[PATCH] RISC-V: vsetvl: Add null check for fault-first loop [PR122652].

[Robin Dapp]

Hi,

For a fault-first load we store the first instruction that read its VL
result.  The loop to do so uses next_nondebug_insn () which returns
nullptr when we are at the end.  Check for that before accessing the
next insn.

Regtested on rv64gcbv_zvl512b, going to commit if the CI is clean.

Regards
 Robin

        PR target/122652

gcc/ChangeLog:

        * config/riscv/riscv-vsetvl.cc: Add nullptr check.

gcc/testsuite/ChangeLog:

        * gcc.target/riscv/rvv/base/pr122652.c: New test.
---
 gcc/config/riscv/riscv-vsetvl.cc              |  2 +-
 .../gcc.target/riscv/rvv/base/pr122652.c      | 22 +++++++++++++++++++
 2 files changed, 23 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/gcc.target/riscv/rvv/base/pr122652.c

diff --git a/gcc/config/riscv/riscv-vsetvl.cc b/gcc/config/riscv/riscv-vsetvl.cc
index 580ac9cbe8e..127187b4555 100644
--- a/gcc/config/riscv/riscv-vsetvl.cc
+++ b/gcc/config/riscv/riscv-vsetvl.cc
@@ -1176,7 +1176,7 @@ public:
     if (fault_first_load_p (insn->rtl ()))
       {
        for (insn_info *i = insn->next_nondebug_insn ();
-            i->bb () == insn->bb (); i = i->next_nondebug_insn ())
+            i && i->bb () == insn->bb (); i = i->next_nondebug_insn ())
          {
            if (find_access (i->defs (), VL_REGNUM))
              break;
diff --git a/gcc/testsuite/gcc.target/riscv/rvv/base/pr122652.c 
b/gcc/testsuite/gcc.target/riscv/rvv/base/pr122652.c
new file mode 100644
index 00000000000..bd8f1b4d3ef
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/rvv/base/pr122652.c
@@ -0,0 +1,22 @@
+/* { dg-do compile } */
+/* { dg-options "-O3 -march=rv64gcv -mabi=lp64d" } */
+
+#include "riscv_vector.h"
+
+int a;
+int b();
+
+int c() {
+  if (b())
+    a = 0;
+}
+
+void d() {
+  for (; c() + d;) {
+    long e, h;
+    char *f;
+    __rvv_uint16mf4_t g;
+    __rvv_uint8mf8x3_t i = __riscv_vlseg3e8ff_v_u8mf8x3(f, &h, e);
+    __riscv_vsoxseg3ei16_v_u8mf8x3(0, g, i, 0);
+  }
+}
-- 
2.51.1