As at r2.2 of the RISC-V ISA specification[1] (equivalent to version 2.0
of the "F" and "D" standard architecture extensions for single-precision
and double-precision floating-point respectively) the FMIN and FMAX
machine instructions fully match our requirement for the `fminM3' and
`fmaxM3' standard RTL patterns:
"For FMIN and FMAX, if at least one input is a signaling NaN, or if both
inputs are quiet NaNs, the result is the canonical NaN. If one operand
is a quiet NaN and the other is not a NaN, the result is the non-NaN
operand."
suitably for the IEEE 754-2008 `minNum' and `maxNum' operations.
However we only define `sminM3' and `smaxM3' standard RTL patterns to
produce the FMIN and FMAX machine instructions, which in turn causes the
`__builtin_fmin' and `__builtin_fmax' family of intrinsics to emit the
corresponding libcalls rather than the relevant machine instructions.
This is according to earlier revisions of the RISC-V ISA specification,
which we however do not support anymore, as from commit 4b81528241ca
("RISC-V: Support version controling for ISA standard extensions").
As from r20190608 of the RISC-V ISA specification (equivalent to version
2.2 of the "F" and "D" standard ISA extensions for single-precision and
double-precision floating-point respectively) the definition of the FMIN
and FMAX machine instructions has been updated[2]:
"Defined the signed-zero behavior of FMIN.fmt and FMAX.fmt, and changed
their behavior on signaling-NaN inputs to conform to the minimumNumber
and maximumNumber operations in the proposed IEEE 754-201x
specification."
and specifically[3]:
"Floating-point minimum-number and maximum-number instructions FMIN.S
and FMAX.S write, respectively, the smaller or larger of rs1 and rs2 to
rd. For the purposes of these instructions only, the value -0.0 is
considered to be less than the value +0.0. If both inputs are NaNs, the
result is the canonical NaN. If only one operand is a NaN, the result
is the non-NaN operand. Signaling NaN inputs set the invalid operation
exception flag, even when the result is not NaN."
Consequently for forwards compatibility with r20190608+ hardware we
cannot use the FMIN and FMAX machine instructions unconditionally even
where the ISA level of r2.2 has been specified with the `-misa-spec=2.2'
option where operation would be different between ISA revisions, that
is the handling of signaling NaN inputs.
Therefore provide new `fmin<mode>3' and `fmax<mode>3' patterns removing
the need to emit libcalls with the `__builtin_fmin' and `__builtin_fmax'
family of intrinsics, however limit them to where `-fno-signaling-nans'
is in effect, deferring to other code generation strategies otherwise as
applicable. Use newly-defined UNSPECs as the operation codes so that
the patterns are only ever used if referred to by their names, as there
is no RTL expression defined for the IEEE 754-2008 `minNum' and `maxNum'
operations.
References:
[1] "The RISC-V Instruction Set Manual, Volume I: User-Level ISA",
Document Version 2.2, May 7, 2017, Section 8.3 "NaN Generation and
Propagation", p. 48
[1] "The RISC-V Instruction Set Manual, Volume I: Unprivileged ISA",
Document Version 20190608-Base-Ratified, June 8, 2019, "Preface",
p. ii
[2] same, Section 11.6 "Single-Precision Floating-Point Computational
Instructions", p. 66
gcc/
* config/riscv/riscv.md (UNSPEC_FMIN, UNSPEC_FMAX): New
constants.
(fmin<mode>3, fmax<mode>3): New insns.
* testsuite/gcc.target/riscv/fmax-snan.c: New test.
* testsuite/gcc.target/riscv/fmax.c: New test.
* testsuite/gcc.target/riscv/fmaxf-snan.c: New test.
* testsuite/gcc.target/riscv/fmaxf.c: New test.
* testsuite/gcc.target/riscv/fmin-snan.c: New test.
* testsuite/gcc.target/riscv/fmin.c: New test.
* testsuite/gcc.target/riscv/fminf-snan.c: New test.
* testsuite/gcc.target/riscv/fminf.c: New test.
* testsuite/gcc.target/riscv/smax-ieee.c: New test.
* testsuite/gcc.target/riscv/smax.c: New test.
* testsuite/gcc.target/riscv/smaxf-ieee.c: New test.
