c: Fix up -Wunused-but-set-* warnings for _Atomics [PR99588]
As the following testcases show, compared to -D_Atomic= case we have many -Wunused-but-set-* warning false positives. When an _Atomic variable/parameter is read, we call mark_exp_read on it in convert_lvalue_to_rvalue, but build_atomic_assign does not. For consistency with the non-_Atomic case where we mark_exp_read the lhs for lhs op= ... but not for lhs = ..., this patch does that too. But furthermore we need to pattern match the trees emitted by _Atomic store, so that _Atomic store itself is not marked as being a variable read, but when the result of the store is used, we mark it. 2021-03-19 Jakub Jelinek <jakub@redhat.com> PR c/99588 * c-typeck.c (mark_exp_read): Recognize what build_atomic_assign with modifycode NOP_EXPR produces and mark the _Atomic var as read if found. (build_atomic_assign): For modifycode of NOP_EXPR, use COMPOUND_EXPRs rather than STATEMENT_LIST. Otherwise call mark_exp_read on lhs. Set TREE_SIDE_EFFECTS on the TARGET_EXPR. * gcc.dg/Wunused-var-5.c: New test. * gcc.dg/Wunused-var-6.c: New test.
This commit is contained in:
Jakub Jelinek
parent
e5d74554b5
commit
3279a9a5a9
3 changed files with 97 additions and 6 deletions
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@ -1968,6 +1968,50 @@ mark_exp_read (tree exp)
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mark_exp_read (TREE_OPERAND (exp, 0));
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break;
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case COMPOUND_EXPR:
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/* Pattern match what build_atomic_assign produces with modifycode
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NOP_EXPR. */
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if (VAR_P (TREE_OPERAND (exp, 1))
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&& DECL_ARTIFICIAL (TREE_OPERAND (exp, 1))
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&& TREE_CODE (TREE_OPERAND (exp, 0)) == COMPOUND_EXPR)
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{
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tree t1 = TREE_OPERAND (TREE_OPERAND (exp, 0), 0);
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tree t2 = TREE_OPERAND (TREE_OPERAND (exp, 0), 1);
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if (TREE_CODE (t1) == TARGET_EXPR
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&& TARGET_EXPR_SLOT (t1) == TREE_OPERAND (exp, 1)
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&& TREE_CODE (t2) == CALL_EXPR)
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{
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tree fndecl = get_callee_fndecl (t2);
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tree arg = NULL_TREE;
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if (fndecl
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&& TREE_CODE (fndecl) == FUNCTION_DECL
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&& fndecl_built_in_p (fndecl, BUILT_IN_NORMAL)
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&& call_expr_nargs (t2) >= 2)
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switch (DECL_FUNCTION_CODE (fndecl))
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{
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case BUILT_IN_ATOMIC_STORE:
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arg = CALL_EXPR_ARG (t2, 1);
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break;
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case BUILT_IN_ATOMIC_STORE_1:
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case BUILT_IN_ATOMIC_STORE_2:
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case BUILT_IN_ATOMIC_STORE_4:
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case BUILT_IN_ATOMIC_STORE_8:
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case BUILT_IN_ATOMIC_STORE_16:
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arg = CALL_EXPR_ARG (t2, 0);
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break;
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default:
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break;
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}
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if (arg)
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{
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STRIP_NOPS (arg);
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if (TREE_CODE (arg) == ADDR_EXPR
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&& DECL_P (TREE_OPERAND (arg, 0))
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&& TYPE_ATOMIC (TREE_TYPE (TREE_OPERAND (arg, 0))))
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mark_exp_read (TREE_OPERAND (arg, 0));
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}
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}
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}
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/* FALLTHRU */
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case C_MAYBE_CONST_EXPR:
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mark_exp_read (TREE_OPERAND (exp, 1));
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break;
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@ -4065,7 +4109,7 @@ build_atomic_assign (location_t loc, tree lhs, enum tree_code modifycode,
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vec<tree, va_gc> *params;
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tree val, nonatomic_lhs_type, nonatomic_rhs_type, newval, newval_addr;
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tree old, old_addr;
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tree compound_stmt;
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tree compound_stmt = NULL_TREE;
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tree stmt, goto_stmt;
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tree loop_label, loop_decl, done_label, done_decl;
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@ -4086,7 +4130,15 @@ build_atomic_assign (location_t loc, tree lhs, enum tree_code modifycode,
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/* Create a compound statement to hold the sequence of statements
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with a loop. */
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compound_stmt = c_begin_compound_stmt (false);
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if (modifycode != NOP_EXPR)
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{
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compound_stmt = c_begin_compound_stmt (false);
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/* For consistency with build_modify_expr on non-_Atomic,
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mark the lhs as read. Also, it would be very hard to match
