2015-06-04 Sriraman Tallam <tmsriram@google.com>

	* c-family/c-common.c (noplt): New attribute.
	(handle_noplt_attribute): New handler.
	* calls.c (prepare_call_address): Check for noplt
	attribute.
	* config/i386/i386.c (ix86_expand_call): Check
	for noplt attribute.
	(ix86_nopic_noplt_attribute_p): New function.
	(ix86_output_call_insn): Output indirect call for non-pic
	no plt calls.
	* doc/extend.texi (noplt): Document new attribute.
	* doc/invoke.texi: Document new attribute.
	* testsuite/gcc.target/i386/noplt-1.c: New test.
	* testsuite/gcc.target/i386/noplt-2.c: New test.
	* testsuite/gcc.target/i386/noplt-3.c: New test.
	* testsuite/gcc.target/i386/noplt-4.c: New test.

This patch does two things:

* Adds new generic function attribute "noplt" that is similar in functionality
  to -fno-plt except that it applies only to calls to functions that are marked
  with this attribute.
* For x86_64, it makes -fno-plt(and the attribute) also work for non-PIC code by
  directly generating an indirect call via a GOT entry.



git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@224138 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 39 insertions, 4 deletions

diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
index 8aa4fdbd70c..153dd85babf 100644
--- a/gcc/config/i386/i386.c
+++ b/gcc/config/i386/i386.c
@@ -25495,13 +25495,19 @@ ix86_expand_call (rtx retval, rtx fnaddr, rtx callarg1,
     }
   else
     {
-      /* Static functions and indirect calls don't need the pic register.  */
+      /* Static functions and indirect calls don't need the pic register.  Also,
+	 check if PLT was explicitly avoided via no-plt or "noplt" attribute, making
+	 it an indirect call.  */
       if (flag_pic
 	  && (!TARGET_64BIT
 	      || (ix86_cmodel == CM_LARGE_PIC
 		  && DEFAULT_ABI != MS_ABI))
 	  && GET_CODE (XEXP (fnaddr, 0)) == SYMBOL_REF
-	  && ! SYMBOL_REF_LOCAL_P (XEXP (fnaddr, 0)))
+	  && !SYMBOL_REF_LOCAL_P (XEXP (fnaddr, 0))
+	  && flag_plt
+	  && (SYMBOL_REF_DECL ((XEXP (fnaddr, 0))) == NULL_TREE
+	      || !lookup_attribute ("noplt",
+		     DECL_ATTRIBUTES (SYMBOL_REF_DECL (XEXP (fnaddr, 0))))))
 	{
 	  use_reg (&use, gen_rtx_REG (Pmode, REAL_PIC_OFFSET_TABLE_REGNUM));
 	  if (ix86_use_pseudo_pic_reg ())
@@ -25597,6 +25603,31 @@ ix86_expand_call (rtx retval, rtx fnaddr, rtx callarg1,
   return call;
 }
 
+/* Return true if the function being called was marked with attribute "noplt"
+   or using -fno-plt and we are compiling for non-PIC and x86_64.  We need to
+   handle the non-PIC case in the backend because there is no easy interface
+   for the front-end to force non-PLT calls to use the GOT.  This is currently
+   used only with 64-bit ELF targets to call the function marked "noplt"
+   indirectly.  */
+
+static bool
+ix86_nopic_noplt_attribute_p (rtx call_op)
+{
+  if (flag_pic || ix86_cmodel == CM_LARGE
+      || !TARGET_64BIT || TARGET_MACHO || TARGET_SEH || TARGET_PECOFF
+      || SYMBOL_REF_LOCAL_P (call_op))
+    return false;
+
+  tree symbol_decl = SYMBOL_REF_DECL (call_op);
+
+  if (!flag_plt
+      || (symbol_decl != NULL_TREE
+          && lookup_attribute ("noplt", DECL_ATTRIBUTES (symbol_decl))))
+    return true;
+
+  return false;
+}
+
 /* Output the assembly for a call instruction.  */
 
 const char *
@@ -25608,7 +25639,9 @@ ix86_output_call_insn (rtx_insn *insn, rtx call_op)
 
   if (SIBLING_CALL_P (insn))
     {
-      if (direct_p)
+      if (direct_p && ix86_nopic_noplt_attribute_p (call_op))
+	xasm = "%!jmp\t*%p0@GOTPCREL(%%rip)";
+      else if (direct_p)
 	xasm = "%!jmp\t%P0";
       /* SEH epilogue detection requires the indirect branch case
 	 to include REX.W.  */
@@ -25651,7 +25684,9 @@ ix86_output_call_insn (rtx_insn *insn, rtx call_op)
 	seh_nop_p = true;
     }
 
-  if (direct_p)
+  if (direct_p && ix86_nopic_noplt_attribute_p (call_op))
+    xasm = "%!call\t*%p0@GOTPCREL(%%rip)";
+  else if (direct_p)
     xasm = "%!call\t%P0";
   else
     xasm = "%!call\t%A0";