* testsuite/gcc.target/riscv/smaxf.c: New test.
* testsuite/gcc.target/riscv/smin-ieee.c: New test.
* testsuite/gcc.target/riscv/smin.c: New test.
* testsuite/gcc.target/riscv/sminf-ieee.c: New test.
* testsuite/gcc.target/riscv/sminf.c: New test.
---
Hi,
I thought some test coverage would be good having in this area, so I have
added test cases for the new `fmin'/`fmax' and the existing `smin'/`smax'
patterns and in the course of making this improvement I have realised the
latter oned do actually have to be always available, and that using UNSPEC
operations will be more appropriate for the former ones, especially as the
respective RTL expressions previously used have non-IEEE semantics:
'(smin:M X Y)'
'(smax:M X Y)'
Represents the smaller (for 'smin') or larger (for 'smax') of X and
Y, interpreted as signed values in mode M. When used with floating
point, if both operands are zeros, or if either operand is 'NaN',
then it is unspecified which of the two operands is returned as the
result.
The new test cases assume the update I have recently submitted to make
use of the `gcc-dg-runtest' test driver will go ahead. They are trivial
to update otherwise (`-O2' would I guess be best used then).
I chose to further update the change description so as to refer to both
ISA revisions and "F"/"D" extension versions unambiguously.
This third version of the change has passed full GCC regression testing
with the `riscv64-linux-gnu' target using the HiFive Unmatched (U74 CPU)
target board.
Any further questions or comments? Otherwise OK once GCC 13 has opened?
Maciej
Changes from v2:
- Use UNSPECs for the `fmin'/`fmax' patterns, so that they cannot be
matched by the RTL expression.
- Revert the `HONOR_SNANS (<MODE>mode)' restriction for the `smin'/`smax'
patterns; it was wrong, because HONOR_SNANS implies HONOR_NANS, and that
is not true for `-ffinite-math-only' where `smin'/`smax' still have to
work.
- Add test cases.
- Further clarify ISA/extension revisions/versions.
Changes from v1:
- Adjust heading from "RISC-V: Replace `smin'/`smax' RTL patterns with
`fmin'/`fmax'".
- Do not remove `smin'/`smax' patterns; instead make them available if
`HONOR_SNANS (<MODE>mode)'.
- Make `fmin'/`fmax' patterns available if `!HONOR_SNANS (<MODE>mode)'
only.
- Update description accordingly; refer r2.2 and r20190608 ISA specs.
---
gcc/config/riscv/riscv.md | 22 ++++++++++++++++++++++
gcc/testsuite/gcc.target/riscv/fmax-snan.c | 12 ++++++++++++
gcc/testsuite/gcc.target/riscv/fmax.c | 12 ++++++++++++
gcc/testsuite/gcc.target/riscv/fmaxf-snan.c | 12 ++++++++++++
gcc/testsuite/gcc.target/riscv/fmaxf.c | 12 ++++++++++++
gcc/testsuite/gcc.target/riscv/fmin-snan.c | 12 ++++++++++++
gcc/testsuite/gcc.target/riscv/fmin.c | 12 ++++++++++++
gcc/testsuite/gcc.target/riscv/fminf-snan.c | 12 ++++++++++++
gcc/testsuite/gcc.target/riscv/fminf.c | 12 ++++++++++++
gcc/testsuite/gcc.target/riscv/smax-ieee.c | 12 ++++++++++++
gcc/testsuite/gcc.target/riscv/smax.c | 12 ++++++++++++
gcc/testsuite/gcc.target/riscv/smaxf-ieee.c | 12 ++++++++++++
gcc/testsuite/gcc.target/riscv/smaxf.c | 12 ++++++++++++
gcc/testsuite/gcc.target/riscv/smin-ieee.c | 12 ++++++++++++
gcc/testsuite/gcc.target/riscv/smin.c | 12 ++++++++++++
gcc/testsuite/gcc.target/riscv/sminf-ieee.c | 12 ++++++++++++
gcc/testsuite/gcc.target/riscv/sminf.c | 12 ++++++++++++
17 files changed, 214 insertions(+)
gcc-riscv-fmin-fmax.diff
Index: gcc/gcc/config/riscv/riscv.md
===================================================================
--- gcc.orig/gcc/config/riscv/riscv.md
+++ gcc/gcc/config/riscv/riscv.md
@@ -42,6 +42,8 @@
UNSPEC_COPYSIGN
UNSPEC_LRINT
UNSPEC_LROUND
+ UNSPEC_FMIN
+ UNSPEC_FMAX
;; Stack tie
UNSPEC_TIE
@@ -1216,6 +1218,26 @@
;;
;; ....................
