https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89143
Bug ID: 89143 Summary: [9 Regression] comparison of abs(i) against excessive constant less than UXXX_MAX no longer folded Product: gcc Version: 9.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: tree-optimization Assignee: unassigned at gcc dot gnu.org Reporter: msebor at gcc dot gnu.org Target Milestone: --- While looking into bug 89127 I noticed that while GCC 8 and prior fold the comparison to false in the if controlling expression below due to the limited range of i's type, GCC 9 no longer performs this folding unless the constant is UCHAR_MAX and greater. Same for short and SHRT_MAX + 1. $ cat u.c && gcc -S -O2 -Wall -Wextra -Wtype-limits -fdump-tree-optimized=/dev/stdout u.c void f (signed char i) { if (__builtin_abs (i) > 128) __builtin_abort (); } ;; Function f (f, funcdef_no=0, decl_uid=1906, cgraph_uid=1, symbol_order=0) f (signed char i) { unsigned char _1; <bb 2> [local count: 1073741824]: _1 = ABSU_EXPR <i_2(D)>; if (_1 > 128) goto <bb 3>; [0.00%] else goto <bb 4>; [100.00%] <bb 3> [count: 0]: __builtin_abort (); <bb 4> [local count: 1073741824]: return; }