RISC-V: Suppress the vsetvl fusion for conflict successors

Update in v2: Add dump information.

This patch fixes the following ineffective vsetvl insertion:

void f (int32_t * restrict in, int32_t * restrict out, size_t n, size_t cond, size_t cond2)
{
  for (size_t i = 0; i < n; i++)
    {
      if (i == cond) {
        vint8mf8_t v = *(vint8mf8_t*)(in + i + 100);
        *(vint8mf8_t*)(out + i + 100) = v;
      } else if (i == cond2) {
        vfloat32mf2_t v = *(vfloat32mf2_t*)(in + i + 200);
        *(vfloat32mf2_t*)(out + i + 200) = v;
      } else if (i == (cond2 - 1)) {
        vuint16mf2_t v = *(vuint16mf2_t*)(in + i + 300);
        *(vuint16mf2_t*)(out + i + 300) = v;
      } else {
        vint8mf4_t v = *(vint8mf4_t*)(in + i + 400);
        *(vint8mf4_t*)(out + i + 400) = v;
      }
    }
}

Before this patch:

f:
.LFB0:
        .cfi_startproc
        beq     a2,zero,.L12
        addi    a7,a0,400
        addi    a6,a1,400
        addi    a0,a0,1600
        addi    a1,a1,1600
        li      a5,0
        addi    t6,a4,-1
        vsetvli t3,zero,e8,mf8,ta,ma     ---> ineffective uplift
.L7:
        beq     a3,a5,.L15
        beq     a4,a5,.L16
        beq     t6,a5,.L17
        vsetvli t1,zero,e8,mf4,ta,ma
        vle8.v  v1,0(a0)
        vse8.v  v1,0(a1)
        vsetvli t3,zero,e8,mf8,ta,ma
.L4:
        addi    a5,a5,1
        addi    a7,a7,4
        addi    a6,a6,4
        addi    a0,a0,4
        addi    a1,a1,4
        bne     a2,a5,.L7
.L12:
        ret
.L15:
        vle8.v  v1,0(a7)
        vse8.v  v1,0(a6)
        j       .L4
.L17:
        vsetvli t1,zero,e8,mf4,ta,ma
        addi    t5,a0,-400
        addi    t4,a1,-400
        vle16.v v1,0(t5)
        vse16.v v1,0(t4)
        vsetvli t3,zero,e8,mf8,ta,ma
        j       .L4
.L16:
        addi    t5,a0,-800
        addi    t4,a1,-800
        vle32.v v1,0(t5)
        vse32.v v1,0(t4)
        j       .L4

It's obvious that we are hoisting the e8mf8 vsetvl to the top. It's ineffective since e8mf8 comes from
low probability block which is if (i == cond).

For this case, we disable such fusion.

After this patch:

f:
	beq	a2,zero,.L12
	addi	a7,a0,400
	addi	a6,a1,400
	addi	a0,a0,1600
	addi	a1,a1,1600
	li	a5,0
	addi	t6,a4,-1
.L7:
	beq	a3,a5,.L15
	beq	a4,a5,.L16
	beq	t6,a5,.L17
	vsetvli	t1,zero,e8,mf4,ta,ma
	vle8.v	v1,0(a0)
	vse8.v	v1,0(a1)
.L4:
	addi	a5,a5,1
	addi	a7,a7,4
	addi	a6,a6,4
	addi	a0,a0,4
	addi	a1,a1,4
	bne	a2,a5,.L7
.L12:
	ret
.L15:
	vsetvli	t3,zero,e8,mf8,ta,ma
	vle8.v	v1,0(a7)
	vse8.v	v1,0(a6)
	j	.L4
.L17:
	addi	t5,a0,-400
	addi	t4,a1,-400
	vsetvli	t1,zero,e8,mf4,ta,ma
	vle16.v	v1,0(t5)
	vse16.v	v1,0(t4)
	j	.L4
.L16:
	addi	t5,a0,-800
	addi	t4,a1,-800
	vsetvli	t3,zero,e32,mf2,ta,ma
	vle32.v	v1,0(t5)
	vse32.v	v1,0(t4)
	j	.L4

Tested on both RV32/RV64 no regression. Ok for trunk ?

