https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103658
Bug ID: 103658 Summary: missing -Wanalyzer-use-of-uninitialized-value at -O1 and below for an array access Product: gcc Version: 12.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: analyzer Assignee: dmalcolm at gcc dot gnu.org Reporter: msebor at gcc dot gnu.org Target Milestone: --- I came across this while comparing the middle end -Wuninitialized with -Wanalyzer-use-of-uninitialized-value. They both trigger at -O2. At -O1, only -Wuninitialized triggers, even though the IL looks the same between the two levels (as far as I can tell). $ cat z.c && gcc -O1 -S -Wall -fdump-tree-uninit=/dev/stdout -fanalyzer z.c int f (int i, int j) { int a[3]; a[0] = 1; a[1] = 2; if (i < 1) i = 1; if (j < 1) j = 1; return a[i + j]; } ;; Function f (f, funcdef_no=0, decl_uid=1979, cgraph_uid=1, symbol_order=0) z.c: In function ‘f’: z.c:9:11: warning: ‘a’ is used uninitialized [-Wuninitialized] 9 | return a[i + j]; | ~^~~~~~~ z.c:3:7: note: ‘a’ declared here 3 | int a[3]; | ^ int f (int i, int j) { int a[3]; int _1; int _6; int _8; int _9; <bb 2> [local count: 1073741824]: _8 = MAX_EXPR <i_5(D), 1>; _6 = MAX_EXPR <j_7(D), 1>; _1 = _6 + _8; _9 = a[_1]; a ={v} {CLOBBER}; return _9; }