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[AArch64] Tighten address register subreg checks

Previously we allowed subregs of non-GPR modes to be base and index
registers in non-strict mode.  In practice such subregs will always
require a reload, so we get better code by disallowing them.

Tested on aarch64-linux-gnu.  OK to install?


2017-08-22  Richard Sandiford  <>
	    Alan Hayward  <>
	    David Sherwood  <>

	* config/aarch64/aarch64.c (aarch64_base_register_rtx_p): Only allow
	subregs whose inner modes can be stored in GPRs.
	(aarch64_classify_index): Likewise.

Index: gcc/config/aarch64/aarch64.c
--- gcc/config/aarch64/aarch64.c	2017-08-22 10:12:29.280432708 +0100
+++ gcc/config/aarch64/aarch64.c	2017-08-22 10:13:53.032828125 +0100
@@ -4196,7 +4196,9 @@ aarch64_regno_ok_for_base_p (int regno,
 static bool
 aarch64_base_register_rtx_p (rtx x, bool strict_p)
-  if (!strict_p && GET_CODE (x) == SUBREG)
+  if (!strict_p
+      && GET_CODE (x) == SUBREG
+      && contains_reg_of_mode[GENERAL_REGS][GET_MODE (SUBREG_REG (x))])
     x = SUBREG_REG (x);
   return (REG_P (x) && aarch64_regno_ok_for_base_p (REGNO (x), strict_p));
@@ -4343,7 +4345,9 @@ aarch64_classify_index (struct aarch64_a
     return false;
-  if (GET_CODE (index) == SUBREG)
+  if (!strict_p
+      && GET_CODE (index) == SUBREG
+      && contains_reg_of_mode[GENERAL_REGS][GET_MODE (SUBREG_REG (index))])
     index = SUBREG_REG (index);
   if ((shift == 0 ||

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