[gcc r13-1654] aarch64: Don't return invalid GIMPLE assign statements

[Richard Sandiford <rsandifo@gcc.gnu.org>]

https://gcc.gnu.org/g:e9cad1e582950d129aba3465b65c2231f94bb6c0

commit r13-1654-ge9cad1e582950d129aba3465b65c2231f94bb6c0
Author: Andrew Carlotti <andrew.carlotti@arm.com>
Date:   Wed Jul 13 09:01:51 2022 +0100

    aarch64: Don't return invalid GIMPLE assign statements
    
    aarch64_general_gimple_fold_builtin doesn't check whether the LHS of a
    function call is null before converting it to an assign statement. To avoid
    returning an invalid GIMPLE statement in this case, we instead assign the
    expression result to a new (unused) variable.
    
    This change only affects code that:
    1) Calls an intrinsic function that has no side effects;
    2) Does not use or store the value returned by the intrinsic;
    3) Uses parameters that prevent the front-end eliminating the call prior to
    gimplification.
    
    The ICE is unlikely to have occurred in the wild, as it relies on the presence
    of a redundant intrinsic call.
    
    gcc/ChangeLog:
    
            * config/aarch64/aarch64-builtins.cc
            (aarch64_general_gimple_fold_builtin): Add fixup for invalid GIMPLE.
    
    gcc/testsuite/ChangeLog:
    
            * gcc.target/aarch64/advsimd-intrinsics/ignored_return_1.c: New test.

Diff:
---
 gcc/config/aarch64/aarch64-builtins.cc                         | 10 ++++++++++
 .../gcc.target/aarch64/advsimd-intrinsics/ignored_return_1.c   |  9 +++++++++
 2 files changed, 19 insertions(+)

diff --git a/gcc/config/aarch64/aarch64-builtins.cc b/gcc/config/aarch64/aarch64-builtins.cc
index adfddb8b215..4621c6d43da 100644
--- a/gcc/config/aarch64/aarch64-builtins.cc
+++ b/gcc/config/aarch64/aarch64-builtins.cc
@@ -2907,6 +2907,16 @@ aarch64_general_gimple_fold_builtin (unsigned int fcode, gcall *stmt,
     default:
       break;
     }
+
+  /* GIMPLE assign statements (unlike calls) require a non-null lhs. If we
+     created an assign statement with a null lhs, then fix this by assigning
+     to a new (and subsequently unused) variable. */
+  if (new_stmt && is_gimple_assign (new_stmt) && !gimple_assign_lhs (new_stmt))
+    {
+      tree new_lhs = make_ssa_name (gimple_call_return_type (stmt));
+      gimple_assign_set_lhs (new_stmt, new_lhs);
+    }
+
   return new_stmt;
 }
 
diff --git a/gcc/testsuite/gcc.target/aarch64/advsimd-intrinsics/ignored_return_1.c b/gcc/testsuite/gcc.target/aarch64/advsimd-intrinsics/ignored_return_1.c
new file mode 100644
index 00000000000..345307456b1
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/advsimd-intrinsics/ignored_return_1.c
@@ -0,0 +1,9 @@
+/* { dg-do compile { target { aarch64*-*-* } } } */
+
+#include <arm_neon.h>
+
+int8_t *bar();
+
+void foo() {
+  __builtin_aarch64_ld1v16qi(bar());
+}