http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49263
Summary: SH Target: underutilized "TST #imm, R0" instruction Product: gcc Version: 4.6.1 Status: UNCONFIRMED Severity: enhancement Priority: P3 Component: target AssignedTo: unassig...@gcc.gnu.org ReportedBy: oleg.e...@t-online.de Created attachment 24411 --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24411 test for various integer types and constant values 0...255 The "TST #imm, R0" instruction is a bit underutilized on SH targets. For some bit patterns of the immediate constant it tries to extract the bits in question by various means and test the result against zero/non-zero and misses the straight forward instruction. In particular: * one single bit * n contiguous bits starting at bit 0 When testing a byte against 0x80 it uses "CMP/PZ", which is as good as a "TST" instruction (in terms of costs), so this is OK. I've spotted this in version around 4.4. It still happens with 4.6 and the following config: Using built-in specs. COLLECT_GCC=sh-elf-gcc COLLECT_LTO_WRAPPER=/usr/local/libexec/gcc/sh-elf/4.6.1/lto-wrapper Target: sh-elf Configured with: ../gcc-4.6-20110527/configure --target=sh-elf --prefix=/usr/local --enable-languages=c,c++ --enable-multilib --disable-libssp --without-headers --disable-nls --disable-werror --enable-lto --with-newlib --with-gnu-as --with-gnu-ld --with-system-zlib Thread model: single gcc version 4.6.1 20110527 (prerelease) (GCC)