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PR c/106264: Silence warnings from __builtin_modf et al. 

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 call suppress_warning
selectively on those COMPOUND_EXPRs that need them.

2022-07-19  Roger Sayle  <roger@nextmovesoftware.com>
	    Richard Biener  <rguenther@suse.de>

gcc/ChangeLog
	PR c/106264
	* builtins.cc (fold_builtin_frexp): Call suppress_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.
This commit is contained in:
Roger Sayle 2022-07-19 08:39:43 +01:00
parent 2180cdd8a0
commit 40f6e59122
2 changed files with 40 additions and 6 deletions
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19
gcc/builtins.cc
View File

@ -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);
suppress_warning (res, OPT_Wunused_value);
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));
suppress_warning (res, OPT_Wunused_value);
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);
suppress_warning (result, OPT_Wunused_value);
result = non_lvalue (result);
}
}
}

27
gcc/testsuite/gcc.dg/pr106264.c Normal file
View File

@ -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, &y);
return y;
}
double g (void)
{
double y;
modf (1.0, &y);
return y;
}
int h (void)
{
int y;
remquo (1.0, 1.0, &y);
return y;
}