Hello!
One notable omission from x87 rounding sequences is plain round(),
since x87 does not support round-to-nearest, away-from-zero directly.
However, this function can be synthesized as round(a) = sgn(a) *
floor(fabs(a) + 0.5). Fortunately, we have all building blocks ready
in i386.md, we should just wire them correctly.
The x87 expansion is protected with flag_unsafe_math_optimizations,
since the input range is reduced (true?) due to addition - OTOH, insn
that calculates floor is protected by this flag anyway.
2011-08-08 Uros Bizjak <ubiz...@gmail.com>
* config/i386/i386.c (ix86_emit_i387_round): New function.
* config/i386/i386-protos.h (ix86_emit_i387_round): Declare.
* config/i386/i386.md (round<mode>2): Use X87MODEF mode iterator.
Use ix86_emit_i387_round to expand round function for i387 math.
Patch was bootstrapped and regression tested on x86_64-pc-linux-gnu.
It also computes correctly +-NaN, +-Inf and all inputs I have thrown
in.
Any comments?
Uros.
Index: i386.md
===================================================================
--- i386.md (revision 177572)
+++ i386.md (working copy)
@@ -14362,17 +14396,31 @@
})
(define_expand "round<mode>2"
- [(match_operand:MODEF 0 "register_operand" "")
- (match_operand:MODEF 1 "nonimmediate_operand" "")]
- "SSE_FLOAT_MODE_P (<MODE>mode) && TARGET_SSE_MATH
- && !flag_trapping_math && !flag_rounding_math"
+ [(match_operand:X87MODEF 0 "register_operand" "")
+ (match_operand:X87MODEF 1 "nonimmediate_operand" "")]
+ "(TARGET_USE_FANCY_MATH_387
+ && (!(SSE_FLOAT_MODE_P (<MODE>mode) && TARGET_SSE_MATH)
+ || TARGET_MIX_SSE_I387)
+ && flag_unsafe_math_optimizations)
+ || (SSE_FLOAT_MODE_P (<MODE>mode) && TARGET_SSE_MATH
+ && !flag_trapping_math && !flag_rounding_math)"
{
if (optimize_insn_for_size_p ())
FAIL;
- if (TARGET_64BIT || (<MODE>mode != DFmode))
- ix86_expand_round (operand0, operand1);
+
+ if (SSE_FLOAT_MODE_P (<MODE>mode) && TARGET_SSE_MATH
+ && !flag_trapping_math && !flag_rounding_math)
+ {
+ if (TARGET_64BIT || (<MODE>mode != DFmode))
+ ix86_expand_round (operands[0], operands[1]);
+ else
+ ix86_expand_rounddf_32 (operands[0], operands[1]);
+ }
else
- ix86_expand_rounddf_32 (operand0, operand1);
+ {
+ operands[1] = force_reg (<MODE>mode, operands[1]);
+ ix86_emit_i387_round (operands[0], operands[1]);
+ }
DONE;
})
Index: i386-protos.h
===================================================================
--- i386-protos.h (revision 177572)
+++ i386-protos.h (working copy)
@@ -163,6 +163,7 @@ extern void x86_emit_floatuns (rtx [2]);
extern void ix86_emit_fp_unordered_jump (rtx);
extern void ix86_emit_i387_log1p (rtx, rtx);
+extern void ix86_emit_i387_round (rtx, rtx);
extern void ix86_emit_swdivsf (rtx, rtx, rtx, enum machine_mode);
extern void ix86_emit_swsqrtsf (rtx, rtx, enum machine_mode, bool);
Index: i386.c
===================================================================
--- i386.c (revision 177572)
+++ i386.c (working copy)
@@ -31722,6 +31729,76 @@ void ix86_emit_i387_log1p (rtx op0, rtx op1)
emit_label (label2);
}
+/* Emit code for round calculation. */
+void ix86_emit_i387_round (rtx op0, rtx op1)
+{
+ enum machine_mode mode = GET_MODE (op0);
+ rtx e1, e2, res, tmp0, tmp1, half;
+ rtx scratch = gen_reg_rtx (HImode);
+ rtx flags = gen_rtx_REG (CCNOmode, FLAGS_REG);
+ rtx jump_label = gen_label_rtx ();
+ rtx insn;
+
+ e1 = gen_reg_rtx (mode);
+ e2 = gen_reg_rtx (mode);
+ res = gen_reg_rtx (mode);
+
+ half = CONST_DOUBLE_FROM_REAL_VALUE (dconsthalf, mode);
+
+ /* round(a) = sgn(a) * floor(fabs(a) + 0.5) */
+
+ /* scratch = fxam(op1) */
+ emit_insn (gen_rtx_SET (VOIDmode, scratch,
+ gen_rtx_UNSPEC (HImode, gen_rtvec (1, op1),
+ UNSPEC_FXAM)));
+ /* e1 = fabs(op1) */
+ emit_insn (gen_rtx_SET (VOIDmode, e1,
+ gen_rtx_ABS (mode, op1)));
+
+ /* e2 = e1 + 0.5 */
+ half = force_reg (mode, half);
+ emit_insn (gen_rtx_SET (VOIDmode, e2,
+ gen_rtx_PLUS (mode, e1, half)));
+
+ /* res = floor(e2) */
+ if (mode != XFmode)
+ {
+ tmp0 = gen_reg_rtx (XFmode);
+ tmp1 = gen_reg_rtx (XFmode);
+
+ emit_insn (gen_rtx_SET (VOIDmode, tmp1,
+ gen_rtx_FLOAT_EXTEND (XFmode, e2)));
+ }
+ else
+ tmp0 = res, tmp1 = e2;
+
+ emit_insn (gen_frndintxf2_floor (tmp0, tmp1));
+
+ if (mode != XFmode)
+ emit_insn (gen_rtx_SET (VOIDmode, res,
+ gen_rtx_UNSPEC (mode, gen_rtvec (1, tmp0),
+ UNSPEC_TRUNC_NOOP)));
+ /* flags = signbit(a) */
+ emit_insn (gen_testqi_ext_ccno_0 (scratch, GEN_INT (0x02)));
+
+ /* if (flags) then res = -res */
+ tmp0 = gen_rtx_IF_THEN_ELSE (VOIDmode,
+ gen_rtx_EQ (VOIDmode, flags, const0_rtx),
+ gen_rtx_LABEL_REF (VOIDmode, jump_label),
+ pc_rtx);
+ insn = emit_jump_insn (gen_rtx_SET (VOIDmode, pc_rtx, tmp0));
+ predict_jump (REG_BR_PROB_BASE * 50 / 100);
+ JUMP_LABEL (insn) = jump_label;
+
+ emit_insn (gen_rtx_SET (VOIDmode, res,
+ gen_rtx_NEG (mode, res)));
+
+ emit_label (jump_label);
+ LABEL_NUSES (jump_label) = 1;
+
+ emit_move_insn (op0, res);
+}
+
/* Output code to perform a Newton-Rhapson approximation of a single precision
floating point divide [http://en.wikipedia.org/wiki/N-th_root_algorithm].
*/
