int x; void __attribute__((noinline)) foo (void) { x = -x; } void __attribute__((const,noinline)) bar (void) { }
int __attribute__((noinline)) test (int c) { int tmp = x; (c ? foo : bar) (); return tmp + x; } extern void abort (void); int main() { x = 1; if (test (1) != 0) abort (); return 0; } creates wrong code because the side-effect of the call to foo() is not accounted for. Since the merge of tree-ssa already gimplification removes the function call. Thus, the above fails with -O0. If you modify the testcase to use the return-value, you see that wrong alias information is created because we appearantly use the const attribute for the indirect call. int x; int __attribute__((noinline)) foo (void) { x = -x; return 0; } int __attribute__((const,noinline)) bar (void) { return 0; } int __attribute__((noinline)) test (int c) { int tmp = x; int res = (c ? foo : bar) (); return tmp + x + res; } extern void abort (void); int main() { x = 1; if (test (1) != 0) abort (); return 0; } alias produced is: test (c) { int res; int tmp; int D.1207; int x.3; int D.1205; int (*<T240>) (void) iftmp.2; <bb 2>: # VUSE <x_11(D)> tmp_2 = x; if (c_3(D) != 0) goto <bb 4>; else goto <bb 3>; <bb 3>: <bb 4>: # iftmp.2_1 = PHI <foo(2), bar(3)> res_6 = iftmp.2_1 (); # VUSE <x_11(D)> x.3_7 = x; D.1207_8 = tmp_2 + x.3_7; D.1205_9 = D.1207_8 + res_6; return D.1205_9; } and we happily CSE the load from x. This testcase requires -O to fail. -- Summary: [4.1/4.2/4.3 Regression] Wrong code with conditional function invocation Product: gcc Version: 4.3.0 Status: UNCONFIRMED Keywords: wrong-code Severity: normal Priority: P3 Component: middle-end AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: rguenth at gcc dot gnu dot org http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34768