[PATCH v2 1/2] aarch64: Don't return invalid GIMPLE assign statements

[Andrew Carlotti <andrew.carlotti@arm.com>]

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 --git a/gcc/config/aarch64/aarch64-builtins.cc b/gcc/config/aarch64/aarch64-builtins.cc
index e0a741ac663188713e21f457affa57217d074783..5753988a9964967c27a03aca5fddb9025fd8ed6e 100644
--- a/gcc/config/aarch64/aarch64-builtins.cc
+++ b/gcc/config/aarch64/aarch64-builtins.cc
@@ -3022,6 +3022,16 @@ 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 0000000000000000000000000000000000000000..345307456b175307f5cb22de5e59cfc6254f2737
--- /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());
+}