Properly handle -fno-plt in ix86_expand_callhjl/pr67215/master

It boils down to that -fno-plt should convert calling an external
function, foo, from

call foo@PLT

to

call *foo@GOT

to avoid one extra direct branch to PLT.  The proper place for this is
in backend during expanding a function call.  The backend already takes
care of many details for calling an external function, like setting up
a PIC register.  Using the GOT slot instead of PLT slot is just one of
those details.  For x86, it should be done in ix86_expand_call, not
prepare_call_address and hoping for the best, which doesn't always
happen.  Also non-PIC case can only be handled in backend.

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.

sibcall_memory_operand is also updated to accept the GOT slot so that

call *foo@GOT(%reg)

can be generated by ix86_expand_call for 32-bit and 64-bit large model.

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.

4 files changed, 95 insertions, 28 deletions

diff --git a/gcc/calls.c b/gcc/calls.c
index 026cb53eed9..22c65cd9a0a 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 c69c738caa0..91e9e29e3a6 100644
--- a/gcc/config/i386/i386.c
+++ b/gcc/config/i386/i386.c
@@ -25649,21 +25649,54 @@ 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);
+	      /* Pmode may not be the same as word_mode for x32, which
+		 doesn't support indirect branch via 32-bit memory slot.
+		 Since x32 GOT slot is 64 bit with zero upper 32 bits,
+		 indirect branch via x32 GOT slot is OK.  */
+	      if (GET_MODE (fnaddr) != word_mode)
+		fnaddr = gen_rtx_ZERO_EXTEND (word_mode, fnaddr);
+	      fnaddr = gen_rtx_MEM (QImode, fnaddr);
+	    }
 	}
     }
 
@@ -25685,9 +25718,15 @@ 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))
+  /* Since x32 GOT slot is 64 bit with zero upper 32 bits, indirect
+     branch via x32 GOT slot is OK.  */
+  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 00000000000..fd37f8e63db
--- /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 00000000000..ebf2919078c
--- /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" } } */