RFC: [PATCH] PR target/67215: -fno-plt needs improvements for x86

["H.J. Lu" <hjl.tools@gmail.com>]

prepare_call_address in calls.c is the wrong place to handle -fno-plt.
We shoudn't force function address into register and hope that load
function address via GOT and indirect call via register will be folded
into indirect call via GOT, which doesn't always happen.  Allso non-PIC
case can only be handled in backend.  Instead, backend should expand
external function call into indirect call via GOT for -fno-plt.

This patch reverts -fno-plt in prepare_call_address and handles it in
ix86_expand_call.  Other backends may need similar changes to support
-fno-plt.  Alternately, we can introduce a target hook to indicate
whether an external function should be called via register for -fno-plt
so that i386 backend can disable it in prepare_call_address.

Any comments?

H.J.
--
gcc/

	PR target/67215
	* calls.c (prepare_call_address): Don't handle -fno-plt here.
	* config/i386/i386.c (ix86_expand_call): Generate indirect call
	via GOT for -fno-plt.  Support indirect call via GOT for x32.

gcc/testsuite/

	PR target/67215
	* gcc.target/i386/pr67215-1.c: New test.
	* gcc.target/i386/pr67215-2.c: Likewise.
---
 gcc/calls.c                               | 12 ------
 gcc/config/i386/i386.c                    | 65 +++++++++++++++++++++++--------
 gcc/testsuite/gcc.target/i386/pr67215-1.c | 20 ++++++++++
 gcc/testsuite/gcc.target/i386/pr67215-2.c | 20 ++++++++++
 4 files changed, 89 insertions(+), 28 deletions(-)
 create mode 100644 gcc/testsuite/gcc.target/i386/pr67215-1.c
 create mode 100644 gcc/testsuite/gcc.target/i386/pr67215-2.c

diff --git a/gcc/calls.c b/gcc/calls.c
index 5636725..7cce9be 100644
--- a/gcc/calls.c
+++ b/gcc/calls.c
@@ -203,18 +203,6 @@ prepare_call_address (tree fndecl_or_type, rtx funexp, rtx static_chain_value,
 	       && targetm.small_register_classes_for_mode_p (FUNCTION_MODE))
 	      ? force_not_mem (memory_address (FUNCTION_MODE, funexp))
 	      : memory_address (FUNCTION_MODE, funexp));
-  else if (flag_pic
-	   && fndecl_or_type
-	   && TREE_CODE (fndecl_or_type) == FUNCTION_DECL
-	   && (!flag_plt
-	       || lookup_attribute ("noplt", DECL_ATTRIBUTES (fndecl_or_type)))
-	   && !targetm.binds_local_p (fndecl_or_type))
-    {
-      /* This is done only for PIC code.  There is no easy interface to force the
-	 function address into GOT for non-PIC case.  non-PIC case needs to be
-	 handled specially by the backend.  */
-      funexp = force_reg (Pmode, funexp);
-    }
   else if (! sibcallp)
     {
       if (!NO_FUNCTION_CSE && optimize && ! flag_no_function_cse)
diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
index 4a0986c..bf8a21d 100644
--- a/gcc/config/i386/i386.c
+++ b/gcc/config/i386/i386.c
@@ -25650,21 +25650,50 @@ ix86_expand_call (rtx retval, rtx fnaddr, rtx callarg1,
       /* 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.  */
+      rtx addr = XEXP (fnaddr, 0);
       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))
-	  && flag_plt
-	  && (SYMBOL_REF_DECL ((XEXP (fnaddr, 0))) == NULL_TREE
-	      || !lookup_attribute ("noplt",
-		     DECL_ATTRIBUTES (SYMBOL_REF_DECL (XEXP (fnaddr, 0))))))
+	  && GET_CODE (addr) == SYMBOL_REF
+	  && !SYMBOL_REF_LOCAL_P (addr))
 	{
-	  use_reg (&use, gen_rtx_REG (Pmode, REAL_PIC_OFFSET_TABLE_REGNUM));
-	  if (ix86_use_pseudo_pic_reg ())
-	    emit_move_insn (gen_rtx_REG (Pmode, REAL_PIC_OFFSET_TABLE_REGNUM),
-			    pic_offset_table_rtx);
+	  if (flag_plt
+	      && (SYMBOL_REF_DECL (addr) == NULL_TREE
+		  || !lookup_attribute ("noplt",
+					DECL_ATTRIBUTES (SYMBOL_REF_DECL (addr)))))
+	    {
+	      if (!TARGET_64BIT
+		  || (ix86_cmodel == CM_LARGE_PIC
+		      && DEFAULT_ABI != MS_ABI))
+		{
+		  use_reg (&use, gen_rtx_REG (Pmode,
+					      REAL_PIC_OFFSET_TABLE_REGNUM));
+		  if (ix86_use_pseudo_pic_reg ())
+		    emit_move_insn (gen_rtx_REG (Pmode,
+						 REAL_PIC_OFFSET_TABLE_REGNUM),
+				    pic_offset_table_rtx);
+		}
+	    }
+	  else if (!TARGET_PECOFF && !TARGET_MACHO)
+	    {
+	      if (TARGET_64BIT)
+		{
+		  fnaddr = gen_rtx_UNSPEC (Pmode,
+					   gen_rtvec (1, addr),
+					   UNSPEC_GOTPCREL);
+		  fnaddr = gen_rtx_CONST (Pmode, fnaddr);
+		}
+	      else
+		{
+		  fnaddr = gen_rtx_UNSPEC (Pmode, gen_rtvec (1, addr),
+					   UNSPEC_GOT);
+		  fnaddr = gen_rtx_CONST (Pmode, fnaddr);
+		  fnaddr = gen_rtx_PLUS (Pmode, pic_offset_table_rtx,
+					 fnaddr);
+		}
+	      fnaddr = gen_const_mem (Pmode, fnaddr);
+	      if (GET_MODE (fnaddr) != word_mode)
+		fnaddr = gen_rtx_ZERO_EXTEND (word_mode, fnaddr);
+	      fnaddr = gen_rtx_MEM (QImode, fnaddr);
+	    }
 	}
     }
 
