RISC-V: Fix weak symbols with medany and explicit relocs.

gcc/
	* config/riscv/riscv.c (riscv_split_symbol): Mark auipc label as weak
	when target symbol is weak.

	gcc/testsuite/
	* gcc.target/riscv/weak-1.c: New.

From-SVN: r264586

gcc/ChangeLog

@@ -1,3 +1,8 @@
+2018-09-25  Jim Wilson  <jimw@sifive.com>
+
+	* config/riscv/riscv.c (riscv_split_symbol): Mark auipc label as weak
+	when target symbol is weak.
+
 2018-09-25  Bernd Edlinger  <bernd.edlinger@hotmail.de>
 
 	PR c/87387

gcc/config/riscv/riscv.c

@@ -1103,6 +1103,11 @@ riscv_split_symbol (rtx temp, rtx addr, machine_mode mode, rtx *low_out)
 
 	  label = gen_rtx_SYMBOL_REF (Pmode, ggc_strdup (buf));
 	  SYMBOL_REF_FLAGS (label) |= SYMBOL_FLAG_LOCAL;
+	  /* ??? Ugly hack to make weak symbols work.  May need to change the
+	     RTL for the auipc and/or low patterns to get a better fix for
+	     this.  */
+	  if (! nonzero_address_p (addr))
+	    SYMBOL_REF_WEAK (label) = 1;
 
 	  if (temp == NULL)
 	    temp = gen_reg_rtx (Pmode);

gcc/testsuite/ChangeLog

@@ -1,3 +1,7 @@
+2018-09-25  Jim Wilson  <jimw@sifive.com>
+
+	* gcc.target/riscv/weak-1.c: New.
+
 2018-09-25  Jeff Law  <law@redhat.com>
 
 	* gcc.dg/warn-stpcpy-no-nul.c: Drop unnecessary xfails.

gcc/testsuite/gcc.target/riscv/weak-1.c

@@ -0,0 +1,14 @@
+/* { dg-do compile } */
+/* { dg-options "-mcmodel=medany -mexplicit-relocs -O" } */
+
+/* Verify that the branch doesn't get optimized away.  */
+extern int weak_func(void) __attribute__ ((weak));
+
+int
+sub (void)
+{
+  if (weak_func)
+    return weak_func ();
+  return 0;
+}
+/* { dg-final { scan-assembler "b\(ne|eq\)" } } */