][0]= -1; break;} > #else > if (p->subop == RET || p->subop == RSB) { > if (p->code == 0 || > !equstr(p->code, "# return;")) > uses[0] = p; > regs[0][0] = -1; > break; > } > #endif > > UUCP: ..decvax!seismo!elsie!ado ARPA: elsie!ado@seismo.ARPA > DEC, VAX and Elsie are Digital Equipment and Borden trademarks You also have to deal with the case that the function may be returning a double (which takes r0 & r1). Once upon a time (in a galaxy far, far away) I fixed this problem for the AT&T VAX compiler/optimizer. I have no idea of the current status of those fixes. Oh, the return value may also be a structure, but I don't recal the maximum size that will be returned in registers. -- Marty Shannon UUCP: ihnp4!attunix!mjs Phone: +1 (201) 522 6063 Disclaimer: I speak for no one.