@@ -25686,9 +25715,13 @@ ix86_expand_call (rtx retval, rtx fnaddr, rtx callarg1,
       && GET_CODE (XEXP (fnaddr, 0)) == SYMBOL_REF
       && !local_symbolic_operand (XEXP (fnaddr, 0), VOIDmode))
     fnaddr = gen_rtx_MEM (QImode, construct_plt_address (XEXP (fnaddr, 0)));
-  else if (sibcall
-	   ? !sibcall_insn_operand (XEXP (fnaddr, 0), word_mode)
-	   : !call_insn_operand (XEXP (fnaddr, 0), word_mode))
+  else if (!(TARGET_X32
+	     && MEM_P (fnaddr)
+	     && GET_CODE (XEXP (fnaddr, 0)) == ZERO_EXTEND
+	     && GOT_memory_operand (XEXP (XEXP (fnaddr, 0), 0), Pmode))
+	   && (sibcall
+	       ? !sibcall_insn_operand (XEXP (fnaddr, 0), word_mode)
+	       : !call_insn_operand (XEXP (fnaddr, 0), word_mode)))
     {
       fnaddr = convert_to_mode (word_mode, XEXP (fnaddr, 0), 1);
       fnaddr = gen_rtx_MEM (QImode, copy_to_mode_reg (word_mode, fnaddr));
diff --git a/gcc/testsuite/gcc.target/i386/pr67215-1.c b/gcc/testsuite/gcc.target/i386/pr67215-1.c
new file mode 100644
index 0000000..fd37f8e
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr67215-1.c
@@ -0,0 +1,20 @@
+/* { dg-do compile { target *-*-linux* } } */
+/* { dg-options "-O2 -fpic -fno-plt" } */
+
+extern char* bar (int);
+extern char* arr[32];
+
+void
+foo (void)
+{
+  int i;
+
+  for (i = 0; i < 32; i++)
+    arr[i] = bar (128);
+}
+
+/* { dg-final { scan-assembler "call\[ \t\]*.bar@GOTPCREL" { target { ! ia32 } } } } */
+/* { dg-final { scan-assembler "call\[ \t\]*.bar@GOT\\(" { target ia32 } } } */
+/* { dg-final { scan-assembler-not "mov(l|q)\[ \t\]*.bar@GOTPCREL" { target { ! ia32 } } } } */
+/* { dg-final { scan-assembler-not "movl\[ \t\]*.bar@GOT\\(" { target ia32 } } } */
+/* { dg-final { scan-assembler-not "call\[ \t\]*.bar@PLT" } } */
diff --git a/gcc/testsuite/gcc.target/i386/pr67215-2.c b/gcc/testsuite/gcc.target/i386/pr67215-2.c
new file mode 100644
index 0000000..ebf2919
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr67215-2.c
@@ -0,0 +1,20 @@
+/* { dg-do compile { target *-*-linux* } } */
+/* { dg-options "-O2 -fpic" } */
+
+extern char* bar (int) __attribute__ ((noplt));
+extern char* arr[32];
+
+void
+foo (void)
+{
+  int i;
+
+  for (i = 0; i < 32; i++)
+    arr[i] = bar (128);
+}
+
+/* { dg-final { scan-assembler "call\[ \t\]*.bar@GOTPCREL" { target { ! ia32 } } } } */
+/* { dg-final { scan-assembler "call\[ \t\]*.bar@GOT\\(" { target ia32 } } } */
+/* { dg-final { scan-assembler-not "mov(l|q)\[ \t\]*.bar@GOTPCREL" { target { ! ia32 } } } } */
+/* { dg-final { scan-assembler-not "movl\[ \t\]*.bar@GOT\\(" { target ia32 } } } */
+/* { dg-final { scan-assembler-not "call\[ \t\]*.bar@PLT" } } */
-- 
2.4.3