Prevent invalid register mode changes in combine

This patch stops combine from changing the mode of an existing register
in-place if doing so would change the size of the underlying register
allocation size, as given by REGMODE_NATURAL_SIZE.  Without this,
many tests fail in adjust_reg_mode after SVE is added.  One example
is gcc.c-torture/compile/20090401-1.c.

2017-11-01  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* combine.c (can_change_dest_mode): Reject changes in
	REGMODE_NATURAL_SIZE.

Co-Authored-By: Alan Hayward <alan.hayward@arm.com>
Co-Authored-By: David Sherwood <david.sherwood@arm.com>
From-SVN: r254291

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 4c653194a4c8cb0711d839d536ec4dd15b80e6ad..1886218f7b59a064db20c9d53b2a43382c09a535 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,10 @@
+2017-11-01  Richard Sandiford  <richard.sandiford@linaro.org>
+           Alan Hayward  <alan.hayward@arm.com>
+           David Sherwood  <david.sherwood@arm.com>
+
+       * combine.c (can_change_dest_mode): Reject changes in
+       REGMODE_NATURAL_SIZE.
+
 2017-10-31  Sandra Loosemore  <sandra@codesourcery.com>
 
        * configure.ac (--enable-libssp): New.

diff --git a/gcc/combine.c b/gcc/combine.c
index 93adfc11be749fba7fecc9b06cf72c57553dbdf2..4afae213a3f129ebb4980ac3a2380a4bdeb76ade 100644 (file)
--- a/gcc/combine.c
+++ b/gcc/combine.c
@@ -2478,6 +2478,12 @@ can_change_dest_mode (rtx x, int added_sets, machine_mode mode)
       != REGMODE_NATURAL_SIZE (GET_MODE (x)))
     return false;
 
+  /* Don't change between modes with different underlying register sizes,
+     since this could lead to invalid subregs.  */
+  if (REGMODE_NATURAL_SIZE (mode)
+      != REGMODE_NATURAL_SIZE (GET_MODE (x)))
+    return false;
+
   regno = REGNO (x);
   /* Allow hard registers if the new mode is legal, and occupies no more
      registers than the old mode.  */