https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110867
Stefan Schulze Frielinghaus <stefansf at linux dot ibm.com> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |stefansf at linux dot ibm.com --- Comment #1 from Stefan Schulze Frielinghaus <stefansf at linux dot ibm.com> --- The optimization introduced by r14-2879-g7cdd0860949c6c hits during combination of insn (insn 31 3 32 2 (set (reg:SI 118 [ _1 ]) (mem:SI (reg/v/f:SI 115 [ a ]) [1 *a_4(D)+0 S4 A64])) "t.c":15:7 758 {*arm_movsi_vfp} (nil)) and (insn 9 32 10 2 (set (reg:CC 100 cc) (compare:CC (reg:SI 118 [ _1 ]) (const_int -2147483648 [0xffffffff80000000]))) "t.c":15:6 272 {*arm_cmpsi_insn} (nil)) The idea of r14-2879-g7cdd0860949c6c is to get rid of large constants while performing an unsigned comparison. In this case it looks like a 32-bit constant is sign-extended into a 64-bit constant and then a 32-bit comparison is done. While writing the optimization I always assumed that the constant does fit into int_mode which is apparently not the case here. Thus one possible solution would be to simply bail out in those cases: diff --git a/gcc/combine.cc b/gcc/combine.cc index 0d99fa541c5..e46d202d0a7 100644 --- a/gcc/combine.cc +++ b/gcc/combine.cc @@ -11998,11 +11998,15 @@ simplify_compare_const (enum rtx_code code, machine_mode mode, x0 >= 0x40. */ if ((code == LEU || code == LTU || code == GEU || code == GTU) && is_a <scalar_int_mode> (GET_MODE (op0), &int_mode) + && HWI_COMPUTABLE_MODE_P (int_mode) && MEM_P (op0) && !MEM_VOLATILE_P (op0) /* The optimization makes only sense for constants which are big enough so that we have a chance to chop off something at all. */ && (unsigned HOST_WIDE_INT) const_op > 0xff + /* Bail out, if the constant does not fit into INT_MODE. */ + && (unsigned HOST_WIDE_INT) const_op + < ((HOST_WIDE_INT_1U << (GET_MODE_PRECISION (int_mode) - 1) << 1) - 1) /* Ensure that we do not overflow during normalization. */ && (code != GTU || (unsigned HOST_WIDE_INT) const_op < HOST_WIDE_INT_M1U)) { Does this resolve the problem for you?