From: Richard Biener Date: Thu, 22 Jul 2021 10:26:16 +0000 (+0200) Subject: tree-optimization/101573 - improve uninit warning at -O0 X-Git-Tag: basepoints/gcc-13~5788 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=66030d68a7edfc9504a50469598e0707b8f787ce;p=thirdparty%2Fgcc.git tree-optimization/101573 - improve uninit warning at -O0 We can improve uninit warnings from the early pass by looking at PHI arguments on fallthru edges that are uninitialized and have uses that are before a possible loop exit. This catches some cases earlier that we'd only warn in a more confusing way after early inlining as seen by testcase adjustments. It introduces FAIL: gcc.dg/uninit-23.c (test for excess errors) where we additionally warn gcc.dg/uninit-23.c:21:13: warning: 't4' is used uninitialized [-Wuninitialized] which I think is OK even if it's not obvious that the new warning is an improvement when you look at the obvious source. Somehow for all cases I never get the `'foo' was declared here` notes, I didn't dig why that happens but it's odd. 2021-07-22 Richard Biener PR tree-optimization/101573 * tree-ssa-uninit.c (warn_uninit_phi_uses): New function looking at uninitialized PHI arg defs in some constrained cases. (warn_uninitialized_vars): Call it. (execute_early_warn_uninitialized): Calculate dominators. * gcc.dg/uninit-pr101573.c: New testcase. * gcc.dg/uninit-15-O0.c: Adjust. * gcc.dg/uninit-15.c: Likewise. * gcc.dg/uninit-23.c: Likewise. * c-c++-common/uninit-17.c: Likewise. --- diff --git a/gcc/testsuite/c-c++-common/uninit-17.c b/gcc/testsuite/c-c++-common/uninit-17.c index fd773da78ad3..b5495366c5bc 100644 --- a/gcc/testsuite/c-c++-common/uninit-17.c +++ b/gcc/testsuite/c-c++-common/uninit-17.c @@ -9,11 +9,11 @@ static void bar(int a, int *ptr) { do { - int b; /* { dg-message "declared" } */ + int b; if (b < 40) { - ptr[0] = b; /* { dg-warning "may be used uninitialized" } */ + ptr[0] = b; } - b += 1; + b += 1; /* { dg-warning "is used uninitialized" } */ ptr++; } while (--a != 0); diff --git a/gcc/testsuite/gcc.dg/uninit-15-O0.c b/gcc/testsuite/gcc.dg/uninit-15-O0.c index a3fd2b63ba71..36d963486175 100644 --- a/gcc/testsuite/gcc.dg/uninit-15-O0.c +++ b/gcc/testsuite/gcc.dg/uninit-15-O0.c @@ -15,6 +15,6 @@ void baz(); void bar() { int j; /* { dg-message "was declared here" {} { xfail *-*-* } } */ - for (; foo(j); ++j) + for (; foo(j); ++j) /* { dg-warning "is used uninitialized" } */ baz(); } diff --git a/gcc/testsuite/gcc.dg/uninit-15.c b/gcc/testsuite/gcc.dg/uninit-15.c index 8ee10c27aba1..85cb116f3494 100644 --- a/gcc/testsuite/gcc.dg/uninit-15.c +++ b/gcc/testsuite/gcc.dg/uninit-15.c @@ -1,7 +1,7 @@ /* PR tree-optimization/17506 - We issue an uninitialized variable warning at a wrong location at + We used to issue an uninitialized variable warning at a wrong location at line 11, which is very confusing. Make sure we print out a note to - make it less confusing. (not xfailed alternative) + make it less confusing. (xfailed alternative) But it is of course ok if we warn in bar about uninitialized use of j. (not xfailed alternative) */ /* { dg-do compile } */ @@ -10,7 +10,7 @@ inline int foo (int i) { - if (i) /* { dg-warning "used uninitialized" } */ + if (i) /* { dg-warning "used uninitialized" "" { xfail *-*-* } } */ return 1; return 0; } @@ -20,7 +20,7 @@ void baz (void); void bar (void) { - int j; /* { dg-message "note: 'j' was declared here" "" } */ - for (; foo (j); ++j) /* { dg-warning "'j' is used uninitialized" "" { xfail *-*-* } } */ + int j; /* { dg-message "note: 'j' was declared here" "" { xfail *-*-* } } */ + for (; foo (j); ++j) /* { dg-warning "'j' is used uninitialized" } */ baz (); } diff --git a/gcc/testsuite/gcc.dg/uninit-23.c b/gcc/testsuite/gcc.dg/uninit-23.c index d64eb7d2ee9c..87b4e989b537 100644 --- a/gcc/testsuite/gcc.dg/uninit-23.c +++ b/gcc/testsuite/gcc.dg/uninit-23.c @@ -18,7 +18,7 @@ ql (void) int *t4 = go; /* { dg-warning "is used uninitialized" } */ l1: - *t4 = (*t4 != 0) ? 