+(define_insn "fmin<mode>3"
+ [(set (match_operand:ANYF 0 "register_operand" "=f")
+ (unspec:ANYF [(use (match_operand:ANYF 1 "register_operand" " f"))
+ (use (match_operand:ANYF 2 "register_operand" " f"))]
+ UNSPEC_FMIN))]
+ "TARGET_HARD_FLOAT && !HONOR_SNANS (<MODE>mode)"
+ "fmin.<fmt>\t%0,%1,%2"
+ [(set_attr "type" "fmove")
+ (set_attr "mode" "<UNITMODE>")])
+
+(define_insn "fmax<mode>3"
+ [(set (match_operand:ANYF 0 "register_operand" "=f")
+ (unspec:ANYF [(use (match_operand:ANYF 1 "register_operand" " f"))
+ (use (match_operand:ANYF 2 "register_operand" " f"))]
+ UNSPEC_FMAX))]
+ "TARGET_HARD_FLOAT && !HONOR_SNANS (<MODE>mode)"
+ "fmax.<fmt>\t%0,%1,%2"
+ [(set_attr "type" "fmove")
+ (set_attr "mode" "<UNITMODE>")])
+
(define_insn "smin<mode>3"
[(set (match_operand:ANYF 0 "register_operand" "=f")
(smin:ANYF (match_operand:ANYF 1 "register_operand" " f")
Index: gcc/gcc/testsuite/gcc.target/riscv/fmax-snan.c
===================================================================
--- /dev/null
+++ gcc/gcc/testsuite/gcc.target/riscv/fmax-snan.c
@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+/* { dg-options "-fno-finite-math-only -fsigned-zeros -fsignaling-nans -dp" }
*/
+
+double
+fmax (double x, double y)
+{
+ return __builtin_fmax (x, y);
+}
+
+/* { dg-final { scan-assembler-not "\tfmax\.d\t" } } */
+/* { dg-final { scan-assembler-not "\tfge\.d\t" } } */
+/* { dg-final { scan-assembler "\t(call|tail)\tfmax\t" } } */
Index: gcc/gcc/testsuite/gcc.target/riscv/fmax.c
===================================================================
--- /dev/null
+++ gcc/gcc/testsuite/gcc.target/riscv/fmax.c
@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+/* { dg-options "-fno-finite-math-only -fsigned-zeros -fno-signaling-nans -dp"
} */
+
+double
+fmax (double x, double y)
+{
+ return __builtin_fmax (x, y);
+}
+
+/* { dg-final { scan-assembler-not "\ttail\tfmax\t" } } */
+/* { dg-final { scan-assembler-not "\tfge\.d\t" } } */
+/* { dg-final { scan-assembler "\tfmax\.d\t\[^\n\]* fmaxdf3\n" } } */
Index: gcc/gcc/testsuite/gcc.target/riscv/fmaxf-snan.c
===================================================================
--- /dev/null
+++ gcc/gcc/testsuite/gcc.target/riscv/fmaxf-snan.c
@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+/* { dg-options "-fno-finite-math-only -fsigned-zeros -fsignaling-nans -dp" }
*/
+
+float
+fmaxf (float x, float y)
+{
+ return __builtin_fmaxf (x, y);
+}
+
+/* { dg-final { scan-assembler-not "\tfmax\.s\t" } } */
+/* { dg-final { scan-assembler-not "\tfge\.s\t" } } */
+/* { dg-final { scan-assembler "\t(call|tail)\tfmaxf\t" } } */
Index: gcc/gcc/testsuite/gcc.target/riscv/fmaxf.c
===================================================================
--- /dev/null
+++ gcc/gcc/testsuite/gcc.target/riscv/fmaxf.c
@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+/* { dg-options "-fno-finite-math-only -fsigned-zeros -fno-signaling-nans -dp"
} */
+
+float
+fmaxf (float x, float y)
+{
+ return __builtin_fmaxf (x, y);
+}
+
+/* { dg-final { scan-assembler-not "\ttail\tfmaxf\t" } } */
+/* { dg-final { scan-assembler-not "\tfge\.s\t" } } */
+/* { dg-final { scan-assembler "\tfmax\.s\t\[^\n\]* fmaxsf3\n" } } */
Index: gcc/gcc/testsuite/gcc.target/riscv/fmin-snan.c
===================================================================
