https://gcc.gnu.org/g:fd042192094c456e275c53dfe92383bec1e9fca3
commit r16-1291-gfd042192094c456e275c53dfe92383bec1e9fca3
Author: Vineet Gupta <vine...@rivosinc.com>
Date: Sun Jun 8 14:55:11 2025 -0700
RISC-V: frm/mode-switch: robustify call_insn backtracking [PR120203]
As described in prior patches of this series, FRM mode switching state
machine has special handling around calls. After a call_insn, if in DYN_CALL
state, it needs to transition back to DYN, which requires back checking
if prev insn was indeed a call.
Defering/delaying this could lead to unncessary final transitions leading
to extraenous FRM save/restores.
However the current back checking of call_insn was too coarse-grained.
It used prev_nonnote_nondebug_insn_bb () which implies current insn to
be in the same BB as the call_insn, which need not always be true.
The problem is not with the API, but the use thereof.
Fix this by tracking call_insn more explicitly in TARGET_MODE_NEEDED.
- On seeing a call_insn, record a "call note".
- On subsequent insns if a "call note" is seen, do the needed state switch
and clear the note.
- Remove the old BB based search.
The number of FRM read/writes across SPEC2017 -Ofast -mrv64gcv improves.
Before After
------------- ---------------
frrm fsrmi fsrm frrm fsrmi frrm
perlbench_r 17 0 1 17 0 1
cpugcc_r 11 0 0 11 0 0
bwaves_r 16 0 1 16 0 1
mcf_r 11 0 0 11 0 0
cactusBSSN_r 19 0 1 19 0 1
namd_r 14 0 1 14 0 1
parest_r 24 0 1 24 0 1
povray_r 26 1 6 26 1 6
lbm_r 6 0 0 6 0 0
omnetpp_r 17 0 1 17 0 1
wrf_r 1268 13 1603 613 13 82
cpuxalan_r 17 0 1 17 0 1
ldecod_r 11 0 0 11 0 0
x264_r 11 0 0 11 0 0
blender_r 61 12 42 39 12 16
cam4_r 45 13 20 40 13 17
deepsjeng_r 11 0 0 11 0 0
imagick_r 132 16 25 33 16 18
leela_r 12 0 0 12 0 0
nab_r 13 0 1 13 0 1
exchange2_r 16 0 1 16 0 1
fotonik3d_r 19 0 1 19 0 1
roms_r 21 0 1 21 0 1
xz_r 6 0 0 6 0 0
----------------- --------------
1804 55 1707 1023 55 150
----------------- --------------
3566 1228
----------------- --------------
While this was a missed-optimization exercise, testing exposed a latent
bug as additional testsuite failure, captured as PR120203. The existing
test float-point-dynamic-frm-74.c was missing FRM save after a call
which this fixes (as a side-effect of robust call state tracking).
| frrm a5
| fsrmi 1
|
| vfadd.vv v1,v8,v9
| fsrm a5
| beq a1,zero,.L2
|
| call normalize_vl_1
| frrm a5
|
| .L3:
| fsrmi 3
| vfadd.vv v8,v8,v9
| fsrm a5
| jr ra
|
| .L2:
| call normalize_vl_2
| frrm a5 <-- missing
| j .L3
PR target/120203
gcc/ChangeLog:
* config/riscv/riscv.cc (CFUN_IN_CALL): New macro.
(struct mode_switching_info): Add new field.
(riscv_frm_adjust_mode_after_call): Remove.
(riscv_frm_mode_needed): Track call_insn.
gcc/testsuite/ChangeLog:
* gcc.target/riscv/rvv/base/float-point-dynamic-frm-74.c: Expect
an additional FRRM.