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such expressions in mark_exp_read. */
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mark_exp_read (lhs);
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}
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/* Remove any excess precision (which is only present here in the
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case of compound assignments). */
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@ -4112,13 +4164,16 @@ build_atomic_assign (location_t loc, tree lhs, enum tree_code modifycode,
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TREE_NO_WARNING (val) = 1;
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rhs = build4 (TARGET_EXPR, nonatomic_rhs_type, val, rhs, NULL_TREE,
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NULL_TREE);
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TREE_SIDE_EFFECTS (rhs) = 1;
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SET_EXPR_LOCATION (rhs, loc);
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add_stmt (rhs);
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if (modifycode != NOP_EXPR)
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add_stmt (rhs);
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/* NOP_EXPR indicates it's a straight store of the RHS. Simply issue
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an atomic_store. */
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if (modifycode == NOP_EXPR)
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{
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compound_stmt = rhs;
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/* Build __atomic_store (&lhs, &val, SEQ_CST) */
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rhs = build_unary_op (loc, ADDR_EXPR, val, false);
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fndecl = builtin_decl_explicit (BUILT_IN_ATOMIC_STORE);
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@ -4126,10 +4181,9 @@ build_atomic_assign (location_t loc, tree lhs, enum tree_code modifycode,
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params->quick_push (rhs);
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params->quick_push (seq_cst);
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func_call = c_build_function_call_vec (loc, vNULL, fndecl, params, NULL);
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add_stmt (func_call);
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/* Finish the compound statement. */
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compound_stmt = c_end_compound_stmt (loc, compound_stmt, false);
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compound_stmt = build2 (COMPOUND_EXPR, void_type_node,
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compound_stmt, func_call);
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/* VAL is the value which was stored, return a COMPOUND_STMT of
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the statement and that value. */
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23
gcc/testsuite/gcc.dg/Wunused-var-5.c
Normal file
23
gcc/testsuite/gcc.dg/Wunused-var-5.c
Normal file
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@ -0,0 +1,23 @@
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/* PR c/99588 */
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/* { dg-do compile } */
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/* { dg-options "-std=c11 -Wunused-but-set-variable" } */
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void bar (int, ...);
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void f1 (void) { static _Atomic int x = 0; bar (0, x); }
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void f2 (void) { static _Atomic int x = 0; bar (0, x += 1); }
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void f3 (void) { static _Atomic int x = 0; bar (x); }
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void f4 (void) { static _Atomic int x = 0; bar (x += 1); }
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void f5 (void) { static _Atomic int x = 0; bar (x = 1); }
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void f6 (void) { static _Atomic int x = 0; x = 1; } /* { dg-warning "variable 'x' set but not used" } */
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void f7 (void) { static _Atomic int x = 0; x += 3; }
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void f8 (void) { _Atomic int x = 0; bar (0, x); }
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void f9 (void) { _Atomic int x = 0; bar (0, x += 1); }
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void f10 (void) { _Atomic int x = 0; bar (x); }
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void f11 (void) { _Atomic int x = 0; bar (x += 1); }
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void f12 (void) { _Atomic int x = 0; bar (x = 1); }
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void f13 (void) { _Atomic int x = 0; x = 1; } /* { dg-warning "variable 'x' set but not used" } */
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void f14 (void) { _Atomic int x = 0; x += 3; }
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void f15 (void) { _Atomic int x = 0; int y = 3; x += y; }
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void f16 (void) { _Atomic int x = 0; int y = 3; bar (x += y); }
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void f17 (void) { _Atomic int x = 0; int y = 3; x = y; } /* { dg-warning "variable 'x' set but not used" } */
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void f18 (void) { _Atomic int x = 0; int y = 3; bar (x = y); }
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14
gcc/testsuite/gcc.dg/Wunused-var-6.c
Normal file
14
gcc/testsuite/gcc.dg/Wunused-var-6.c
Normal file
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@ -0,0 +1,14 @@
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/* PR c/99588 */
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/* { dg-do compile } */
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/* { dg-options "-std=c11 -Wunused-but-set-variable" } */
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void bar (int, ...);
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struct S { int a, b, c; };
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typedef _Atomic struct S T;
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void
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foo (void)
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{
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static T x = (struct S) { 0, 0, 0 }; /* { dg-bogus "set but not used" } */
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bar (0, x = (struct S) { 1, 1, 1 });
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}
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