[AArch64, 3/6] Restrict indirect tail calls to x16 and x17

This patch is part of a series that enables ARMv8.5-A in GCC and
adds Branch Target Identification Mechanism.

This patch changes the registers that are allowed for indirect tail calls.
We are choosing to restrict these to only x16 or x17.

Indirect tail calls are special in a way that they convert a call statement
(BLR instruction) to a jump statement (BR instruction). For the best possible
use of Branch Target Identification Mechanism, we would like to place a
"BTI C" (call) at the beginning of the function which is only
compatible with BLRs and BR X16/X17. In order to make indirect tail calls
compatible with this scenario, we are restricting the TAILCALL_ADDR_REGS.

In order to use x16/x17 for this purpose, we also had to change the use
of these registers in the epilogue/prologue handling. For this purpose
we are now using x12 and x13 named as EP0_REGNUM and EP1_REGNUM as
scratch registers for epilogue and prologue.

*** gcc/ChangeLog***

2018-01-09  Sudakshina Das  <sudi.das@arm.com>

	* config/aarch64/aarch64.c (aarch64_expand_prologue): Use new
	epilogue/prologue scratch registers EP0_REGNUM and EP1_REGNUM.
	(aarch64_expand_epilogue): Likewise.
	(aarch64_output_mi_thunk): Likewise
	* config/aarch64/aarch64.h (REG_CLASS_CONTENTS): Change
	TAILCALL_ADDR_REGS to x16 and x17.
	* config/aarch64/aarch64.md: Define EP0_REGNUM and EP1_REGNUM.

*** gcc/testsuite/ChangeLog ***

2018-01-09  Sudakshina Das  <sudi.das@arm.com>

	* gcc.target/aarch64/test_frame_17.c: Update to check for EP0_REGNUM
	instead of IP0_REGNUM and add test case.

From-SVN: r267767

gcc/ChangeLog

 2018-01-09  Sudakshina Das  <sudi.das@arm.com>
 
+	* config/aarch64/aarch64.c (aarch64_expand_prologue): Use new
+	epilogue/prologue scratch registers EP0_REGNUM and EP1_REGNUM.
+	(aarch64_expand_epilogue): Likewise.
+	(aarch64_output_mi_thunk): Likewise
+	* config/aarch64/aarch64.h (REG_CLASS_CONTENTS): Change
+	TAILCALL_ADDR_REGS to x16 and x17.
+	* config/aarch64/aarch64.md: Define EP0_REGNUM and EP1_REGNUM.
+
+2018-01-09  Sudakshina Das  <sudi.das@arm.com>
+
 	* config/aarch64/aarch64-option-extensions.def: Define
 	AARCH64_OPT_EXTENSION for memtag, rng, sb, ssbs and predres.
 	* gcc/config/aarch64/aarch64.h (AARCH64_FL_RNG): New.

gcc/config/aarch64/aarch64.c

@@ -5521,8 +5521,8 @@ aarch64_expand_prologue (void)
 	aarch64_emit_probe_stack_range (get_stack_check_protect (), frame_size);
     }
 
-  rtx ip0_rtx = gen_rtx_REG (Pmode, IP0_REGNUM);
-  rtx ip1_rtx = gen_rtx_REG (Pmode, IP1_REGNUM);
+  rtx tmp0_rtx = gen_rtx_REG (Pmode, EP0_REGNUM);
+  rtx tmp1_rtx = gen_rtx_REG (Pmode, EP1_REGNUM);
 
   /* In theory we should never have both an initial adjustment
      and a callee save adjustment.  Verify that is the case since the
@@ -5532,7 +5532,7 @@ aarch64_expand_prologue (void)
   /* Will only probe if the initial adjustment is larger than the guard
      less the amount of the guard reserved for use by the caller's
      outgoing args.  */
-  aarch64_allocate_and_probe_stack_space (ip0_rtx, ip1_rtx, initial_adjust,
+  aarch64_allocate_and_probe_stack_space (tmp0_rtx, tmp1_rtx, initial_adjust,
 					  true, false);
 
   if (callee_adjust != 0)
@@ -5550,7 +5550,7 @@ aarch64_expand_prologue (void)
 	}
       aarch64_add_offset (Pmode, hard_frame_pointer_rtx,
 			  stack_pointer_rtx, callee_offset,
-			  ip1_rtx, ip0_rtx, frame_pointer_needed);
+			  tmp1_rtx, tmp0_rtx, frame_pointer_needed);
       if (frame_pointer_needed && !frame_size.is_constant ())
 	{
 	  /* Variable-sized frames need to describe the save slot
@@ -5596,7 +5596,7 @@ aarch64_expand_prologue (void)
 
