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.
Tested on aarch64-linux-gnu, x86_64-linux-gnu and powerpc64le-linux-gnu.
Also tested by comparing the testsuite assembly output on at least one
target per CPU directory. OK to install?
Richard
2017-09-18 Richard Sandiford <richard.sandif...@linaro.org>
Alan Hayward <alan.hayw...@arm.com>
David Sherwood <david.sherw...@arm.com>
gcc/
* combine.c (can_change_dest_mode): Reject changes in
REGMODE_NATURAL_SIZE.
Index: gcc/combine.c
===================================================================
--- gcc/combine.c 2017-09-18 12:31:05.459555526 +0100
+++ gcc/combine.c 2017-09-18 12:31:05.604645232 +0100
@@ -2451,6 +2451,12 @@ can_change_dest_mode (rtx x, int added_s
if (!REG_P (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. */