--- /dev/null
+++ gcc/gcc/testsuite/gcc.target/riscv/fmin-snan.c
@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+/* { dg-options "-fno-finite-math-only -fsigned-zeros -fsignaling-nans -dp" }
*/
+
+double
+fmin (double x, double y)
+{
+ return __builtin_fmin (x, y);
+}
+
+/* { dg-final { scan-assembler-not "\tfmin\.d\t" } } */
+/* { dg-final { scan-assembler-not "\tfle\.d\t" } } */
+/* { dg-final { scan-assembler "\t(call|tail)\tfmin\t" } } */
Index: gcc/gcc/testsuite/gcc.target/riscv/fmin.c
===================================================================
--- /dev/null
+++ gcc/gcc/testsuite/gcc.target/riscv/fmin.c
@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+/* { dg-options "-fno-finite-math-only -fsigned-zeros -fno-signaling-nans -dp"
} */
+
+double
+fmin (double x, double y)
+{
+ return __builtin_fmin (x, y);
+}
+
+/* { dg-final { scan-assembler-not "\ttail\tfmin\t" } } */
+/* { dg-final { scan-assembler-not "\tfle\.d\t" } } */
+/* { dg-final { scan-assembler "\tfmin\.d\t\[^\n\]* fmindf3\n" } } */
Index: gcc/gcc/testsuite/gcc.target/riscv/fminf-snan.c
===================================================================
--- /dev/null
+++ gcc/gcc/testsuite/gcc.target/riscv/fminf-snan.c
@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+/* { dg-options "-fno-finite-math-only -fsigned-zeros -fsignaling-nans -dp" }
*/
+
+float
+fminf (float x, float y)
+{
+ return __builtin_fminf (x, y);
+}
+
+/* { dg-final { scan-assembler-not "\tfmin\.s\t" } } */
+/* { dg-final { scan-assembler-not "\tfle\.s\t" } } */
+/* { dg-final { scan-assembler "\t(call|tail)\tfminf\t" } } */
Index: gcc/gcc/testsuite/gcc.target/riscv/fminf.c
===================================================================
--- /dev/null
+++ gcc/gcc/testsuite/gcc.target/riscv/fminf.c
@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+/* { dg-options "-fno-finite-math-only -fsigned-zeros -fno-signaling-nans -dp"
} */
+
+float
+fminf (float x, float y)
+{
+ return __builtin_fminf (x, y);
+}
+
+/* { dg-final { scan-assembler-not "\ttail\tfminf\t" } } */
+/* { dg-final { scan-assembler-not "\tfle\.s\t" } } */
+/* { dg-final { scan-assembler "\tfmin\.s\t\[^\n\]* fminsf3\n" } } */
Index: gcc/gcc/testsuite/gcc.target/riscv/smax-ieee.c
===================================================================
--- /dev/null
+++ gcc/gcc/testsuite/gcc.target/riscv/smax-ieee.c
@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+/* { dg-options "-ffinite-math-only -fsigned-zeros -dp" } */
+
+double
+smax (double x, double y)
+{
+ return x >= y ? x : y;
+}
+
+/* { dg-final { scan-assembler-not "\t(call|tail)\tfmax\t" } } */
+/* { dg-final { scan-assembler-not "\tfmax\.d\t" } } */
+/* { dg-final { scan-assembler "\tfge\.d\t" } } */
Index: gcc/gcc/testsuite/gcc.target/riscv/smax.c
===================================================================
--- /dev/null
+++ gcc/gcc/testsuite/gcc.target/riscv/smax.c
@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+/* { dg-options "-ffinite-math-only -fno-signed-zeros -dp" } */
+
+double
+smax (double x, double y)
+{
+ return x >= y ? x : y;
+}
+
+/* { dg-final { scan-assembler-not "\ttail\tfmax\t" } } */
+/* { dg-final { scan-assembler-not "\tfge\.d\t" } } */
+/* { dg-final { scan-assembler "\tfmax\.d\t\[^\n\]* smaxdf3\n" } } */
