[Committed V2] RISC-V: Fix VSETVL PASS bug

[Committed V2] RISC-V: Fix VSETVL PASS bug

[Juzhe-Zhong]

As PR112855 mentioned, the VSETVL PASS insert vsetvli in unexpected location.

Due to 2 reasons:
1. incorrect transparant computation LCM data. We need to check VL operand defs and uses.
2. incorrect fusion of unrelated edge which is the edge never reach the vsetvl expression.

	PR target/112855

gcc/ChangeLog:

	* config/riscv/riscv-vsetvl.cc (pre_vsetvl::compute_lcm_local_properties): Fix transparant LCM data.
	(pre_vsetvl::earliest_fuse_vsetvl_info): Disable earliest fusion for unrelated edge.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/autovec/pr112855.c: New test.

---
 gcc/config/riscv/riscv-vsetvl.cc              | 66 ++++++++++++++++++-
 .../gcc.target/riscv/rvv/autovec/pr112855.c   | 26 ++++++++
 2 files changed, 89 insertions(+), 3 deletions(-)
 create mode 100644 gcc/testsuite/gcc.target/riscv/rvv/autovec/pr112855.c

diff --git a/gcc/config/riscv/riscv-vsetvl.cc b/gcc/config/riscv/riscv-vsetvl.cc
index 484a8b3a514..68f0be7e81d 100644
--- a/gcc/config/riscv/riscv-vsetvl.cc
+++ b/gcc/config/riscv/riscv-vsetvl.cc
@@ -2034,7 +2034,7 @@ private:
     gcc_unreachable ();
   }
 
-  bool anticpatable_exp_p (const vsetvl_info &header_info)
+  bool anticipated_exp_p (const vsetvl_info &header_info)
   {
     if (!header_info.has_nonvlmax_reg_avl () && !header_info.has_vl ())
       return true;
@@ -2645,7 +2645,7 @@ pre_vsetvl::compute_lcm_local_properties ()
 		    }
 		}
 
-	      for (const insn_info *insn : bb->real_nondebug_insns ())
+	      for (insn_info *insn : bb->real_nondebug_insns ())
 		{
 		  if (info.has_nonvlmax_reg_avl ()
 		      && find_access (insn->defs (), REGNO (info.get_avl ())))
@@ -2653,6 +2653,59 @@ pre_vsetvl::compute_lcm_local_properties ()
 		      bitmap_clear_bit (m_transp[bb_index], i);
 		      break;
 		    }
+
+		  if (info.has_vl ()
+		      && reg_mentioned_p (info.get_vl (), insn->rtl ()))
+		    {
+		      if (find_access (insn->defs (), REGNO (info.get_vl ())))
+			/* We can't fuse vsetvl into the blocks that modify the
+			   VL operand since successors of such blocks will need
+			   the value of those blocks are defining.
+
+					  bb 4: def a5
+					  /   \
+				  bb 5:use a5  bb 6:vsetvl a5, 5
+
+			   The example above shows that we can't fuse vsetvl
+			   from bb 6 into bb 4 since the successor bb 5 is using
+			   the value defined in bb 4.  */
+			;
+		      else
+			{
+			  /* We can't fuse vsetvl into the blocks that use the
+			     VL operand which has different value from the
+			     vsetvl info.
+
+					    bb 4: def a5
+					      |
+					    bb 5: use a5
+					      |
+					    bb 6: def a5
+					      |
+					    bb 7: use a5
+
+			     The example above shows that we can't fuse vsetvl
+			     from bb 6 into bb 5 since their value is different.
+			   */
+			  resource_info resource
+			    = full_register (REGNO (info.get_vl ()));
+			  def_lookup dl = crtl->ssa->find_def (resource, insn);
+			  def_info *def
+			    = dl.matching_set_or_last_def_of_prev_group ();
+			  gcc_assert (def);
+			  insn_info *def_insn = extract_single_source (
+			    dyn_cast<set_info *> (def));
+			  if (def_insn && vsetvl_insn_p (def_insn->rtl ()))
+			    {
+			      vsetvl_info def_info = vsetvl_info (def_insn);
+			      if (m_dem.compatible_p (def_info, info))
+				continue;
+			    }
+			}
+
+		      bitmap_clear_bit (m_transp[bb_index], i);
+		      break;
+		    }
 		}
 	    }
 
@@ -2663,7 +2716,7 @@ pre_vsetvl::compute_lcm_local_properties ()
       vsetvl_info &footer_info = block_info.get_exit_info ();
 
       if (header_info.valid_p ()
-	  && (anticpatable_exp_p (header_info) || block_info.full_available))
+	  && (anticipated_exp_p (header_info) || block_info.full_available))
 	bitmap_set_bit (m_antloc[bb_index],
 			get_expr_index (m_exprs, header_info));
 
@@ -2920,6 +2973,13 @@ pre_vsetvl::earliest_fuse_vsetvl_info ()
 	      || eg->dest == EXIT_BLOCK_PTR_FOR_FN (cfun))
 	    continue;
 
+	  /* When multiple set bits in earliest edge, such edge may
+	     have infinite loop in preds or succs or multiple conflict
+	     vsetvl expression which make such edge is unrelated.  We
+	     don't perform fusion for such situation.  */
+	  if (bitmap_count_bits (e) != 1)
+	    continue;
+
 	  vsetvl_block_info &src_block_info = get_block_info (eg->src);
 	  vsetvl_block_info &dest_block_info = get_block_info (eg->dest);
 
diff --git a/gcc/testsuite/gcc.target/riscv/rvv/autovec/pr112855.c b/gcc/testsuite/gcc.target/riscv/rvv/autovec/pr112855.c
new file mode 100644
index 00000000000..f1fa6693d2d
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/rvv/autovec/pr112855.c
@@ -0,0 +1,26 @@
+/* { dg-do run } */
+/* { dg-options "-O3" } */
+/* { dg-require-effective-target rv64 } */
+/* { dg-require-effective-target riscv_v } */
+
+#include <assert.h>
+int a;
+int b = 100;
+int c[25];
+int d;
+int main() {
+  int e;
+  d = 0;
+  for (; d < 5; d++) {
+    e = 0;
+    for (; e < 5; e++)
+      c[d * 5 + e] = 0;
+  }
+  if (b)
+    if (a)
+      for (;;)
+        ;
+  b++;
+  int volatile f = *c;
+  assert(b == 101);
+}
-- 
2.36.3

Re: [Committed V2] RISC-V: Fix VSETVL PASS bug

[Patrick O'Neill]

Hi Juzhe,

An assert added in this patch is firing on a testcase on rv64gcv:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112888

Thanks,
Patrick

On 12/6/23 06:26, Juzhe-Zhong wrote:
> As PR112855 mentioned, the VSETVL PASS insert vsetvli in unexpected location.
>
> Due to 2 reasons:
> 1. incorrect transparant computation LCM data. We need to check VL operand defs and uses.
> 2. incorrect fusion of unrelated edge which is the edge never reach the vsetvl expression.
>
> 	PR target/112855
>
> gcc/ChangeLog:
>
> 	* config/riscv/riscv-vsetvl.cc (pre_vsetvl::compute_lcm_local_properties): Fix transparant LCM data.
> 	(pre_vsetvl::earliest_fuse_vsetvl_info): Disable earliest fusion for unrelated edge.
>
> gcc/testsuite/ChangeLog:
>
> 	* gcc.target/riscv/rvv/autovec/pr112855.c: New test.