Signed-off-by: Vineet Gupta <vine...@rivosinc.com>
Diff:
---
gcc/config/riscv/riscv.cc | 42 +++++++++-------------
.../riscv/rvv/base/float-point-dynamic-frm-74.c | 2 +-
2 files changed, 17 insertions(+), 27 deletions(-)
diff --git a/gcc/config/riscv/riscv.cc b/gcc/config/riscv/riscv.cc
index 1e56ee5dcb63..3fd18c1646dc 100644
--- a/gcc/config/riscv/riscv.cc
+++ b/gcc/config/riscv/riscv.cc
@@ -107,6 +107,8 @@ along with GCC; see the file COPYING3. If not see
/* True the mode switching has static frm, or false. */
#define STATIC_FRM_P(c) ((c)->machine->mode_sw_info.static_frm_p)
+#define CFUN_IN_CALL(c) ((c)->machine->mode_sw_info.cfun_call)
+
/* True if we can use the instructions in the XTheadInt extension
to handle interrupts, or false. */
#define TH_INT_INTERRUPT(c) \
@@ -176,10 +178,13 @@ struct GTY(()) mode_switching_info {
mode instruction in the function or not. */
bool static_frm_p;
+ bool cfun_call;
+
mode_switching_info ()
{
dynamic_frm = NULL_RTX;
static_frm_p = false;
+ cfun_call = false;
}
};
@@ -12304,20 +12309,6 @@ riscv_emit_mode_set (int entity, int mode, int
prev_mode,
}
}
-/* Adjust the FRM_NONE insn after a call to FRM_DYN for the
- underlying emit. */
-
-static int
-riscv_frm_adjust_mode_after_call (rtx_insn *cur_insn, int mode)
-{
- rtx_insn *insn = prev_nonnote_nondebug_insn_bb (cur_insn);
-
- if (insn && CALL_P (insn))
- return riscv_vector::FRM_DYN;
-
- return mode;
-}
-
/* Return mode that frm must be switched into
prior to the execution of insn. */
@@ -12329,26 +12320,25 @@ riscv_frm_mode_needed (rtx_insn *cur_insn, int code)
/* The dynamic frm will be initialized only onece during cfun. */
DYNAMIC_FRM_RTL (cfun) = gen_reg_rtx (SImode);
emit_insn_at_entry (gen_frrmsi (DYNAMIC_FRM_RTL (cfun)));
+ CFUN_IN_CALL (cfun) = false;
}
if (CALL_P (cur_insn))
+ {
+ CFUN_IN_CALL (cfun) = true;
return riscv_vector::FRM_DYN_CALL;
+ }
int mode = code >= 0 ? get_attr_frm_mode (cur_insn) : riscv_vector::FRM_NONE;
if (mode == riscv_vector::FRM_NONE)
- /* After meet a call, we need to backup the frm because it may be
- updated during the call. Here, for each insn, we will check if
- the previous insn is a call or not. When previous insn is call,
- there will be 2 cases for the emit mode set.
-
- 1. Current insn is not MODE_NONE, then the mode switch framework
- will do the mode switch from MODE_CALL to MODE_NONE natively.
- 2. Current insn is MODE_NONE, we need to adjust the MODE_NONE to
- the MODE_DYN, and leave the mode switch itself to perform
- the emit mode set.
- */
- mode = riscv_frm_adjust_mode_after_call (cur_insn, mode);
+ {
+ if (CFUN_IN_CALL (cfun))
+ {
+ CFUN_IN_CALL (cfun) = false;
+ return riscv_vector::FRM_DYN;
+ }
+ }
return mode;
}
diff --git
a/gcc/testsuite/gcc.target/riscv/rvv/base/float-point-dynamic-frm-74.c
b/gcc/testsuite/gcc.target/riscv/rvv/base/float-point-dynamic-frm-74.c
index c8a580038ec9..15284828044d 100644
--- a/gcc/testsuite/gcc.target/riscv/rvv/base/float-point-dynamic-frm-74.c
+++ b/gcc/testsuite/gcc.target/riscv/rvv/base/float-point-dynamic-frm-74.c
@@ -33,7 +33,7 @@ test_float_point_dynamic_frm (vfloat32m1_t op1, vfloat32m1_t
op2,
}
/* { dg-final { scan-assembler-times
{vfadd\.v[vf]\s+v[0-9]+,\s*v[0-9]+,\s*[fav]+[0-9]+} 2 } } */
-/* { dg-final { scan-assembler-times {frrm\s+[axs][0-9]+} 2 } } */
+/* { dg-final { scan-assembler-times {frrm\s+[axs][0-9]+} 3 } } */
/* { dg-final { scan-assembler-times {fsrm\s+[axs][0-9]+} 2 } } */
/* { dg-final { scan-assembler-times {fsrmi\s+[01234]} 2 } } */
/* { dg-final { scan-assembler-not {fsrmi\s+[axs][0-9]+,\s*[01234]} } } */
