x86: Disable jump tables when retpolines are used (PR target/86952).
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State New
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  • x86: Disable jump tables when retpolines are used (PR target/86952).
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Commit Message

Martin Liška March 7, 2019, 8:45 a.m. UTC
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  <mliska@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  <mliska@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

Comments

Uros Bizjak March 7, 2019, 8:54 a.m. UTC | #1
On Thu, Mar 7, 2019 at 9:45 AM Martin Liška <mliska@suse.cz> wrote:
>
> 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

Please add a comment above your change.

Uros.

>
> gcc/ChangeLog:
>
> 2019-03-06  Martin Liska  <mliska@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  <mliska@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
>
>
Martin Liška March 7, 2019, 9:50 a.m. UTC | #2
On 3/7/19 9:54 AM, Uros Bizjak wrote:
> On Thu, Mar 7, 2019 at 9:45 AM Martin Liška <mliska@suse.cz> wrote:
>>
>> 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
> 
> Please add a comment above your change.

Sure, should be improved.

Martin

> 
> Uros.
> 
>>
>> gcc/ChangeLog:
>>
>> 2019-03-06  Martin Liska  <mliska@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  <mliska@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
>>
>>
From 54a0f3ed784c05bef0bdddcc6ae4e8677307d989 Mon Sep 17 00:00:00 2001
From: marxin <mliska@suse.cz>
Date: Wed, 6 Mar 2019 13:05:50 +0100
Subject: [PATCH] x86: Disable jump tables when retpolines are used (PR
 target/86952).

Jump tables are implement on x86_64 with:
	jmp	*.L4(,%rdi,8)

where L4 contains list of labels where to jump. When using retpolines,
the instruction is replaced with:
	movq	.L4(,%rdi,8), %rax
	jmp	*%rax

which bypasses/confuses indirect branch predictor and it's slow. In that
case, a decision tree based on if condition is faster.

gcc/ChangeLog:

2019-03-06  Martin Liska  <mliska@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  <mliska@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" } } */
Uros Bizjak March 7, 2019, 10:27 a.m. UTC | #3
On Thu, Mar 7, 2019 at 10:50 AM Martin Liška <mliska@suse.cz> wrote:
>
> On 3/7/19 9:54 AM, Uros Bizjak wrote:
> > On Thu, Mar 7, 2019 at 9:45 AM Martin Liška <mliska@suse.cz> wrote:
> >>
> >> 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
> >
> > Please add a comment above your change.
>
> Sure, should be improved.

Eh, we didn't understand each other... Please add comment here:

+  if (ix86_indirect_branch != indirect_branch_keep
+      && !opts_set->x_flag_jump_tables)
+    opts->x_flag_jump_tables = 0;

so in future, it will still be documented why this part of the code is needed.

Uros.

> Martin
>
> >
> > Uros.
> >
> >>
> >> gcc/ChangeLog:
> >>
> >> 2019-03-06  Martin Liska  <mliska@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  <mliska@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
> >>
> >>
>
Martin Liška March 7, 2019, 10:41 a.m. UTC | #4
On 3/7/19 11:27 AM, Uros Bizjak wrote:
> On Thu, Mar 7, 2019 at 10:50 AM Martin Liška <mliska@suse.cz> wrote:
>>
>> On 3/7/19 9:54 AM, Uros Bizjak wrote:
>>> On Thu, Mar 7, 2019 at 9:45 AM Martin Liška <mliska@suse.cz> wrote:
>>>>
>>>> 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
>>>
>>> Please add a comment above your change.
>>
>> Sure, should be improved.
> 
> Eh, we didn't understand each other... Please add comment here:

Ah, this place :)

> 
> +  if (ix86_indirect_branch != indirect_branch_keep
> +      && !opts_set->x_flag_jump_tables)
> +    opts->x_flag_jump_tables = 0;
> 
> so in future, it will still be documented why this part of the code is needed.

Sure, updated.

