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 <vineetg@rivosinc.com>

diff --git a/gcc/config/riscv/riscv.cc b/gcc/config/riscv/riscv.cc
index 1e56ee5dcb63e8c18de9116f926da39a26d7ce11..3fd18c1646dcab505d14f6de0cf83f2cb227dacd 100644 (file)
--- 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 c8a580038ec9f879e37c2449ff9faf6f09b19930..15284828044daa746c0bf04419b5c08873343270 100644 (file)
--- 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]} } } */