Re-add the feature flag for invpcid, which was removed in r294561.
Add an intrinsic, which always uses a 32 bit integer as first argument,
while the instruction actually uses a 64 bit register in 64 bit mode
for the INVPCID_TYPE argument.
Reviewers: craig.topper
Reviewed By: craig.topper
Differential Revision: https://reviews.llvm.org/D47141
llvm-svn: 333255
This patch aims to match the changes introduced in gcc by
https://gcc.gnu.org/ml/gcc-cvs/2018-04/msg00534.html. The
IBT feature definition is removed, with the IBT instructions
being freely available on all X86 targets. The shadow stack
instructions are also being made freely available, and the
use of all these CET instructions is controlled by the module
flags derived from the -fcf-protection clang option. The hasSHSTK
option remains since clang uses it to determine availability of
shadow stack instruction intrinsics, but it is no longer directly used.
Comes with a clang patch (D46881).
Patch by mike.dvoretsky
Differential Revision: https://reviews.llvm.org/D46882
llvm-svn: 332705
Summary:
and use the -msgx flag as a requirement
for the SGX instructions.
Reviewers: craig.topper, zvi
Reviewed By: craig.topper
Differential Revision: https://reviews.llvm.org/D46436
llvm-svn: 331742
Three new instructions:
umonitor - Sets up a linear address range to be
monitored by hardware and activates the monitor.
The address range should be a writeback memory
caching type.
umwait - A hint that allows the processor to
stop instruction execution and enter an
implementation-dependent optimized state
until occurrence of a class of events.
tpause - Directs the processor to enter an
implementation-dependent optimized state
until the TSC reaches the value in EDX:EAX.
Also modifying the description of the mfence
instruction, as the rep prefix (0xF3) was allowed
before, which would conflict with umonitor during
disassembly.
Before:
$ echo 0xf3,0x0f,0xae,0xf0 | llvm-mc -disassemble
.text
mfence
After:
$ echo 0xf3,0x0f,0xae,0xf0 | llvm-mc -disassemble
.text
umonitor %rax
Reviewers: craig.topper, zvi
Reviewed By: craig.topper
Differential Revision: https://reviews.llvm.org/D45253
llvm-svn: 330462
Using Goldmont's cost tables for these two upcoming
atom archs.
Reviewers: craig.topper
Reviewed By: craig.topper
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D45612
llvm-svn: 330109
Hint to hardware to move the cache line containing the
address to a more distant level of the cache without
writing back to memory.
Reviewers: craig.topper, zvi
Reviewed By: craig.topper
Differential Revision: https://reviews.llvm.org/D45256
llvm-svn: 329992
Similar to the wbinvd instruction, except this
one does not invalidate caches. Ring 0 only.
The encoding matches a wbinvd instruction with
an F3 prefix.
Reviewers: craig.topper, zvi, ashlykov
Reviewed By: craig.topper
Differential Revision: https://reviews.llvm.org/D43816
llvm-svn: 329847
Add fdiv costs for Goldmont using table 16-17 of the Intel Optimization Manual. Also add overrides for FSQRT for Goldmont and Silvermont.
Reviewers: RKSimon
Reviewed By: RKSimon
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D44644
llvm-svn: 328451
Almost none of these usages were FP specific. And we had no clear guideliness on when to use hasAVX vs hasFP256.
I might also remove hasInt256 too since its an alias for hasAVX2.
llvm-svn: 326682
This patch adds a new function attribute "required-vector-width" that can be set by the frontend to indicate the maximum vector width present in the original source code. The idea is that this would be set based on ABI requirements, intrinsics or explicit vector types being used, maybe simd pragmas, etc. The backend will then use this information to determine if its save to make 512-bit vectors illegal when the preference is for 256-bit vectors.
For code that has no vectors in it originally and only get vectors through the loop and slp vectorizers this allows us to generate code largely similar to our AVX2 only output while still enabling AVX512 features like mask registers and gather/scatter. The loop vectorizer doesn't always obey TTI and will create oversized vectors with the expectation the backend will legalize it. In order to avoid changing the vectorizer and potentially harm our AVX2 codegen this patch tries to make the legalizer behavior similar.
This is restricted to CPUs that support AVX512F and AVX512VL so that we have good fallback options to use 128 and 256-bit vectors and still get masking.
I've qualified every place I could find in X86ISelLowering.cpp and added tests cases for many of them with 2 different values for the attribute to see the codegen differences.
