[PATCH] rs6000: Disable -fcaller-saves by default

[Pat Haugen <pthaugen@linux.ibm.com>]

Disable -fcaller-saves by default.

This patch turns off -fcaller-saves by default so that IRA doesn't try
to use volatile regs for pseudos that are live across a call, which
would then require LRA to save/restore the reg around the call.

Bootstrap/regtest on powerpc64le with no new regressions. Also ran a
CPU2017 benchmark comparison with no major differences (a few minor
improvements and one minor degradation). Ok for trunk?

-Pat


2020-07-23  Pat Haugen  <pthaugen@linux.ibm.com>

gcc/
	* common/config/rs6000/rs6000-common.c
	(rs6000_option_optimization_table): Turn off -fcaller-saves.

gcc/testsuite/
	* gcc.target/powerpc/caller-saves.c: New.



diff --git a/gcc/common/config/rs6000/rs6000-common.c
b/gcc/common/config/rs6000/rs6000-common.c
index ee37b9dc90b..6d68834aed2 100644
--- a/gcc/common/config/rs6000/rs6000-common.c
+++ b/gcc/common/config/rs6000/rs6000-common.c
@@ -43,8 +43,13 @@ static const struct default_options
rs6000_option_optimization_table[] =
        on rs6000, turn it off by default.  */
     { OPT_LEVELS_ALL, OPT_frename_registers, NULL, 0 },

+    /* Don't allow IRA to use volatile regs across function calls.  */
+    { OPT_LEVELS_ALL, OPT_fcaller_saves, NULL, 0 },
+
     /* Double growth factor to counter reduced min jump length.  */
     { OPT_LEVELS_ALL, OPT__param_max_grow_copy_bb_insns_, NULL, 16 },
+
+    /* Following marks the end of the list and needs to remain last.  */
     { OPT_LEVELS_NONE, 0, NULL, 0 }
   };

diff --git a/gcc/testsuite/gcc.target/powerpc/caller-saves.c
b/gcc/testsuite/gcc.target/powerpc/caller-saves.c
new file mode 100644
index 00000000000..846356f16f7
--- /dev/null
+++ b/gcc/testsuite/gcc.target/powerpc/caller-saves.c
@@ -0,0 +1,9 @@
+/* { dg-do compile */
+/* { dg-options "-O2 -fverbose-asm" } */
+
+void
+foo ()
+{
+}
+
+/* { dg-final { scan-assembler-not "fcaller-saves" } } */