[PATCH] x86: Disable jump tables when retpolines are used (PR target/86952).

[Martin Liška]

Hi.

Thanks to Intel guys, we've done some re-measurement in PR86952
about usage of jump tables when retpolines are used.
Numbers prove that disabling of JT should be the best for now.

Patch can bootstrap on x86_64-linux-gnu and survives regression tests.

Ready to be installed?
Thanks,
Martin

gcc/ChangeLog:

2019-03-06  Martin Liska  <mli...@suse.cz>

        PR target/86952
        * config/i386/i386.c (ix86_option_override_internal): Disable
        jump tables when retpolines are used.

gcc/testsuite/ChangeLog:

2019-03-06  Martin Liska  <mli...@suse.cz>

        PR target/86952
        * gcc.target/i386/pr86952.c: New test.
        * gcc.target/i386/indirect-thunk-7.c: Use jump tables to match
        scanned pattern.
        * gcc.target/i386/indirect-thunk-inline-7.c: Likewise.
---
 gcc/config/i386/i386.c                        |  4 ++++
 .../gcc.target/i386/indirect-thunk-7.c        |  2 +-
 .../gcc.target/i386/indirect-thunk-inline-7.c |  2 +-
 gcc/testsuite/gcc.target/i386/pr86952.c       | 23 +++++++++++++++++++
 4 files changed, 29 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/gcc.target/i386/pr86952.c



diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
index c8f9957163b..37fe41260dd 100644
--- a/gcc/config/i386/i386.c
+++ b/gcc/config/i386/i386.c
@@ -4894,6 +4894,10 @@ ix86_option_override_internal (bool main_args_p,
 			   opts->x_param_values,
 			   opts_set->x_param_values);
 
+  if (ix86_indirect_branch != indirect_branch_keep
+      && !opts_set->x_flag_jump_tables)
+    opts->x_flag_jump_tables = 0;
+
   return true;
 }
 
diff --git a/gcc/testsuite/gcc.target/i386/indirect-thunk-7.c b/gcc/testsuite/gcc.target/i386/indirect-thunk-7.c
index 3c72036dbaf..53868f46558 100644
--- a/gcc/testsuite/gcc.target/i386/indirect-thunk-7.c
+++ b/gcc/testsuite/gcc.target/i386/indirect-thunk-7.c
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O2 -mno-indirect-branch-register -mfunction-return=keep -mindirect-branch=thunk -fno-pic" } */
+/* { dg-options "-O2 -mno-indirect-branch-register -mfunction-return=keep -mindirect-branch=thunk -fno-pic -fjump-tables" } */
 
 void func0 (void);
 void func1 (void);
diff --git a/gcc/testsuite/gcc.target/i386/indirect-thunk-inline-7.c b/gcc/testsuite/gcc.target/i386/indirect-thunk-inline-7.c
index ea009245a58..e6f064959a1 100644
--- a/gcc/testsuite/gcc.target/i386/indirect-thunk-inline-7.c
+++ b/gcc/testsuite/gcc.target/i386/indirect-thunk-inline-7.c
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O2 -mno-indirect-branch-register -mfunction-return=keep -mindirect-branch=thunk-inline -fno-pic" } */
+/* { dg-options "-O2 -mno-indirect-branch-register -mfunction-return=keep -mindirect-branch=thunk-inline -fno-pic -fjump-tables" } */
 
 void func0 (void);
 void func1 (void);
diff --git a/gcc/testsuite/gcc.target/i386/pr86952.c b/gcc/testsuite/gcc.target/i386/pr86952.c
new file mode 100644
index 00000000000..3ff3e354878
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr86952.c
@@ -0,0 +1,23 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -mindirect-branch=thunk -fdump-tree-switchlower1" } */
+
+int global;
+
+int 
+foo (int x)
+{
+  switch (x & 7)
+    {
+      case 0: ; return 1722;
+      case 1: global += 1; return 1060;
+      case 2: ; return 1990;
+      case 3: ; return 1242;
+      case 4: ; return 1466;
+      case 5: ; return 894;
+      case 6: ; return 570;
+      case 7: ; return 572;
+      default: return 0;
+    }
+}
+
+/* { dg-final { scan-tree-dump ";; GIMPLE switch case clusters: 1 2 3 4 5 6 7" "switchlower1" } } */