Improve stack adjustment by reusing a temporary move immediate from the epilog...

Improve stack adjustment by reusing a temporary move immediate from the epilog
if the register is still valid in the epilog.  This generates smaller code for
leaf functions with a stack size of more then 4KB.

gcc/
	* config/aarch64/aarch64.c (aarch64_add_constant_internal):
	Add extra argument to allow emitting the move immediate.
	Use add/sub with positive immediate.
	(aarch64_add_constant): Add inline function.
	(aarch64_add_sp): Likewise.
	(aarch64_sub_sp): Likewise.
	(aarch64_expand_prologue): Call aarch64_sub_sp.
	(aarch64_expand_epilogue): Call aarch64_add_sp.
	Decide when to leave out move.
	(aarch64_output_mi_thunk): Call aarch64_add_constant.

testsuite/
	* gcc.target/aarch64/test_frame_17.c: New test.

From-SVN: r241420

3 files changed, 68 insertions, 25 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 0625c00..a2f8641 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,5 +1,18 @@
 2016-10-21  Wilco Dijkstra  <wdijkstr@arm.com>
 
+	* config/aarch64/aarch64.c (aarch64_add_constant_internal):
+	Add extra argument to allow emitting the move immediate.
+	Use add/sub with positive immediate.
+	(aarch64_add_constant): Add inline function.
+	(aarch64_add_sp): Likewise.
+	(aarch64_sub_sp): Likewise.
+	(aarch64_expand_prologue): Call aarch64_sub_sp.
+	(aarch64_expand_epilogue): Call aarch64_add_sp.
+	Decide when to leave out move.
+	(aarch64_output_mi_thunk): Call aarch64_add_constant.
+
+2016-10-21  Wilco Dijkstra  <wdijkstr@arm.com>
+
 	* config/aarch64/aarch64.c (aarch64_layout_frame):
 	Align FP callee-saves.
 
diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
index 584e1f5..df74ad9 100644
--- a/gcc/config/aarch64/aarch64.c
+++ b/gcc/config/aarch64/aarch64.c
@@ -1954,26 +1954,31 @@ aarch64_expand_mov_immediate (rtx dest, rtx imm)
   aarch64_internal_mov_immediate (dest, imm, true, GET_MODE (dest));
 }
 
-/* Add DELTA to REGNUM in mode MODE.  SCRATCHREG can be used to held
-   intermediate value if necessary.
-
-   This function is sometimes used to adjust the stack pointer, so we must
-   ensure that it can never cause transient stack deallocation by writing an
-   invalid value into REGNUM.  */
+/* Add DELTA to REGNUM in mode MODE.  SCRATCHREG can be used to hold a
+   temporary value if necessary.  FRAME_RELATED_P should be true if
+   the RTX_FRAME_RELATED flag should be set and CFA adjustments added
+   to the generated instructions.  If SCRATCHREG is known to hold
+   abs (delta), EMIT_MOVE_IMM can be set to false to avoid emitting the
+   immediate again.
+
+   Since this function may be used to adjust the stack pointer, we must
+   ensure that it cannot cause transient stack deallocation (for example
+   by first incrementing SP and then decrementing when adjusting by a
+   large immediate).  */
 
 static void
-aarch64_add_constant (machine_mode mode, int regnum, int scratchreg,
-		      HOST_WIDE_INT delta, bool frame_related_p)
+aarch64_add_constant_internal (machine_mode mode, int regnum, int scratchreg,
+			       HOST_WIDE_INT delta, bool frame_related_p,
+			       bool emit_move_imm)
 {
   HOST_WIDE_INT mdelta = abs_hwi (delta);
   rtx this_rtx = gen_rtx_REG (mode, regnum);
   rtx_insn *insn;
 
-  /* Do nothing if mdelta is zero.  */
   if (!mdelta)
     return;
 
-  /* We only need single instruction if the offset fit into add/sub.  */
+  /* Single instruction adjustment.  */
   if (aarch64_uimm12_shift (mdelta))
     {
       insn = emit_insn (gen_add2_insn (this_rtx, GEN_INT (delta)));
@@ -1981,11 +1986,10 @@ aarch64_add_constant (machine_mode mode, int regnum, int scratchreg,
       return;
     }
 
-  /* We need two add/sub instructions, each one performing part of the
-     calculation.  Don't do this if the addend can be loaded into register with
-     a single instruction, in that case we prefer a move to a scratch register
-     following by an addition.  */
-  if (mdelta < 0x1000000 && !aarch64_move_imm (delta, mode))
+  /* Emit 2 additions/subtractions if the adjustment is less than 24 bits.
+     Only do this if mdelta is not a 16-bit move as adjusting using a move
+     is better.  */
+  if (mdelta < 0x1000000 && !aarch64_move_imm (mdelta, mode))
     {
       HOST_WIDE_INT low_off = mdelta & 0xfff;
 
@@ -1997,10 +2001,12 @@ aarch64_add_constant (machine_mode mode, int regnum, int scratchreg,
       return;
     }
 
