[PATCH 2/2] RISC-V: Allow uninitialized preferred_else_value for RVV

[YunQiang Su]

From: YunQiang Su <yunqi...@isrc.iscas.ac.cn>

PR target/115840.

In riscv_preferred_else_value, we create an uninitialized tmp var
for else value, instead of the 0 (as default_preferred_else_value)
or the pre-exists VAR (as aarch64 does), so that we can use agnostic
policy.

The problem is that `warn_uninit` will emit a warning:
  ({anonymous})’ may be used uninitialized

Let's mark this tmp var as "allow_uninitialized".

This problem is found when I try to build glibc with V extension.

gcc
        PR target/115840.
        * config/riscv/riscv.cc(riscv_preferred_else_value): Mark
        tmp_var as allow_unitialized.

gcc/testsuite
        * gcc.dg/vect/pr115840.c: New testcase.
---
 gcc/config/riscv/riscv.cc            |  6 +++++-
 gcc/testsuite/gcc.dg/vect/pr115840.c | 11 +++++++++++
 2 files changed, 16 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/gcc.dg/vect/pr115840.c

diff --git a/gcc/config/riscv/riscv.cc b/gcc/config/riscv/riscv.cc
index 61fa74e9322..08159d7cbbc 100644
--- a/gcc/config/riscv/riscv.cc
+++ b/gcc/config/riscv/riscv.cc
@@ -11431,7 +11431,11 @@ riscv_preferred_else_value (unsigned ifn, tree 
vectype, unsigned int nops,
                            tree *ops)
 {
   if (riscv_v_ext_mode_p (TYPE_MODE (vectype)))
-    return get_or_create_ssa_default_def (cfun, create_tmp_var (vectype));
+    {
+      tree tmp_var = create_tmp_var (vectype);
+      TREE_ALLOW_UNINITIALIZED (tmp_var) = 1;
+      return get_or_create_ssa_default_def (cfun, tmp_var);
+    }
 
   return default_preferred_else_value (ifn, vectype, nops, ops);
 }
diff --git a/gcc/testsuite/gcc.dg/vect/pr115840.c 
b/gcc/testsuite/gcc.dg/vect/pr115840.c
new file mode 100644
index 00000000000..09dc9e4eb7c
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/pr115840.c
@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+/* { dg-additional-options "-Wall -Werror" } */
+
+double loads[16];
+
+void
+foo (double loadavg[], int count)
+{
+  for (int i = 0; i < count; i++)
+    loadavg[i] = loads[i] / 1.5;
+}
-- 
2.45.1