middle-end: optimize fneg (fabs (x)) to copysign (x, -1) [PR109154]

middle-end: optimize fneg (fabs (x)) to copysign (x, -1) [PR109154]

This patch transforms fneg (fabs (x)) into copysign (x, -1) which is more
canonical and allows a target to expand this sequence efficiently.  Such
sequences are common in scientific code working with gradients.

There is an existing canonicalization of copysign (x, -1) to fneg (fabs (x))
which I remove since this is a less efficient form.  The testsuite is also
updated in light of this.

gcc/ChangeLog:

	PR tree-optimization/109154
	* match.pd: Add new neg+abs rule, remove inverse copysign rule.

gcc/testsuite/ChangeLog:

	PR tree-optimization/109154
	* gcc.dg/fold-copysign-1.c: Updated.
	* gcc.dg/pr55152-2.c: Updated.
	* gcc.dg/tree-ssa/abs-4.c: Updated.
	* gcc.dg/tree-ssa/backprop-6.c: Updated.
	* gcc.dg/tree-ssa/copy-sign-2.c: Updated.
	* gcc.dg/tree-ssa/mult-abs-2.c: Updated.
	* gcc.target/aarch64/fneg-abs_1.c: New test.
	* gcc.target/aarch64/fneg-abs_2.c: New test.
	* gcc.target/aarch64/fneg-abs_3.c: New test.
	* gcc.target/aarch64/fneg-abs_4.c: New test.
	* gcc.target/aarch64/sve/fneg-abs_1.c: New test.
	* gcc.target/aarch64/sve/fneg-abs_2.c: New test.
	* gcc.target/aarch64/sve/fneg-abs_3.c: New test.
	* gcc.target/aarch64/sve/fneg-abs_4.c: New test.