[PATCH]: Rewrite i387 fptan patterns (+ optimize reg-stack.c handling of double-output insns)

["Uros Bizjak" <ubizjak at gmail dot com>]

Hello!

This patch rewrites i387 fptan patterns in order to correctly model
load of constant 1.0 into top stack slot. This way, we can get rid of
hacky peephole2 patterns that were used to optimize "fptan; fstp0;
fld1" sequences into plain fptan. Having new fptan patterns, gcc knows
that 1.0 is loaded into top stack slot and uses it according to its
generic rules.

As an example, following source:

double test(double x) {
 return 1.0 / sqrt (tan(x) + 1.0);
}

compiles into (-O2 -ffast-math -fomit-frame-pointer):
test:
       fldl    4(%esp)
       fptan
       fadd    %st, %st(1)
       fxch    %st(1)
       fsqrt
       fdivrp  %st, %st(1)
       ret

This patch also cleans reg-stack.c handling of double-output stack
instructions. First part of instruction now uses the same code as
normal single-output instruction, while the code to fix-up stack is
now part of second-part handling (and simplified considerably). The
loading of 1.0 in fptan instruction is handled by generic move code,
which was not prepared to load 1.0 into "live" top stack slot (there
is an argument for fptan). This case was special-cased in the generic
code (with a lenghty comment, why this is necessary).

Patch was bootstrapped and regression tested on i686-pc-linux-gnu for
c, c++ and fortran.

Patch needs middle-end approval for reg-stack.c changes.

2007-01-16  Uros Bizjak  <ubizjak@gmail.com>

	* reg-stack.c (subst_stack_regs_pat) [UNSPEC_SINCOS_COS,
	UNSPEC_XTRACT_FRACT]: Use generic code for instructions that
	operate on the top of stack.
	[UNSPEC_SINCOS_SIN, UNSPEC_XTRACT_EXP, UNSPEC_TAN]: Rewrite
	register handling of instructions that output to the second
	stack slot.
	[UNSPEC_TAN_ONE, UNSPEC_TAN_TAN]: Remove.
	(move_for_stack_reg): Special-case check for dead destination
	stack slot for constant load of 1.0 inside UNSPEC_TAN.

	* config/i386/i386.md (UNSPEC_TAN): New constant.
	(UNSPEC_TAN_ONE, UNSPEC_TAN_TAN): Remove.
	(fptanxf4_i387, fptan_extend<mode>xf4_i387): New patterns
	to correctly model move of constant 1.0 to top stack slot.
	(*tandf3_1, *tansf3_1, *tanxf3_1): Remove insn patterns.
	(unnamed peephole2 pattern): Remove corresponding peephole2
	pattern that optimizes tan insn and loading of constant 1.0.
	(tanxf2): Use fptanxf4_i387.
	(tan<mode>2): Rename from tansf2 and tandf2 and macroize insn
	patterns using X87MODEF12 mode macro.  Use fptan_extend<mode>xf4_i387
	and truncate result to requested mode.  Use SSE_FLOAT_MODE_P to
	disable patterns for SSE math.
	(sincos<mode>3): Use truncxf<mode>2_i387_noop for truncation.
	(fyl2x_extend<mode>xf3_i387): Use X87MODEF12 for operand 1.

testsuite/ChangeLog:

2007-01-16  Uros Bizjak  <ubizjak@gmail.com>

	* gcc.target/i386/387-8.c: Update comment about optimizing
	inherent load of 1.0 of fptan instruction.

Uros.

Attachment: i386-tan.c
Description: Text document