aarch64.c (aarch64_legitimize_address): Force register scaling out of memory referenc...

	* config/aarch64/aarch64.c (aarch64_legitimize_address): Force
	register scaling out of memory reference and comment why.

From-SVN: r233136

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 3e2f22a..7646774 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,8 @@
+2016-02-04  Bin Cheng  <bin.cheng@arm.com>
+
+       * config/aarch64/aarch64.c (aarch64_legitimize_address): Force
+       register scaling out of memory reference and comment why.
+
 2016-02-04  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
 
        PR target/65932

diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
index 3ff12ff..7ab5ec8 100644 (file)
--- a/gcc/config/aarch64/aarch64.c
+++ b/gcc/config/aarch64/aarch64.c
@@ -4988,13 +4988,18 @@ aarch64_legitimize_address (rtx x, rtx /* orig_x  */, machine_mode mode)
               Rt = Ra + Rc;
               addr = Rt + Rb<<SCALE.
 
-            Here we split CONST out of memory referece because:
+            TODO: We really should split CONST out of memory referece
+            because:
               a) We depend on GIMPLE optimizers to pick up common sub
                  expression involving the scaling operation.
               b) The index Rb is likely a loop iv, it's better to split
                  the CONST so that computation of new base Rt is a loop
                  invariant and can be moved out of loop.  This is more
-                 important when the original base Ra is sfp related.  */
+                 important when the original base Ra is sfp related.
+
+            Unfortunately, GIMPLE optimizers (e.g., SLSR) can not handle
+            this kind of CSE opportunity at the time of this change, we
+            have to force register scaling expr out of memory ref now.  */
          else if (REG_P (op0) || REG_P (op1))
            {
              machine_mode addr_mode = GET_MODE (x);
@@ -5004,14 +5009,13 @@ aarch64_legitimize_address (rtx x, rtx /* orig_x  */, machine_mode mode)
              if (REG_P (op1))
                std::swap (op0, op1);
 
-             rtx addr = gen_rtx_PLUS (addr_mode, op1, base);
+             rtx addr = plus_constant (addr_mode, base, offset);
 
              if (aarch64_legitimate_address_hook_p (mode, addr, false))
                {
-                 base = force_operand (plus_constant (addr_mode,
-                                                      op0, offset),
+                 base = force_operand (gen_rtx_PLUS (addr_mode, op1, op0),
                                        NULL_RTX);
-                 return gen_rtx_PLUS (addr_mode, op1, base);
+                 return plus_constant (addr_mode, base, offset);
                }
            }
        }