Martin

> 
> Uros.
> 
>> Martin
>>
>>>
>>> Uros.
>>>
>>>>
>>>> gcc/ChangeLog:
>>>>
>>>> 2019-03-06  Martin Liska  <mliska@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  <mliska@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
>>>>
>>>>
>>
From f78914272ba7a9fd19db65876a4d4cab576ddf0f Mon Sep 17 00:00:00 2001
From: marxin <mliska@suse.cz>
Date: Wed, 6 Mar 2019 13:05:50 +0100
Subject: [PATCH] x86: Disable jump tables when retpolines are used (PR
 target/86952).

Jump tables are implement on x86_64 with:
	jmp	*.L4(,%rdi,8)

where L4 contains list of labels where to jump. When using retpolines,
the instruction is replaced with:
	movq	.L4(,%rdi,8), %rax
	jmp	*%rax

which bypasses/confuses indirect branch predictor and it's slow. In that
case, a decision tree based on if condition is faster.

gcc/ChangeLog:

2019-03-06  Martin Liska  <mliska@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  <mliska@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                        |  6 +++++
 .../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, 31 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..71e5cfd2897 100644
--- a/gcc/config/i386/i386.c
+++ b/gcc/config/i386/i386.c
@@ -4894,6 +4894,12 @@ ix86_option_override_internal (bool main_args_p,
 			   opts->x_param_values,
 			   opts_set->x_param_values);
 
+  /* PR86952: jump table usage with retpolines is slow.
+     The PR provides some numbers about the slowness.  */
+  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" } } */
Jan Hubicka March 8, 2019, 12:44 p.m. UTC | #5
> 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?

OK, thanks!
I wonder if there is some threshold for extremely large jumptables where
branchy sequence will loose, but I think it is better to disable them
than what we have right now.

Honza
Martin Liška March 8, 2019, 1:50 p.m. UTC | #6
On 3/8/19 1:44 PM, Jan Hubicka wrote:
>> 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?
> 
> OK, thanks!
> I wonder if there is some threshold for extremely large jumptables where
> branchy sequence will loose, but I think it is better to disable them
> than what we have right now.

I tested switch statements up to 4096 and it was still slower ;)

Martin

> 
> Honza
>
Jan Hubicka March 8, 2019, 1:58 p.m. UTC | #7
> On 3/8/19 1:44 PM, Jan Hubicka wrote:
> >> 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?
> > 
> > OK, thanks!
> > I wonder if there is some threshold for extremely large jumptables where
> > branchy sequence will loose, but I think it is better to disable them
> > than what we have right now.
> 
> I tested switch statements up to 4096 and it was still slower ;)

Well, we have switch statements with this many cases in
insn-attrtab/latencytab tables.  I suppose what kind of code you compile
with retpolines, but I would expect even bigger switch statements to
appear in real code (large DFA automatons and such)

Honza
> 
> Martin
> 
> > 
> > Honza
> > 
>
Martin Liška March 8, 2019, 2:15 p.m. UTC | #8
On 3/8/19 2:58 PM, Jan Hubicka wrote:
>> On 3/8/19 1:44 PM, Jan Hubicka wrote:
>>>> 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?
>>>
>>> OK, thanks!
>>> I wonder if there is some threshold for extremely large jumptables where
>>> branchy sequence will loose, but I think it is better to disable them
>>> than what we have right now.
>>
>> I tested switch statements up to 4096 and it was still slower ;)
> 
> Well, we have switch statements with this many cases in
> insn-attrtab/latencytab tables.  I suppose what kind of code you compile
> with retpolines, but I would expect even bigger switch statements to
> appear in real code (large DFA automatons and such)

Question is whether you'll meet such huge switch statements in Linux kernel?

Martin

> 
> Honza
>>
>> Martin
>>
>>>
>>> Honza
>>>
>>
Jakub Jelinek March 8, 2019, 2:19 p.m. UTC | #9
On Fri, Mar 08, 2019 at 02:50:26PM +0100, Martin Liška wrote:
> On 3/8/19 1:44 PM, Jan Hubicka wrote:
> >> 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?
> > 
> > OK, thanks!
> > I wonder if there is some threshold for extremely large jumptables where
> > branchy sequence will loose, but I think it is better to disable them
> > than what we have right now.
> 
> I tested switch statements up to 4096 and it was still slower ;)

Try one with 10000000 of entries ;) and also compare code size and data
segment size.

	Jakub

Patch
diff mbox series

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" } } */