   /* We may need to probe the final adjustment if it is larger than the guard
      that is assumed by the called.  */
-  aarch64_allocate_and_probe_stack_space (ip1_rtx, ip0_rtx, final_adjust,
+  aarch64_allocate_and_probe_stack_space (tmp1_rtx, tmp0_rtx, final_adjust,
 					  !frame_pointer_needed, true);
 }
 
@@ -5647,8 +5647,8 @@ aarch64_expand_epilogue (bool for_sibcall)
   unsigned reg2 = cfun->machine->frame.wb_candidate2;
   rtx cfi_ops = NULL;
   rtx_insn *insn;
-  /* A stack clash protection prologue may not have left IP0_REGNUM or
-     IP1_REGNUM in a usable state.  The same is true for allocations
+  /* A stack clash protection prologue may not have left EP0_REGNUM or
+     EP1_REGNUM in a usable state.  The same is true for allocations
      with an SVE component, since we then need both temporary registers
      for each allocation.  For stack clash we are in a usable state if
      the adjustment is less than GUARD_SIZE - GUARD_USED_BY_CALLER.  */
@@ -5663,8 +5663,8 @@ aarch64_expand_epilogue (bool for_sibcall)
   bool can_inherit_p = (initial_adjust.is_constant ()
 			&& final_adjust.is_constant ())
 			&& (!flag_stack_clash_protection
-			     || known_lt (initial_adjust,
-					  guard_size - guard_used_by_caller));
+			    || known_lt (initial_adjust,
+					 guard_size - guard_used_by_caller));
 
   /* We need to add memory barrier to prevent read from deallocated stack.  */
   bool need_barrier_p
@@ -5682,20 +5682,20 @@ aarch64_expand_epilogue (bool for_sibcall)
 
   /* Restore the stack pointer from the frame pointer if it may not
      be the same as the stack pointer.  */
-  rtx ip0_rtx = gen_rtx_REG (Pmode, IP0_REGNUM);
-  rtx ip1_rtx = gen_rtx_REG (Pmode, IP1_REGNUM);
+  rtx tmp0_rtx = gen_rtx_REG (Pmode, EP0_REGNUM);
+  rtx tmp1_rtx = gen_rtx_REG (Pmode, EP1_REGNUM);
   if (frame_pointer_needed
       && (maybe_ne (final_adjust, 0) || cfun->calls_alloca))
     /* If writeback is used when restoring callee-saves, the CFA
        is restored on the instruction doing the writeback.  */
     aarch64_add_offset (Pmode, stack_pointer_rtx,
 			hard_frame_pointer_rtx, -callee_offset,
-			ip1_rtx, ip0_rtx, callee_adjust == 0);
+			tmp1_rtx, tmp0_rtx, callee_adjust == 0);
   else
      /* The case where we need to re-use the register here is very rare, so
 	avoid the complicated condition and just always emit a move if the
 	immediate doesn't fit.  */
-     aarch64_add_sp (ip1_rtx, ip0_rtx, final_adjust, true);
+     aarch64_add_sp (tmp1_rtx, tmp0_rtx, final_adjust, true);
 
   aarch64_restore_callee_saves (DImode, callee_offset, R0_REGNUM, R30_REGNUM,
 				callee_adjust != 0, &cfi_ops);
@@ -5722,8 +5722,11 @@ aarch64_expand_epilogue (bool for_sibcall)
       cfi_ops = NULL;
     }
 
