Fold single imm use of a FMA if it is a negation [PR95060]

Fold single imm use of a FMA if it is a negation [PR95060]

match.pd already has simplifications for negation of a FMA (FMS, FNMA, FNMS)
call if it is single use, but when the widening_mul pass discovers FMAs,
nothing folds the statements anymore.

So, the following patch adjusts the widening_mul pass to handle that.

I had to adjust quite a lot of tests, because they have in them nested FMAs
(one FMA feeding another one) and the patch results in some (equivalent) changes
in the chosen instructions, previously the negation of one FMA's result
would result in the dependent FMA being adjusted for the negation, but now
instead the first FMA is adjusted.

2020-05-13  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/95060
	* tree-ssa-math-opts.c (convert_mult_to_fma_1): Fold a NEGATE_EXPR
	if it is the single use of the FMA internal builtin.

	* gcc.target/i386/avx512f-pr95060.c: New test.
	* gcc.target/i386/fma_double_1.c: Adjust expected insn counts.
	* gcc.target/i386/fma_double_2.c: Likewise.
	* gcc.target/i386/fma_double_3.c: Likewise.
	* gcc.target/i386/fma_double_4.c: Likewise.
	* gcc.target/i386/fma_double_5.c: Likewise.
	* gcc.target/i386/fma_double_6.c: Likewise.
	* gcc.target/i386/fma_float_1.c: Likewise.
	* gcc.target/i386/fma_float_2.c: Likewise.
	* gcc.target/i386/fma_float_3.c: Likewise.
	* gcc.target/i386/fma_float_4.c: Likewise.
	* gcc.target/i386/fma_float_5.c: Likewise.
	* gcc.target/i386/fma_float_6.c: Likewise.
	* gcc.target/i386/l_fma_double_1.c: Likewise.
	* gcc.target/i386/l_fma_double_2.c: Likewise.
	* gcc.target/i386/l_fma_double_3.c: Likewise.
	* gcc.target/i386/l_fma_double_4.c: Likewise.
	* gcc.target/i386/l_fma_double_5.c: Likewise.
	* gcc.target/i386/l_fma_double_6.c: Likewise.
	* gcc.target/i386/l_fma_float_1.c: Likewise.
	* gcc.target/i386/l_fma_float_2.c: Likewise.
	* gcc.target/i386/l_fma_float_3.c: Likewise.
	* gcc.target/i386/l_fma_float_4.c: Likewise.
	* gcc.target/i386/l_fma_float_5.c: Likewise.
	* gcc.target/i386/l_fma_float_6.c: Likewise.