[AArch64] Improve TLS Descriptor pattern to release RTL loop IV opt

[Jiong Wang <jiong dot wang at arm dot com>]

The instruction sequences for preparing argument for TLS descriptor
runtime resolver and the later function call to resolver can actually be
hoisted out of the loop.

Currently we can't because we have exposed the hard register X0 as
destination of "set".  While GCC's RTL data flow infrastructure will
skip or do very conservative assumption when hard register involved in
and thus some loop IV opportunities are missed.

This patch add another "tlsdesc_small_pseudo_<mode>" pattern, and avoid
expose x0 to gcc generic code.

Generally, we define a new register class FIXED_R0 which only contains register
0, so the instruction sequences generated from the new add pattern is the same
as tlsdesc_small_<mode>, while the operand 0 is wrapped as pseudo register that
RTL IV opt can handle it.

Ideally, we should allow operand 0 to be any pseudo register, but then
we can't model the override of x0 caused by the function call which is
hidded by the UNSPEC.

So here, we restricting operand 0 to be x0, the override of x0 can be
reflected to the gcc.

OK for trunk?

2015-07-28  Ramana Radhakrishnan  <ramana.radhakrishnan@arm.com>
            Jiong Wang  <jiong.wang@arm.com>

gcc/
  * config/aarch64/aarch64.d (tlsdesc_small_pseudo_<mode>): New pattern.
  * config/aarch64/aarch64.h (reg_class): New enumeration FIXED_REG0.
  (REG_CLASS_NAMES): Likewise.
  (REG_CLASS_CONTENTS): Likewise.
  * config/aarch64/aarch64.c (aarch64_class_max_nregs): Likewise.
  (aarch64_register_move_cost): Likewise.
  (aarch64_load_symref_appropriately): Invoke the new added pattern if
  possible.
  * config/aarch64/constraints.md (Uc0): New constraint.

gcc/testsuite.
  * gcc.target/aarch64/tlsdesc_hoist.c: New testcase.

-- 
Regards,
Jiong

diff --git a/gcc/config/aarch64/aarch64.h b/gcc/config/aarch64/aarch64.h
index 3851564..fb4834a 100644
--- a/gcc/config/aarch64/aarch64.h
+++ b/gcc/config/aarch64/aarch64.h
@@ -454,6 +454,7 @@ extern unsigned long aarch64_isa_flags;
 enum reg_class
 {
   NO_REGS,
+  FIXED_REG0,
   CALLER_SAVE_REGS,
   GENERAL_REGS,
   STACK_REG,
@@ -469,6 +470,7 @@ enum reg_class
 #define REG_CLASS_NAMES				\
 {						\
   "NO_REGS",					\
+  "FIXED_REG0"					\
   "CALLER_SAVE_REGS",				\
   "GENERAL_REGS",				\
   "STACK_REG",					\
@@ -481,6 +483,7 @@ enum reg_class
 #define REG_CLASS_CONTENTS						\
 {									\
   { 0x00000000, 0x00000000, 0x00000000 },	/* NO_REGS */		\
+  { 0x00000001, 0x00000000, 0x00000000 },	/* FIXED_REG0 */	\
   { 0x0007ffff, 0x00000000, 0x00000000 },	/* CALLER_SAVE_REGS */	\
   { 0x7fffffff, 0x00000000, 0x00000003 },	/* GENERAL_REGS */	\
   { 0x80000000, 0x00000000, 0x00000000 },	/* STACK_REG */		\
diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
index ef07e05..f1f2cab 100644
--- a/gcc/config/aarch64/aarch64.c
+++ b/gcc/config/aarch64/aarch64.c
@@ -1038,22 +1038,39 @@ aarch64_load_symref_appropriately (rtx dest, rtx imm,
       {
 	machine_mode mode = GET_MODE (dest);
 	rtx x0 = gen_rtx_REG (mode, R0_REGNUM);
+	rtx offset;
 	rtx tp;
 
 	gcc_assert (mode == Pmode || mode == ptr_mode);
 
-	/* In ILP32, the got entry is always of SImode size.  Unlike
-	   small GOT, the dest is fixed at reg 0.  */
-	if (TARGET_ILP32)
-	  emit_insn (gen_tlsdesc_small_si (imm));
+	if (can_create_pseudo_p ())
+	  {
+	    rtx reg = gen_reg_rtx (mode);
+
+	    if (TARGET_ILP32)
+	      emit_insn (gen_tlsdesc_small_pseudo_si (reg, imm));
+	    else
+	      emit_insn (gen_tlsdesc_small_pseudo_di (reg, imm));
+
+	    offset = reg;
+	  }
 	else
-	  emit_insn (gen_tlsdesc_small_di (imm));
+	  {
+	    /* In ILP32, the got entry is always of SImode size.  Unlike
+	       small GOT, the dest is fixed at reg 0.  */
+	    if (TARGET_ILP32)
+	      emit_insn (gen_tlsdesc_small_si (imm));
+	    else
+	      emit_insn (gen_tlsdesc_small_di (imm));
+
+	    offset = x0;
+	  }
 	tp = aarch64_load_tp (NULL);
 
 	if (mode != Pmode)
 	  tp = gen_lowpart (mode, tp);
 