-  aarch64_add_sp (ip0_rtx, ip1_rtx, initial_adjust,
-		  !can_inherit_p || df_regs_ever_live_p (IP0_REGNUM));
+  /* Liveness of EP0_REGNUM can not be trusted across function calls either, so
+     add restriction on emit_move optimization to leaf functions.  */
+  aarch64_add_sp (tmp0_rtx, tmp1_rtx, initial_adjust,
+		  (!can_inherit_p || !crtl->is_leaf
+		   || df_regs_ever_live_p (EP0_REGNUM)));
 
   if (cfi_ops)
     {
@@ -5829,8 +5832,8 @@ aarch64_output_mi_thunk (FILE *file, tree thunk ATTRIBUTE_UNUSED,
   emit_note (NOTE_INSN_PROLOGUE_END);
 
   this_rtx = gen_rtx_REG (Pmode, this_regno);
-  temp0 = gen_rtx_REG (Pmode, IP0_REGNUM);
-  temp1 = gen_rtx_REG (Pmode, IP1_REGNUM);
+  temp0 = gen_rtx_REG (Pmode, EP0_REGNUM);
+  temp1 = gen_rtx_REG (Pmode, EP1_REGNUM);
 
   if (vcall_offset == 0)
     aarch64_add_offset (Pmode, this_rtx, this_rtx, delta, temp1, temp0, false);

gcc/config/aarch64/aarch64.h

@@ -579,7 +579,7 @@ enum reg_class
 #define REG_CLASS_CONTENTS						\
 {									\
   { 0x00000000, 0x00000000, 0x00000000 },	/* NO_REGS */		\
-  { 0x0004ffff, 0x00000000, 0x00000000 },	/* TAILCALL_ADDR_REGS */\
+  { 0x00030000, 0x00000000, 0x00000000 },	/* TAILCALL_ADDR_REGS */\
   { 0x7fffffff, 0x00000000, 0x00000003 },	/* GENERAL_REGS */	\
   { 0x80000000, 0x00000000, 0x00000000 },	/* STACK_REG */		\
   { 0xffffffff, 0x00000000, 0x00000003 },	/* POINTER_REGS */	\

gcc/config/aarch64/aarch64.md

@@ -35,6 +35,9 @@
     (R11_REGNUM		11)
     (R12_REGNUM		12)
     (R13_REGNUM		13)
+    ;; Scratch registers for prologue/epilogue use.
+    (EP0_REGNUM		12)
+    (EP1_REGNUM		13)
     (R14_REGNUM		14)
     (R15_REGNUM		15)
     (R16_REGNUM		16)

gcc/testsuite/ChangeLog

+2018-01-09  Sudakshina Das  <sudi.das@arm.com>
+
+	* gcc.target/aarch64/test_frame_17.c: Update to check for EP0_REGNUM
+	instead of IP0_REGNUM and add test case.
+
 2019-01-09  Alejandro Martinez  <alejandro.martinezvicente@arm.com>
 
 	* gcc.target/aarch64/sve/copysign_1.c: New test for SVE vectorized

gcc/testsuite/gcc.target/aarch64/test_frame_17.c

 /* { dg-do compile } */
-/* { dg-options "-O2 --save-temps" } */
+/* { dg-options "-O2" } */
 
 /* Test reuse of stack adjustment temporaries.  */
 
 void foo ();
 
+/* Should only use 1 mov and re-use it.  */
 int reuse_mov (int i)
 {
   int arr[1025];
   return arr[i];
 }
 
+/* Should use 2 movs because x12 is live.  */
+int no_reuse_mov_live (int i)
+{
+  int arr[1025];
+  register long long a __asm("x12");
+  a = a+1;
+  return arr[i] + a;
+}
+
+/* Should use 2 movs because its not a leaf function.  */
 int no_reuse_mov (int i)
 {
   int arr[1025];
@@ -18,4 +29,4 @@ int no_reuse_mov (int i)
   return arr[i];
 }
 
-/* { dg-final { scan-assembler-times "mov\tx16, \[0-9\]+" 3 } } */
+/* { dg-final { scan-assembler-times "mov\tx12, \[0-9\]+" 5 } } */