[gcc r15-10592] RISC-V: vsetvl: Add null check for fault-first loop [PR122652].

[Robin Dapp]

https://gcc.gnu.org/g:014dd4b845d97aa5823971ea8b58cf1811662554

commit r15-10592-g014dd4b845d97aa5823971ea8b58cf1811662554
Author: Robin Dapp <rdapp@ventanamicro.com>
Date:   Wed Nov 12 10:17:47 2025 +0100

    RISC-V: vsetvl: Add null check for fault-first loop [PR122652].
    
    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.
    
            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.
    
    (cherry picked from commit b2d0abfcd5a3a58e7967eb76bb3508e5ef20d9fa)

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

diff --git a/gcc/config/riscv/riscv-vsetvl.cc b/gcc/config/riscv/riscv-vsetvl.cc
index a8c92565541a..2f309b52183f 100644
--- a/gcc/config/riscv/riscv-vsetvl.cc
+++ b/gcc/config/riscv/riscv-vsetvl.cc
@@ -1178,7 +1178,7 @@ 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 000000000000..bd8f1b4d3ef2
--- /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);
+  }
+}