	PR target/113696

gcc/ChangeLog:

	* config/riscv/riscv-vsetvl.cc (pre_vsetvl::earliest_fuse_vsetvl_info):
	Suppress vsetvl fusion.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/vsetvl/pr113696.c: New test.

2 files changed, 51 insertions, 0 deletions

diff --git a/gcc/config/riscv/riscv-vsetvl.cc b/gcc/config/riscv/riscv-vsetvl.cc
index 32f262d..48ce757 100644
--- a/gcc/config/riscv/riscv-vsetvl.cc
+++ b/gcc/config/riscv/riscv-vsetvl.cc
@@ -3001,6 +3001,31 @@ pre_vsetvl::earliest_fuse_vsetvl_info (int iter)
 		      src_block_info.set_empty_info ();
 		      src_block_info.probability
 			= profile_probability::uninitialized ();
+		      /* See PR113696, we should reset immediate dominator to
+			 empty since we may uplift ineffective vsetvl which
+			 locate at low probability block.  */
+		      basic_block dom
+			= get_immediate_dominator (CDI_DOMINATORS, eg->src);
+		      auto &dom_block_info = get_block_info (dom);
+		      if (dom_block_info.has_info ()
+			  && !m_dem.compatible_p (
+			    dom_block_info.get_exit_info (), curr_info))
+			{
+			  dom_block_info.set_empty_info ();
+			  dom_block_info.probability
+			    = profile_probability::uninitialized ();
+			  if (dump_file && (dump_flags & TDF_DETAILS))
+			    {
+			      fprintf (dump_file,
+				       "      Reset dominator bb %u:",
+				       dom->index);
+			      prev_info.dump (dump_file, "        ");
+			      fprintf (dump_file,
+				       "	due to (same probability or no "
+				       "compatible reaching):");
+			      curr_info.dump (dump_file, "        ");
+			    }
+			}
 		      changed = true;
 		    }
 		  /* Choose the one with higher probability. */
diff --git a/gcc/testsuite/gcc.target/riscv/rvv/vsetvl/pr113696.c b/gcc/testsuite/gcc.target/riscv/rvv/vsetvl/pr113696.c
new file mode 100644
index 0000000..5d7c5f5
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/rvv/vsetvl/pr113696.c
@@ -0,0 +1,26 @@
+/* { dg-do compile } */
+/* { dg-options "--param=riscv-autovec-preference=scalable -march=rv64gcv -mabi=lp64d -O3" } */
+
+#include "riscv_vector.h"
+
+void f (int32_t * restrict in, int32_t * restrict out, size_t n, size_t cond, size_t cond2)
+{
+  for (size_t i = 0; i < n; i++)
+    {
+      if (i == cond) {
+        vint8mf8_t v = *(vint8mf8_t*)(in + i + 100);
+        *(vint8mf8_t*)(out + i + 100) = v;
+      } else if (i == cond2) {
+        vfloat32mf2_t v = *(vfloat32mf2_t*)(in + i + 200);
+        *(vfloat32mf2_t*)(out + i + 200) = v;
+      } else if (i == (cond2 - 1)) {
+        vuint16mf2_t v = *(vuint16mf2_t*)(in + i + 300);
+        *(vuint16mf2_t*)(out + i + 300) = v;
+      } else {
+        vint8mf4_t v = *(vint8mf4_t*)(in + i + 400);
+        *(vint8mf4_t*)(out + i + 400) = v;
+      }
+    }
+}
+
+/* { dg-final { scan-assembler-times {vsetvli} 4 { target { no-opts "-O0"  no-opts "-Os" no-opts "-Oz" no-opts "-funroll-loops" no-opts "-g" } } } } */