Hi,

This patch improves code generations for builtin arithmetic overflow operations for the aarch64 backend. As an example for a simple test case such as:

Sure for a simple test case such as:

int
f (int x, int y, int *ovf)
{
  int res;
  *ovf = __builtin_sadd_overflow (x, y, &res);
  return res;
}

Current trunk at -O2 generates

f:
	mov	w3, w0
	mov	w4, 0
	add	w0, w0, w1
	tbnz	w1, #31, .L4
	cmp	w0, w3
	blt	.L3
.L2:
	str	w4, [x2]
	ret
	.p2align 3
.L4:
	cmp	w0, w3
	ble	.L2
.L3:
	mov	w4, 1
	b	.L2


With the patch this now generates:

f:
	adds	w0, w0, w1
	cset	w1, vs
	str	w1, [x2]
	ret


Original patch from Richard Henderson:

https://gcc.gnu.org/ml/gcc-patches/2016-01/msg01903.html


Okay for trunk?

2017-05-17  Michael Collison  <michael.collison@arm.com>
	    Richard Henderson <rth@redhat.com>

	* config/aarch64/aarch64-modes.def (CC_V): New.
	* config/aarch64/aarch64-protos.h
	(aarch64_add_128bit_scratch_regs): Declare
	(aarch64_add_128bit_scratch_regs): Declare.
	(aarch64_expand_subvti): Declare.
	(aarch64_gen_unlikely_cbranch): Declare
	* config/aarch64/aarch64.c (aarch64_select_cc_mode): Test
	for signed overflow using CC_Vmode.
	(aarch64_get_condition_code_1): Handle CC_Vmode.
	(aarch64_gen_unlikely_cbranch): New function.
	(aarch64_add_128bit_scratch_regs): New function.
	(aarch64_subv_128bit_scratch_regs): New function.
	(aarch64_expand_subvti): New function.
	* config/aarch64/aarch64.md (addv<GPI>4, uaddv<GPI>4): New.
	(addti3): Create simpler code if low part is already known to be 0.
	(addvti4, uaddvti4): New.
	(*add<GPI>3_compareC_cconly_imm): New.
	(*add<GPI>3_compareC_cconly): New.
	(*add<GPI>3_compareC_imm): New.
	(*add<GPI>3_compareC): Rename from add<GPI>3_compare1; do not
	handle constants within this pattern.
	(*add<GPI>3_compareV_cconly_imm): New.
	(*add<GPI>3_compareV_cconly): New.
	(*add<GPI>3_compareV_imm): New.
	(add<GPI>3_compareV): New.
	(add<GPI>3_carryinC, add<GPI>3_carryinV): New.
	(*add<GPI>3_carryinC_zero, *add<GPI>3_carryinV_zero): New.
	(*add<GPI>3_carryinC, *add<GPI>3_carryinV): New.
	(subv<GPI>4, usubv<GPI>4): New.
	(subti): Handle op1 zero.
	(subvti4, usub4ti4): New.
	(*sub<GPI>3_compare1_imm): New.
	(sub<GPI>3_carryinCV): New.
	(*sub<GPI>3_carryinCV_z1_z2, *sub<GPI>3_carryinCV_z1): New.
	(*sub<GPI>3_carryinCV_z2, *sub<GPI>3_carryinCV): New.
	* testsuite/gcc.target/arm/builtin_sadd_128.c: New testcase.
	* testsuite/gcc.target/arm/builtin_saddl.c: New testcase.
	* testsuite/gcc.target/arm/builtin_saddll.c: New testcase.
	* testsuite/gcc.target/arm/builtin_uadd_128.c: New testcase.
	* testsuite/gcc.target/arm/builtin_uaddl.c: New testcase.
	* testsuite/gcc.target/arm/builtin_uaddll.c: New testcase.
	* testsuite/gcc.target/arm/builtin_ssub_128.c: New testcase.
	* testsuite/gcc.target/arm/builtin_ssubl.c: New testcase.
	* testsuite/gcc.target/arm/builtin_ssubll.c: New testcase.
	* testsuite/gcc.target/arm/builtin_usub_128.c: New testcase.
	* testsuite/gcc.target/arm/builtin_usubl.c: New testcase.
	* testsuite/gcc.target/arm/builtin_usubll.c: New testcase.