http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50749
Bug #: 50749 Summary: SH Target: Post-increment addressing used only for first memory access Classification: Unclassified Product: gcc Version: 4.7.0 Status: UNCONFIRMED Severity: enhancement Priority: P3 Component: target AssignedTo: unassig...@gcc.gnu.org ReportedBy: oleg.e...@t-online.de CC: kkoj...@gcc.gnu.org Target: sh*-*-* Post-increment addressing is generated only for the first memory access. Any subsequent memory access does not use post-increment addressing. The following two functions are reduced examples and result in the same code being generated. The problem exists with any number of memory accesses > 1 and at any optimization level. int test_0 (char* p, int c) { int r = 0; r += *p++; r += *p++; r += *p++; return r; } int test_1 (char* p, int c) { int r = 0; r += p[0]; r += p[1]; r += p[2]; return r; } compiled with -fno-ivopts -Os -m4-single -ml ... mov r4,r1 mov.b @r1+,r0 add #2,r4 mov.b @r1,r1 add r1,r0 mov.b @r4,r1 rts add r1,r0 This could be done better ... mov.b @r4+,r0 mov.b @r4+,r1 add r1,r0 mov.b @r4+,r1 rts add r1,r0 Another example with a loop: int test_func_1 (char* p, int c) { int r = 0; do { r += *p++; r += *p++; } while (--c); return r; } compiled with -fno-ivopts -Os -m4-single -ml ... mov #0,r0 .L5: mov r4,r1 mov.b @r1+,r2 dt r5 mov.b @r1,r1 add r2,r0 add #2,r4 bf/s .L5 add r1,r0 rts nop would be better as: mov #0, r0 .L5: mov.b @r4+, r1 dt r5 mov.b @r4+, r2 add r1, r0 bf/s .L5 add r2, r0 rts nop Using built-in specs. COLLECT_GCC=sh-elf-gcc COLLECT_LTO_WRAPPER=/usr/local/libexec/gcc/sh-elf/4.7.0/lto-wrapper Target: sh-elf Configured with: ../gcc-trunk/configure --target=sh-elf --prefix=/usr/local --enable-languages=c,c++ --enable-multilib --disable-libssp --disable-nls --disable-werror --enable-lto --with-newlib --with-gnu-as --with-gnu-ld --with-system-zlib Thread model: single gcc version 4.7.0 20111016 (experimental) (GCC)