[HSA] Avoid ICE when "HSA does not implement indirect calls"

Made apparent by recent commit dc70315
"openmp: Implement discovery of implicit declare target to clauses":

    +FAIL: libgomp.c/target-39.c (internal compiler error)
    +FAIL: libgomp.c/target-39.c (test for excess errors)
    +UNRESOLVED: libgomp.c/target-39.c compilation failed to produce executable

This is in a '--enable-offload-targets=[...],hsa' build, with '-foffload=hsa'
enabled (by default).

    during GIMPLE pass: hsagen
    source-gcc/libgomp/testsuite/libgomp.c/target-39.c: In function ‘main._omp_fn.0.hsa.0’:
    source-gcc/libgomp/testsuite/libgomp.c/target-39.c:23:11: internal compiler error: Segmentation fault
       23 |   #pragma omp target map(from:err)
          |           ^~~
    [...]

GDB:

    Program received signal SIGSEGV, Segmentation fault.
    fndecl_built_in_p (node=0x0, name=BUILT_IN_PREFETCH) at [...]/source-gcc/gcc/tree.h:6267
    6267      return (fndecl_built_in_p (node, BUILT_IN_NORMAL)
    (gdb) bt
    #0  fndecl_built_in_p (node=0x0, name=BUILT_IN_PREFETCH) at [...]/source-gcc/gcc/tree.h:6267
    #1  0x0000000000b19739 in gen_hsa_insns_for_call (stmt=stmt@entry=0x7ffff693b200, hbb=hbb@entry=0x2b152c0) at [...]/source-gcc/gcc/hsa-gen.c:5304
    gcc-mirror#2  0x0000000000b1aca7 in gen_hsa_insns_for_gimple_stmt (stmt=0x7ffff693b200, hbb=hbb@entry=0x2b152c0) at [...]/source-gcc/gcc/hsa-gen.c:5770
    gcc-mirror#3  0x0000000000b1bd21 in gen_body_from_gimple () at [...]/source-gcc/gcc/hsa-gen.c:5999
    gcc-mirror#4  0x0000000000b1dbd2 in generate_hsa (kernel=<optimized out>) at [...]/source-gcc/gcc/hsa-gen.c:6596
    gcc-mirror#5  0x0000000000b1de66 in (anonymous namespace)::pass_gen_hsail::execute (this=0x2a2aac0) at [...]/source-gcc/gcc/hsa-gen.c:6680
    gcc-mirror#6  0x0000000000d06f90 in execute_one_pass (pass=pass@entry=0x2a2aac0) at [...]/source-gcc/gcc/passes.c:2502
    [...]
    (gdb) up
    #1  0x0000000000b19739 in gen_hsa_insns_for_call (stmt=stmt@entry=0x7ffff693b200, hbb=hbb@entry=0x2b152c0) at /home/thomas/tmp/source/gcc/build/track-slim-omp/source-gcc/gcc/hsa-gen.c:5304
    5304          if (fndecl_built_in_p (function_decl, BUILT_IN_PREFETCH))
    (gdb) print function_decl
    $1 = (tree) 0x0
    (gdb) list
    5299      if (!gimple_call_builtin_p (stmt, BUILT_IN_NORMAL))
    5300        {
    5301          tree function_decl = gimple_call_fndecl (stmt);
    5302          /* Prefetch pass can create type-mismatching prefetch builtin calls which
    5303             fail the gimple_call_builtin_p test above.  Handle them here.  */
    5304          if (fndecl_built_in_p (function_decl, BUILT_IN_PREFETCH))
    5305            return;
    5306
    5307          if (function_decl == NULL_TREE)
    5308            {

The problem is present already since 2016-11-23 commit
56b1c60 (r242761) "Merge from HSA branch to
trunk", and the fix obvious enough.

	gcc/
	* hsa-gen.c (gen_hsa_insns_for_call): Move 'function_decl ==
	NULL_TREE' check earlier.
	gcc/testsuite/
	* c-c++-common/gomp/hsa-indirect-call-1.c: New file.

(cherry picked from commit 973bce0)

gcc/hsa-gen.c

@@ -5299,10 +5299,6 @@ gen_hsa_insns_for_call (gimple *stmt, hsa_bb *hbb)
   if (!gimple_call_builtin_p (stmt, BUILT_IN_NORMAL))
     {
       tree function_decl = gimple_call_fndecl (stmt);
-      /* Prefetch pass can create type-mismatching prefetch builtin calls which
-	 fail the gimple_call_builtin_p test above.  Handle them here.  */
-      if (fndecl_built_in_p (function_decl, BUILT_IN_PREFETCH))
-	return;
 
       if (function_decl == NULL_TREE)
 	{
@@ -5311,6 +5307,11 @@ gen_hsa_insns_for_call (gimple *stmt, hsa_bb *hbb)
 	  return;
 	}
 
+      /* Prefetch pass can create type-mismatching prefetch builtin calls which
+	 fail the gimple_call_builtin_p test above.  Handle them here.  */
+      if (fndecl_built_in_p (function_decl, BUILT_IN_PREFETCH))
+	return;
+
       if (hsa_callable_function_p (function_decl))
 	gen_hsa_insns_for_direct_call (stmt, hbb);
       else if (!gen_hsa_insns_for_known_library_call (stmt, hbb))

gcc/testsuite/c-c++-common/gomp/hsa-indirect-call-1.c

@@ -0,0 +1,24 @@
+/* Instead of ICE, we'd like "HSA does not implement indirect calls".  */
+
+/* Reduced from 'libgomp.c/target-39.c'.  */
+
+/* { dg-require-effective-target offload_hsa } */
+/* { dg-additional-options "-Whsa" } to override '{gcc,g++}.dg/gomp/gomp.exp'.  */
+
+typedef void (*fnp) (void);
+void f1 (void) { }
+fnp f2 (void) { return f1; }
+#pragma omp declare target to (f1, f2)
+
+int
+main ()
+{
+  #pragma omp target
+  {
+    fnp fnp = f2 ();
+    fnp (); /* { dg-message "note: support for HSA does not implement indirect calls" } */
+  }
+  return 0;
+}
+
+/* { dg-warning "could not emit HSAIL for the function" "" { target *-*-* } 0 } */