| Summary: | while and (type *&)variable++ causes never ending loop | ||
|---|---|---|---|
| Product: | gcc | Reporter: | kalas <kalas> |
| Component: | c++ | Assignee: | Not yet assigned to anyone <unassigned> |
| Status: | RESOLVED DUPLICATE | ||
| Severity: | normal | CC: | adruab, Andreas.Glowatz, andreg, bobm75, boris, c.pop, cdfrey, charles, christophe.guillon, cxl, czang, d.bonekaemper, danfuzz, davids, davmac, devin, djk, dmeggy, duraid, evgeny, ezharkov, fabdouze, fm, gcc-bugs, gcc, ghouston, gino, gopalv82, grigory_zagorodnev, hayim, horst.lehser, hurbain, ja2morri, jason.elbaum, jfran, jochang, larschri, lindsayd, linuxadmin, lucho, l_heldt, micis, mike, mor_gopal, noaml, pgonzalez, pierre.chatelier, pjh, rarob, renzo, rick.ju, spelis, steffen.zimmermann, steger, strasbur, sumii, thomas.anders, warp, zengpan, zybi |
| Priority: | P3 | ||
| Version: | 4.0.2 | ||
| Target Milestone: | --- | ||
| Host: | cygwin | Target: | arm-elf |
| Build: | Known to work: | ||
| Known to fail: | Last reconfirmed: | ||
This is not a valid testcase, or even expression. I guess it's invalid anyway because of operator precedence. It's a valid C++ fragment. However, this code accesses "ptr", which is of type void*, via an lvalue of type U16*. This is undefined behavior, so there is no gcc bug here. Oh, this is just an aliasing issue. Reopening... |
Following code is not compiled correctly and causes never ending loop. GCC 4.0.2 from GNUARM.org distribution was used. typedef unsigned short U16; void * ptr = buffer; void * end = (U16 *)buffer + num; while (ptr != end) { *((U16 *&)ptr)++ = c; } dissasebly with intermixed source code: void * ptr = buffer; void * end = (U16 *)buffer + num; 924: e2812a02 add r2, r1, #8192 ; 0x2000 while (ptr != end) 928: e1520001 cmp r2, r1 92c: e50b1038 str r1, [fp, #-56] 930: 0a000250 beq 948 <_ZN7MvbcLSA8InitChipEhh+0x228> 934: e3a00000 mov r0, #0 ; 0x0 938: e1a03001 mov r3, r1 { *((U16 *&)ptr)++ = c; 93c: e0c300b2 strh r0, [r3], #2 940: 1a00024d bne 93c <_ZN7MvbcLSA8InitChipEhh+0x21c> 944: e50b3038 str r3, [fp, #-56] } arm-elf-gcc --ver Using built-in specs. Target: arm-elf Configured with: ../gcc-4.0.2/configure --target=arm-elf --prefix=/g/gnuarm-4.0.2 --enable-interwork --enable-multilib --with-newlib --with-headers=../newlib-1.14.0/newlib/libc/include --enable-languages=c,c++ Thread model: single gcc version 4.0.2