-	emit_insn (gen_rtx_SET (dest, gen_rtx_PLUS (mode, tp, x0)));
+	emit_insn (gen_rtx_SET (dest, gen_rtx_PLUS (mode, tp, offset)));
 	set_unique_reg_note (get_last_insn (), REG_EQUIV, imm);
 	return;
       }
@@ -5099,6 +5116,7 @@ aarch64_class_max_nregs (reg_class_t regclass, machine_mode mode)
 	aarch64_vector_mode_p (mode)
 	  ? (GET_MODE_SIZE (mode) + UNITS_PER_VREG - 1) / UNITS_PER_VREG
 	  : (GET_MODE_SIZE (mode) + UNITS_PER_WORD - 1) / UNITS_PER_WORD;
+    case FIXED_REG0:
     case STACK_REG:
       return 1;
 
@@ -6948,10 +6966,10 @@ aarch64_register_move_cost (machine_mode mode,
     = aarch64_tune_params.regmove_cost;
 
   /* Caller save and pointer regs are equivalent to GENERAL_REGS.  */
-  if (to == CALLER_SAVE_REGS || to == POINTER_REGS)
+  if (to == CALLER_SAVE_REGS || to == POINTER_REGS || to == FIXED_REG0)
     to = GENERAL_REGS;
 
-  if (from == CALLER_SAVE_REGS || from == POINTER_REGS)
+  if (from == CALLER_SAVE_REGS || from == POINTER_REGS || from == FIXED_REG0)
     from = GENERAL_REGS;
 
   /* Moving between GPR and stack cost is the same as GP2GP.  */
diff --git a/gcc/config/aarch64/aarch64.md b/gcc/config/aarch64/aarch64.md
index c681cf1..3fcfe55 100644
--- a/gcc/config/aarch64/aarch64.md
+++ b/gcc/config/aarch64/aarch64.md
@@ -4496,6 +4496,25 @@
   [(set_attr "type" "call")
    (set_attr "length" "16")])
 
+;; The same as tlsdesc_small_<mode> with hard register hiding.
+;; The first operand is actually x0, while we wrap it under a delicated
+;; register class so that before register allocation, it's seen as pseudo
+;; register.  The reason for doing this is we don't expose hard register X0
+;; as the destination of set as it will cause trouble for RTL loop iv.
+;; RTL loop iv will abort ongoing optimization once it finds there is hard reg
+;; as destination of set.
+(define_insn "tlsdesc_small_pseudo_<mode>"
+  [(set (match_operand:PTR 0 "register_operand" "=Uc0")
+	(unspec:PTR [(match_operand 1 "aarch64_valid_symref" "S")]
+		    UNSPEC_TLSDESC))
+   (clobber (reg:DI LR_REGNUM))
+   (clobber (reg:CC CC_REGNUM))
+   (clobber (match_scratch:DI 2 "=r"))]
+  "TARGET_TLS_DESC"
+  "adrp\\t<w>0, %A1\;ldr\\t%<w>2, [%<w>0, #%L1]\;add\\t%<w>0, %<w>0, %L1\;.tlsdesccall\\t%1\;blr\\t%2"
+  [(set_attr "type" "call")
+   (set_attr "length" "16")])
+
 (define_insn "stack_tie"
   [(set (mem:BLK (scratch))
 	(unspec:BLK [(match_operand:DI 0 "register_operand" "rk")
diff --git a/gcc/config/aarch64/constraints.md b/gcc/config/aarch64/constraints.md
index 5b189ea..b09d10d 100644
--- a/gcc/config/aarch64/constraints.md
+++ b/gcc/config/aarch64/constraints.md
@@ -24,6 +24,9 @@
 (define_register_constraint "Ucs" "CALLER_SAVE_REGS"
   "@internal The caller save registers.")
 
+(define_register_constraint "Uc0" "FIXED_REG0"
+  "@internal Represent X0/W0.")
+
 (define_register_constraint "w" "FP_REGS"
   "Floating point and SIMD vector registers.")
 
diff --git a/gcc/testsuite/gcc.target/aarch64/tlsdesc_hoist.c b/gcc/testsuite/gcc.target/aarch64/tlsdesc_hoist.c
new file mode 100644
index 0000000..f9a6d7f
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/tlsdesc_hoist.c
@@ -0,0 +1,21 @@
+/* { dg-do compile } */
+/* { dg-require-effective-target tls_native } */
+/* { dg-options "-O2 -fpic -fdump-rtl-loop2_invariant" } */
+
+int cal (int, int);
+__thread int tls_data;
+
+int
+foo (int bound)
+{
+  int i = 0;
+  int sum = 0;
+
+  for (i; i < bound; i++)
+    sum = cal (sum, tls_data);
+
+  return sum;
+}
+
+/* Insn sequences for TLS descriptor should be hoisted out of the loop.  */
+/* { dg-final { scan-rtl-dump "Decided" "loop2_invariant" } } */