0 : 2; + *t4 = (*t4 != 0) ? 0 : 2; /* { dg-warning "is used uninitialized" } */ } if (ij != 0) diff --git a/gcc/testsuite/gcc.dg/uninit-pr101573.c b/gcc/testsuite/gcc.dg/uninit-pr101573.c new file mode 100644 index 000000000000..a574844b7914 --- /dev/null +++ b/gcc/testsuite/gcc.dg/uninit-pr101573.c @@ -0,0 +1,10 @@ +/* { dg-do compile } */ +/* { dg-options "-O0 -Wuninitialized" } */ + +int main(int argc, char **argv) +{ + int a; + for(; a < 5; ++a) /* { dg-warning "is used uninitialized" } */ + ; + return 0; +} diff --git a/gcc/tree-ssa-uninit.c b/gcc/tree-ssa-uninit.c index 148f3c2b31dd..718b32691c1a 100644 --- a/gcc/tree-ssa-uninit.c +++ b/gcc/tree-ssa-uninit.c @@ -638,6 +638,76 @@ maybe_warn_pass_by_reference (gcall *stmt, wlimits &wlims) wlims.always_executed = save_always_executed; } +/* Warn about an uninitialized PHI argument on the fallthru path to + an always executed block BB. */ + +static void +warn_uninit_phi_uses (basic_block bb) +{ + edge_iterator ei; + edge e, found = NULL, found_back = NULL; + /* Look for a fallthru and possibly a single backedge. */ + FOR_EACH_EDGE (e, ei, bb->preds) + { + /* Ignore backedges. */ + if (dominated_by_p (CDI_DOMINATORS, e->src, bb)) + { + if (found_back) + { + found = NULL; + break; + } + found_back = e; + continue; + } + if (found) + { + found = NULL; + break; + } + found = e; + } + if (!found) + return; + + basic_block succ = single_succ (ENTRY_BLOCK_PTR_FOR_FN (cfun)); + for (gphi_iterator si = gsi_start_phis (bb); !gsi_end_p (si); + gsi_next (&si)) + { + gphi *phi = si.phi (); + tree def = PHI_ARG_DEF_FROM_EDGE (phi, found); + if (TREE_CODE (def) != SSA_NAME + || !SSA_NAME_IS_DEFAULT_DEF (def) + || virtual_operand_p (def)) + continue; + /* If there's a default def on the fallthru edge PHI + value and there's a use that post-dominates entry + then that use is uninitialized and we can warn. */ + imm_use_iterator iter; + use_operand_p use_p; + gimple *use_stmt = NULL; + FOR_EACH_IMM_USE_FAST (use_p, iter, gimple_phi_result (phi)) + { + use_stmt = USE_STMT (use_p); + if (gimple_location (use_stmt) != UNKNOWN_LOCATION + && dominated_by_p (CDI_POST_DOMINATORS, succ, + gimple_bb (use_stmt)) + /* If we found a non-fallthru edge make sure the + use is inside the loop, otherwise the backedge + can serve as initialization. */ + && (!found_back + || dominated_by_p (CDI_DOMINATORS, found_back->src, + gimple_bb (use_stmt)))) + break; + use_stmt = NULL; + } + if (use_stmt) + warn_uninit (OPT_Wuninitialized, def, SSA_NAME_VAR (def), + SSA_NAME_VAR (def), + "%qD is used uninitialized", use_stmt, + UNKNOWN_LOCATION); + } +} static unsigned int warn_uninitialized_vars (bool wmaybe_uninit) @@ -652,6 +722,10 @@ warn_uninitialized_vars (bool wmaybe_uninit) { basic_block succ = single_succ (ENTRY_BLOCK_PTR_FOR_FN (cfun)); wlims.always_executed = dominated_by_p (CDI_POST_DOMINATORS, succ, bb); + + if (wlims.always_executed) + warn_uninit_phi_uses (bb); + for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi)) { gimple *stmt = gsi_stmt (gsi); @@ -3135,6 +3209,7 @@ execute_early_warn_uninitialized (void) optimization we want to warn about possible uninitialized as late as possible, thus don't do it here. However, without optimization we need to warn here about "may be uninitialized". */ + calculate_dominance_info (CDI_DOMINATORS); calculate_dominance_info (CDI_POST_DOMINATORS); warn_uninitialized_vars (/*warn_maybe_uninitialized=*/!optimize);