Index: gcc/gcc/testsuite/gcc.target/riscv/smaxf-ieee.c
===================================================================
--- /dev/null
+++ gcc/gcc/testsuite/gcc.target/riscv/smaxf-ieee.c
@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+/* { dg-options "-ffinite-math-only -fsigned-zeros -dp" } */
+
+float
+smaxf (float x, float y)
+{
+ return x >= y ? x : y;
+}
+
+/* { dg-final { scan-assembler-not "\t(call|tail)\tfmaxf\t" } } */
+/* { dg-final { scan-assembler-not "\tfmax\.s\t" } } */
+/* { dg-final { scan-assembler "\tfge\.s\t" } } */
Index: gcc/gcc/testsuite/gcc.target/riscv/smaxf.c
===================================================================
--- /dev/null
+++ gcc/gcc/testsuite/gcc.target/riscv/smaxf.c
@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+/* { dg-options "-ffinite-math-only -fno-signed-zeros -dp" } */
+
+float
+smaxf (float x, float y)
+{
+ return x >= y ? x : y;
+}
+
+/* { dg-final { scan-assembler-not "\ttail\tfmaxf\t" } } */
+/* { dg-final { scan-assembler-not "\tfge\.s\t" } } */
+/* { dg-final { scan-assembler "\tfmax\.s\t\[^\n\]* smaxsf3\n" } } */
Index: gcc/gcc/testsuite/gcc.target/riscv/smin-ieee.c
===================================================================
--- /dev/null
+++ gcc/gcc/testsuite/gcc.target/riscv/smin-ieee.c
@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+/* { dg-options "-ffinite-math-only -fsigned-zeros -dp" } */
+
+double
+smin (double x, double y)
+{
+ return x <= y ? x : y;
+}
+
+/* { dg-final { scan-assembler-not "\t(call|tail)\tfmin\t" } } */
+/* { dg-final { scan-assembler-not "\tfmin\.d\t" } } */
+/* { dg-final { scan-assembler "\tfle\.d\t" } } */
Index: gcc/gcc/testsuite/gcc.target/riscv/smin.c
===================================================================
--- /dev/null
+++ gcc/gcc/testsuite/gcc.target/riscv/smin.c
@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+/* { dg-options "-ffinite-math-only -fno-signed-zeros -dp" } */
+
+double
+smin (double x, double y)
+{
+ return x <= y ? x : y;
+}
+
+/* { dg-final { scan-assembler-not "\ttail\tfmin\t" } } */
+/* { dg-final { scan-assembler-not "\tfle\.d\t" } } */
+/* { dg-final { scan-assembler "\tfmin\.d\t\[^\n\]* smindf3\n" } } */
Index: gcc/gcc/testsuite/gcc.target/riscv/sminf-ieee.c
===================================================================
--- /dev/null
+++ gcc/gcc/testsuite/gcc.target/riscv/sminf-ieee.c
@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+/* { dg-options "-ffinite-math-only -fsigned-zeros -dp" } */
+
+float
+sminf (float x, float y)
+{
+ return x <= y ? x : y;
+}
+
+/* { dg-final { scan-assembler-not "\t(call|tail)\tfminf\t" } } */
+/* { dg-final { scan-assembler-not "\tfmin\.s\t" } } */
+/* { dg-final { scan-assembler "\tfle\.s\t" } } */
Index: gcc/gcc/testsuite/gcc.target/riscv/sminf.c
===================================================================
--- /dev/null
+++ gcc/gcc/testsuite/gcc.target/riscv/sminf.c
@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+/* { dg-options "-ffinite-math-only -fno-signed-zeros -dp" } */
+
+float
+sminf (float x, float y)
+{
+ return x <= y ? x : y;
+}
+
+/* { dg-final { scan-assembler-not "\ttail\tfminf\t" } } */
+/* { dg-final { scan-assembler-not "\tfle\.s\t" } } */
+/* { dg-final { scan-assembler "\tfmin\.s\t\[^\n\]* sminsf3\n" } } */
