http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52049
Bug #: 52049 Summary: SH Target: Inefficient constant address 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*-*-* static volatile int* const g_0 = (volatile int*)0x1240; static volatile int* const g_1 = (volatile int*)0x1244; static volatile int* const g_2 = (volatile int*)0x1248; static volatile int* const g_3 = (volatile int*)0x124C; int test_24 (void) { return *g_0 + *g_1 + *g_2 + *g_3; } Compiled with -O1: mov.w .L31,r1 mov.l @r1+,r0 mov.l @r1+,r3 mov.l @r1+,r2 mov.l @r1,r1 add r3,r0 add r2,r0 rts add r1,r0 .align 1 .L31: .short 4672 Compiled with -O2, -Os, -O3: mov.w .L31,r1 mov.l @r1,r0 mov.l @(4,r1),r3 mov.l @(8,r1),r2 add #12,r1 ! why not mov.l @(12,r1),r1 ?? mov.l @r1,r1 add r3,r0 add r2,r0 rts add r1,r0 .align 1 .L31: .short 4672 This happens always for the last memory access, if the number of contiguous accesses is > 2. When using non-volatile variables: static int* const h_0 = (int*)0x1240; static int* const h_1 = (int*)0x1244; static int* const h_2 = (int*)0x1248; static int* const h_3 = (int*)0x124C; int test_25 (void) { return *h_0 + *h_1 + *h_2 + *h_3; } Compiled with -O1,-O2,-Os,-O3: mov.w .L33,r1 mov.l @r1+,r0 mov.l @r1,r1 add r1,r0 mov.w .L34,r1 mov.l @r1,r1 add r1,r0 mov.w .L35,r1 mov.l @r1,r1 rts add r1,r0 .align 1 .L33: .short 4672 .L34: .short 4680 .L35: .short 4684 Better: mov.w .L31,r1 mov.l @r1+,r0 mov.l @r1+,r3 mov.l @r1+,r2 add r3,r0 mov.l @r1,r1 add r2,r0 rts add r1,r0 .align 1 .L31: .short 4672 I'm not sure whether this is actually a problem of the SH back-end or of some middle-end passes. It happens for all sub-targets and regardless of the endianess. 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 20120129 (experimental) (GCC)