On Mon, Feb 12, 2018 at 03:59:05PM +0000, Segher Boessenkool wrote: > If there is a LOG_LINK between two insns, this means those two insns > can be combined, as far as dataflow is concerned. There never should > be a LOG_LINK between two unrelated insns. If there is one, combine > will try to combine the insns without doing all the needed checks if > the earlier destination is used before the later insn, etc. > > Unfortunately we do not update the LOG_LINKs correctly in some cases. > This patch fixes at least some of those cases. > > This fixes the PR's testcase on aarch64. Also tested on 30+ cross > compiler, and on powerpc64-linux {-m32,-m64}. Will test on x86_64 > as well before committing.
Will you check in the testcase too? My preference would be something like following, so that it can be torture-tested on all targets. --- gcc/testsuite/gcc.c-torture/execute/pr84169.c 2018-01-12 10:39:42.940283691 +0100 +++ gcc/testsuite/gcc.c-torture/execute/pr84169.c 2018-02-12 17:11:18.970878978 +0100 @@ -0,0 +1,25 @@ +/* PR rtl-optimization/84169 */ + +#ifdef __SIZEOF_INT128__ +typedef unsigned __int128 T; +#else +typedef unsigned long long T; +#endif + +T b; + +static __attribute__ ((noipa)) T +foo (T c, T d, T e, T f, T g, T h) +{ + __builtin_mul_overflow ((unsigned char) h, -16, &h); + return b + h; +} + +int +main () +{ + T x = foo (0, 0, 0, 0, 0, 4); + if (x != -64) + __builtin_abort (); + return 0; +} Jakub