-  /* Otherwise use generic function to handle all other situations.  */
+  /* Emit a move immediate if required and an addition/subtraction.  */
   rtx scratch_rtx = gen_rtx_REG (mode, scratchreg);
-  aarch64_internal_mov_immediate (scratch_rtx, GEN_INT (delta), true, mode);
-  insn = emit_insn (gen_add2_insn (this_rtx, scratch_rtx));
+  if (emit_move_imm)
+    aarch64_internal_mov_immediate (scratch_rtx, GEN_INT (mdelta), true, mode);
+  insn = emit_insn (delta < 0 ? gen_sub2_insn (this_rtx, scratch_rtx)
+			      : gen_add2_insn (this_rtx, scratch_rtx));
   if (frame_related_p)
     {
       RTX_FRAME_RELATED_P (insn) = frame_related_p;
@@ -2009,6 +2015,27 @@ aarch64_add_constant (machine_mode mode, int regnum, int scratchreg,
     }
 }
 
+static inline void
+aarch64_add_constant (machine_mode mode, int regnum, int scratchreg,
+		      HOST_WIDE_INT delta)
+{
+  aarch64_add_constant_internal (mode, regnum, scratchreg, delta, false, true);
+}
+
+static inline void
+aarch64_add_sp (int scratchreg, HOST_WIDE_INT delta, bool emit_move_imm)
+{
+  aarch64_add_constant_internal (Pmode, SP_REGNUM, scratchreg, delta,
+				 true, emit_move_imm);
+}
+
+static inline void
+aarch64_sub_sp (int scratchreg, HOST_WIDE_INT delta, bool frame_related_p)
+{
+  aarch64_add_constant_internal (Pmode, SP_REGNUM, scratchreg, -delta,
+				 frame_related_p, true);
+}
+
 static bool
 aarch64_function_ok_for_sibcall (tree decl ATTRIBUTE_UNUSED,
 				 tree exp ATTRIBUTE_UNUSED)
@@ -3230,7 +3257,7 @@ aarch64_expand_prologue (void)
 	aarch64_emit_probe_stack_range (STACK_CHECK_PROTECT, frame_size);
     }
 
-  aarch64_add_constant (Pmode, SP_REGNUM, IP0_REGNUM, -initial_adjust, true);
+  aarch64_sub_sp (IP0_REGNUM, initial_adjust, true);
 
   if (callee_adjust != 0)
     aarch64_push_regs (reg1, reg2, callee_adjust);
@@ -3251,8 +3278,7 @@ aarch64_expand_prologue (void)
 			     callee_adjust != 0 || frame_pointer_needed);
   aarch64_save_callee_saves (DFmode, callee_offset, V0_REGNUM, V31_REGNUM,
 			     callee_adjust != 0 || frame_pointer_needed);
-  aarch64_add_constant (Pmode, SP_REGNUM, IP1_REGNUM, -final_adjust,
-			!frame_pointer_needed);
+  aarch64_sub_sp (IP1_REGNUM, final_adjust, !frame_pointer_needed);
 }
 
 /* Return TRUE if we can use a simple_return insn.
@@ -3317,7 +3343,7 @@ aarch64_expand_epilogue (bool for_sibcall)
       RTX_FRAME_RELATED_P (insn) = callee_adjust == 0;
     }
   else
-    aarch64_add_constant (Pmode, SP_REGNUM, IP1_REGNUM, final_adjust, true);
+    aarch64_add_sp (IP1_REGNUM, final_adjust, df_regs_ever_live_p (IP1_REGNUM));
 
   aarch64_restore_callee_saves (DImode, callee_offset, R0_REGNUM, R30_REGNUM,
 				callee_adjust != 0, &cfi_ops);
@@ -3340,7 +3366,7 @@ aarch64_expand_epilogue (bool for_sibcall)
       cfi_ops = NULL;
     }
 
-  aarch64_add_constant (Pmode, SP_REGNUM, IP0_REGNUM, initial_adjust, true);
+  aarch64_add_sp (IP0_REGNUM, initial_adjust, df_regs_ever_live_p (IP0_REGNUM));
 
   if (cfi_ops)
     {
@@ -3435,7 +3461,7 @@ aarch64_output_mi_thunk (FILE *file, tree thunk ATTRIBUTE_UNUSED,
   emit_note (NOTE_INSN_PROLOGUE_END);
 
   if (vcall_offset == 0)
-    aarch64_add_constant (Pmode, this_regno, IP1_REGNUM, delta, false);
+    aarch64_add_constant (Pmode, this_regno, IP1_REGNUM, delta);
   else
     {
       gcc_assert ((vcall_offset & (POINTER_BYTES - 1)) == 0);
@@ -3451,7 +3477,7 @@ aarch64_output_mi_thunk (FILE *file, tree thunk ATTRIBUTE_UNUSED,
 	    addr = gen_rtx_PRE_MODIFY (Pmode, this_rtx,
 				       plus_constant (Pmode, this_rtx, delta));
 	  else
-	    aarch64_add_constant (Pmode, this_regno, IP1_REGNUM, delta, false);
+	    aarch64_add_constant (Pmode, this_regno, IP1_REGNUM, delta);
 	}
 
       if (Pmode == ptr_mode)
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index b89c6ce..e3726c7 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,7 @@
+2016-10-21  Wilco Dijkstra  <wdijkstr@arm.com>
+
+	* gcc.target/aarch64/test_frame_17.c: New test.
+
 2016-10-21  Andris Pavenis  <andris.pavenis@iki.fi>
 
 	PR preprocessor/71681