common.opt: Add fstrict-overflow.

./:	* common.opt: Add fstrict-overflow.
	* opts.c (decode_options): Set flag_strict_overflow if -O2.
	* flags.h (TYPE_OVERFLOW_WRAPS): Define.
	(TYPE_OVERFLOW_UNDEFINED): Define.
	(TYPE_OVERFLOW_TRAPS): Define.  This replaces TYPE_TRAP_SIGNED.
	Replace all uses.
	* tree.h (TYPE_TRAP_SIGNED): Don't define.
	* fold-const.c (negate_expr_p): Use TYPE_OVERFLOW_UNDEFINED.
	(fold_negate_expr): Likewise.
	(make_range): Likewise.
	(extract_muldiv_1): Likewise.
	(maybe_canonicalize_comparison): Likewise.
	(fold_comparison): Likewise.
	(fold_binary): Likewise.
	(tree_expr_nonnegative_p): Likewise.
	(tree_expr_nonzero_p): Likewise.
	* tree-vrp.c (compare_values): Likewise.
	(extract_range_from_binary_expr): Likewise.
	(extract_range_from_unary_expr): Likewise.
	* tree-ssa-loop-niter.c (infer_loop_bounds_from_signedness):
	Likewise.
	(nowrap_type_p): Likewise.
	* tree-scalar-evolution.c (simple_iv): Likewise.
	* fold-const.c (negate_expr_p): Use TYPE_OVERFLOW_WRAPS.
	(build_range_check): Likewise.
	(extract_muldiv_1): Likewise.
	(fold_comparison): Likewise.
	* tree-vrp.c (vrp_int_const_binop): Likewise.
	(extract_range_from_unary_expr): Likewise.
	* convert.c (convert_to_integer): Likewise.
	* fold-const.c (fold_negate_expr): Use TYPE_OVERFLOW_TRAPS.
	(fold_comparison): Likewise.
	(fold_binary): Likewise.
	* optabs.c (optab_for_tree_code): Likewise.
	* tree-vectorizer.c (vect_is_simple_reduction): Likewise.
	* simplify-rtx.c (simplify_const_relational_operation): Check
	flag_strict_overflow and flag_trapv.
	(simplify_const_relational_operation): Likewise.
	* doc/invoke.texi (Option Summary): Mention -fstrict-overflow.
	(Optimize Options): Add -fstrict-overflow to -O2 list.  Document
	-fstrict-overflow.
testsuite/:
	* gcc.dg/strict-overflow-1.c: New test.
	* gcc.dg/no-strict-overflow-1.c: New test.
	* gcc.dg/strict-overflow-2.c: New test.
	* gcc.dg/no-strict-overflow-2.c: New test.
	* gcc.dg/strict-overflow-3.c: New test.
	* gcc.dg/no-strict-overflow-3.c: New test.
	* gcc.dg/strict-overflow-4.c: New test.
	* gcc.dg/no-strict-overflow-4.c: New test.
	* gcc.dg/fold-mod-1.c: Add -fstrict-overflow option.
	* gcc.dg/pr15784-1.c: Likewise.
	* gcc.dg/pr20922-1.c: Likewise.
	* gcc.dg/pr20922-3.c: Likewise.
	* gcc.dg/pr20922-4.c: Likewise.
	* gcc.dg/pr20922-6.c: Likewise.
	* gcc.dg/compare-4.c: Likewise.
	* gcc.dg/torture/pr26898-1.c: Likewise.
	* gcc.dg/tree-ssa/divide-1.c: Likewise.
	* gcc.dg/tree-ssa/divide-2.c: Likewise.
	* gcc.dg/tree-ssa/divide-3.c: Likewise.
	* gcc.dg/tree-ssa/divide-4.c: Likewise.
	* gcc.dg/tree-ssa/pr14490-1.c: Likewise.
	* gcc.dg/tree-ssa/pr14490-3.c: Likewise.
	* gcc.dg/tree-ssa/pr21082.c: Likewise.
	* gcc.dg/tree-ssa/pr26899.c: Likewise.
	* g++.dg/tree-ssa/pr21082.C: Likewise.

From-SVN: r121254

1 files changed, 28 insertions, 2 deletions

diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index fee5871dc89..eb55c9b321a 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -341,7 +341,7 @@ Objective-C and Objective-C++ Dialects}.
 -fsched2-use-traces -fsee -freschedule-modulo-scheduled-loops @gol
 -fsection-anchors  -fsignaling-nans  -fsingle-precision-constant @gol
 -fstack-protector  -fstack-protector-all @gol
--fstrict-aliasing  -ftracer  -fthread-jumps @gol
+-fstrict-aliasing  -fstrict-overflow  -ftracer  -fthread-jumps @gol
 -funroll-all-loops  -funroll-loops  -fpeel-loops @gol
 -fsplit-ivs-in-unroller -funswitch-loops @gol
 -fvariable-expansion-in-unroller @gol
@@ -4635,7 +4635,7 @@ also turns on the following optimization flags:
 -fschedule-insns  -fschedule-insns2 @gol
 -fsched-interblock  -fsched-spec @gol
 -fregmove @gol
--fstrict-aliasing @gol
+-fstrict-aliasing -fstrict-overflow @gol
 -fdelete-null-pointer-checks @gol
 -freorder-blocks  -freorder-functions @gol
 -falign-functions  -falign-jumps @gol
@@ -5465,6 +5465,32 @@ int f() @{
 
 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
 
+@item -fstrict-overflow
+@opindex fstrict-overflow
+Allow the compiler to assume strict signed overflow rules, depending
+on the language being compiled.  For C (and C++) this means that
+overflow when doing arithmetic with signed numbers is undefined, which
+means that the compiler may assume that it will not happen.  This
+permits various optimizations.  For example, the compiler will assume
+that an expression like @code{i + 10 > i} will always be true for
+signed @code{i}.  This assumption is only valid if signed overflow is
+undefined, as the expression is false if @code{i + 10} overflows when
+using twos complement arithmetic.  When this option is in effect any
+attempt to determine whether an operation on signed numbers will
+overflow must be written carefully to not actually involve overflow.
+
+See also the @option{-fwrapv} option.  Using @option{-fwrapv} means
+that signed overflow is fully defined: it wraps.  When
+@option{-fwrapv} is used, there is no difference between
+@option{-fstrict-overflow} and @option{-fno-strict-overflow}.  With
+@option{-fwrapv} certain types of overflow are permitted.  For
+example, if the compiler gets an overflow when doing arithmetic on
+constants, the overflowed value can still be used with
+@option{-fwrapv}, but not otherwise.
+
+The @option{-fstrict-overflow} option is enabled at levels
+@option{-O2}, @option{-O3}, @option{-Os}.
+
 @item -falign-functions
 @itemx -falign-functions=@var{n}
 @opindex falign-functions