We compiled a program (A.c) by GCC-5.1.0 and GCC-6.0.0 with -O3 option. GCC-5.1.0 performed better optimization than GCC-6.0.0. (A.c) int main (void) { volatile int x1 = 1; volatile int x2 = 1; int x3 = 2; int t = 1; t = 3<=(x2|1|x3|x1-1U); if (t == 1) {} else { __builtin_abort(); } return 0; } +--------------------------------------+--------------------------------------+ | gcc-5.1.0.s (gcc-5.1.0 A.c -O3 -S) | gcc-6.0.0.s (gcc-6.0.0 A.c -O3 -S) | +--------------------------------------+--------------------------------------+ |main: |main: | |.LFB0: |.LFB0: | | .cfi_startproc | .cfi_startproc | | movl $1, -8(%rsp) | subq $24, %rsp | | movl $1, -4(%rsp) | .cfi_def_cfa_offset 32 | | movl -4(%rsp), %eax | movl $1, 8(%rsp) | | movl -8(%rsp), %eax | movl $1, 12(%rsp) | | | movl 12(%rsp), %eax | | | movl 8(%rsp), %edx | | | orl $3, %eax | | | movl %eax, %ecx | | | leal -1(%rdx), %eax | | | orl %ecx, %eax | | | cmpl $2, %eax | | | jbe .L5 | | xorl %eax, %eax | xorl %eax, %eax | | | addq $24, %rsp | | | .cfi_remember_state | | | .cfi_def_cfa_offset 8 | | ret | ret | | |.L5: | | | .cfi_restore_state | | | call abort | | .cfi_endproc | .cfi_endproc | |.LFE0: |.LFE0: | | .size main, .-main | .size main, .-main | | .section .text.unlikely| .ident "GCC: (GNU) 6.0.0 ...| |.LCOLDE0: | | | .section .text.startup | | |.LHOTE0: | | | .ident "GCC: (Ubuntu 5.1.0...| | | .section .note.GNU-s...| .section .note.GNU-s...| +--------------------------------------+--------------------------------------+ Using built-in specs. COLLECT_GCC=gcc-5 COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/5/lto-wrapper Target: x86_64-linux-gnu Configured with: ../src/configure -v --with-pkgversion='Ubuntu 5.1.0-0ubuntu11~14.04.1' --with-bugurl=file:///usr/share/doc/gcc-5/README.Bugs --enable-languages=c,ada,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-5 --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=c++98 --enable-gnu-unique-object --disable-vtable-verify --enable-libmpx --enable-plugin --with-system-zlib --disable-browser-plugin --enable-java-awt=gtk --enable-gtk-cairo --with-java-home=/usr/lib/jvm/java-1.5.0-gcj-5-amd64/jre --enable-java-home --with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-5-amd64 --with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-5-amd64 --with-arch-directory=amd64 --with-ecj-jar=/usr/share/java/eclipse-ecj.jar --enable-objc-gc --enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu Thread model: posix gcc version 5.1.0 (Ubuntu 5.1.0-0ubuntu11~14.04.1) Using built-in specs. COLLECT_GCC=gcc-6.0 COLLECT_LTO_WRAPPER=/home/iwatsuji/opt/gcc-6.0/libexec/gcc/x86_64-pc-linux-gnu/6.0.0/lto-wrapper Target: x86_64-pc-linux-gnu Configured with: ../gcc/configure --prefix=/home/iwatsuji/opt/gcc-6.0 --program-suffix=-6.0 --disable-multilib --enable-languages=c Thread model: posix gcc version 6.0.0 20151014 (experimental) (GCC)
t = 3<=(x2|1|x3|x1-1U); Doing the non-volatile sub: t = 3 <= (x2 | 1 | 2 | (x1 - 1u)) ... t = 3 <= (x2 | 3 | (x1 - 1u)) or: t = 3 <= 3 | x2 | (x1 - 1u) Which is: t = true, x1, x2. Only if re-association happens with casts thrown in too which might be the case of the regression.
Started with r222085.
Mine.
Fixed.
Author: rguenth Date: Wed Oct 21 07:56:54 2015 New Revision: 229117 URL: https://gcc.gnu.org/viewcvs?rev=229117&root=gcc&view=rev Log: 2015-10-21 Richard Biener <rguenther@suse.de> PR tree-optimization/68026 * tree-ssa-ccp.c (get_value_for_expr): Zero-extend mask for unsigned VARYING values. * gcc.dg/tree-ssa/ssa-ccp-39.c: New testcase. Added: trunk/gcc/testsuite/gcc.dg/tree-ssa/ssa-ccp-39.c Modified: trunk/gcc/ChangeLog trunk/gcc/testsuite/ChangeLog trunk/gcc/tree-ssa-ccp.c