This middle-end patch resolves PR c/106264 which is a spurious warning
regression caused by the tree-level expansion of modf, frexp and remquo
producing "expression has no-effect" when the built-in function's result
is ignored. When these built-ins were first expanded at tree-level,
fold_builtin_n would blindly set TREE_NO_WARNING for all built-ins.
Now that we're more discerning, we should precisely set TREE_NO_WARNING
selectively on those COMPOUND_EXPRs that need them.
This patch has been tested on x86_64-pc-linux-gnu with make bootstrap
and make -k check with no new failures. Ok for mainline?
2022-07-16 Roger Sayle
gcc/ChangeLog
PR c/106264
* builtins.cc (fold_builtin_frexp): Set TREE_NO_WARNING on
COMPOUND_EXPR to silence spurious warning if result isn't used.
(fold_builtin_modf): Likewise.
(do_mpfr_remquo): Likewise.
gcc/testsuite/ChangeLog
PR c/106264
* gcc.dg/pr106264.c: New test case.
Thanks in advance,
Roger
--
diff --git a/gcc/builtins.cc b/gcc/builtins.cc
index 35b9197..c745777 100644
--- a/gcc/builtins.cc
+++ b/gcc/builtins.cc
@@ -8625,7 +8625,7 @@ fold_builtin_frexp (location_t loc, tree arg0, tree arg1,
tree rettype)
if (TYPE_MAIN_VARIANT (TREE_TYPE (arg1)) == integer_type_node)
{
const REAL_VALUE_TYPE *const value = TREE_REAL_CST_PTR (arg0);
- tree frac, exp;
+ tree frac, exp, res;
switch (value->cl)
{
@@ -8656,7 +8656,9 @@ fold_builtin_frexp (location_t loc, tree arg0, tree arg1,
tree rettype)
/* Create the COMPOUND_EXPR (*arg1 = trunc, frac). */
arg1 = fold_build2_loc (loc, MODIFY_EXPR, rettype, arg1, exp);
TREE_SIDE_EFFECTS (arg1) = 1;
- return fold_build2_loc (loc, COMPOUND_EXPR, rettype, arg1, frac);
+ res = fold_build2_loc (loc, COMPOUND_EXPR, rettype, arg1, frac);
+ TREE_NO_WARNING (res) = 1;
+ return res;
}
return NULL_TREE;
@@ -8682,6 +8684,7 @@ fold_builtin_modf (location_t loc, tree arg0, tree arg1,
tree rettype)
{
const REAL_VALUE_TYPE *const value = TREE_REAL_CST_PTR (arg0);
REAL_VALUE_TYPE trunc, frac;
+ tree res;
switch (value->cl)
{
@@ -8711,8 +8714,10 @@ fold_builtin_modf (location_t loc, tree arg0, tree arg1,
tree rettype)
arg1 = fold_build2_loc (loc, MODIFY_EXPR, rettype, arg1,
build_real (rettype, trunc));
TREE_SIDE_EFFECTS (arg1) = 1;
- return fold_build2_loc (loc, COMPOUND_EXPR, rettype, arg1,
- build_real (rettype, frac));
+ res = fold_build2_loc (loc, COMPOUND_EXPR, rettype, arg1,
+build_real (rettype, frac));
+ TREE_NO_WARNING (res) = 1;
+ return res;
}
return NULL_TREE;
@@ -10673,8 +10678,10 @@ do_mpfr_remquo (tree arg0, tree arg1, tree arg_quo)
integer_quo));
TREE_SIDE_EFFECTS (result_quo) = 1;
/* Combine the quo assignment with the rem. */
- result = non_lvalue (fold_build2 (COMPOUND_EXPR, type,
- result_quo, result_rem));
+ result = fold_build2 (COMPOUND_EXPR, type,
+ result_quo, result_rem);
+ TREE_NO_WARNING (result) = 1;
+ result = non_lvalue (result);
}
}
}
diff --git a/gcc/testsuite/gcc.dg/pr106264.c b/gcc/testsuite/gcc.dg/pr106264.c
new file mode 100644
index 000..6b4af49
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr106264.c
@@ -0,0 +1,27 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -Wall" } */
+double frexp (double, int*);
+double modf (double, double*);
+double remquo (double, double, int*);
+
+int f (void)
+{
+ int y;
+ frexp (1.0, );
+ return y;
+}
+
+double g (void)
+{
+ double y;
+ modf (1.0, );
+ return y;
+}
+
+int h (void)
+{
+ int y;
+ remquo (1.0, 1.0, );
+ return y;
+}
+