We still need to do frontend work for the attribute and teach the inliner how to merge it, etc. But this gets the codegen layer ready for it.
Differential Revision: https://reviews.llvm.org/D42724
llvm-svn: 324834
We currently emit up to 15-byte NOPs on all targets (apart from Silvermont), which stalls performance on some targets with decoders that struggle with 2 or 3 more '66' prefixes.
This patch flags recent AMD targets (btver1/znver1) to still emit 15-byte NOPs and bdver* targets to emit 11-byte NOPs. All other targets now emit 10-byte NOPs apart from SilverMont CPUs which still emit 7-byte NOPS.
Differential Revision: https://reviews.llvm.org/D42616
llvm-svn: 323693
Summary:
First, we need to explain the core of the vulnerability. Note that this
is a very incomplete description, please see the Project Zero blog post
for details:
https://googleprojectzero.blogspot.com/2018/01/reading-privileged-memory-with-side.html
The basis for branch target injection is to direct speculative execution
of the processor to some "gadget" of executable code by poisoning the
prediction of indirect branches with the address of that gadget. The
gadget in turn contains an operation that provides a side channel for
reading data. Most commonly, this will look like a load of secret data
followed by a branch on the loaded value and then a load of some
predictable cache line. The attacker then uses timing of the processors
cache to determine which direction the branch took *in the speculative
execution*, and in turn what one bit of the loaded value was. Due to the
nature of these timing side channels and the branch predictor on Intel
processors, this allows an attacker to leak data only accessible to
a privileged domain (like the kernel) back into an unprivileged domain.
The goal is simple: avoid generating code which contains an indirect
branch that could have its prediction poisoned by an attacker. In many
cases, the compiler can simply use directed conditional branches and
a small search tree. LLVM already has support for lowering switches in
this way and the first step of this patch is to disable jump-table
lowering of switches and introduce a pass to rewrite explicit indirectbr
sequences into a switch over integers.
However, there is no fully general alternative to indirect calls. We
introduce a new construct we call a "retpoline" to implement indirect
calls in a non-speculatable way. It can be thought of loosely as
a trampoline for indirect calls which uses the RET instruction on x86.
Further, we arrange for a specific call->ret sequence which ensures the
processor predicts the return to go to a controlled, known location. The
retpoline then "smashes" the return address pushed onto the stack by the
call with the desired target of the original indirect call. The result
is a predicted return to the next instruction after a call (which can be
used to trap speculative execution within an infinite loop) and an
actual indirect branch to an arbitrary address.
On 64-bit x86 ABIs, this is especially easily done in the compiler by
using a guaranteed scratch register to pass the target into this device.
For 32-bit ABIs there isn't a guaranteed scratch register and so several
different retpoline variants are introduced to use a scratch register if
one is available in the calling convention and to otherwise use direct
stack push/pop sequences to pass the target address.
This "retpoline" mitigation is fully described in the following blog
post: https://support.google.com/faqs/answer/7625886
We also support a target feature that disables emission of the retpoline
thunk by the compiler to allow for custom thunks if users want them.
These are particularly useful in environments like kernels that
routinely do hot-patching on boot and want to hot-patch their thunk to
different code sequences. They can write this custom thunk and use
`-mretpoline-external-thunk` *in addition* to `-mretpoline`. In this
case, on x86-64 thu thunk names must be:
```
__llvm_external_retpoline_r11
```
or on 32-bit:
```
__llvm_external_retpoline_eax
__llvm_external_retpoline_ecx
__llvm_external_retpoline_edx
__llvm_external_retpoline_push
```
And the target of the retpoline is passed in the named register, or in
the case of the `push` suffix on the top of the stack via a `pushl`
instruction.
There is one other important source of indirect branches in x86 ELF
binaries: the PLT. These patches also include support for LLD to
generate PLT entries that perform a retpoline-style indirection.
The only other indirect branches remaining that we are aware of are from
precompiled runtimes (such as crt0.o and similar). The ones we have
found are not really attackable, and so we have not focused on them
here, but eventually these runtimes should also be replicated for
retpoline-ed configurations for completeness.
For kernels or other freestanding or fully static executables, the
compiler switch `-mretpoline` is sufficient to fully mitigate this
particular attack. For dynamic executables, you must compile *all*
libraries with `-mretpoline` and additionally link the dynamic
executable and all shared libraries with LLD and pass `-z retpolineplt`
(or use similar functionality from some other linker). We strongly
recommend also using `-z now` as non-lazy binding allows the
retpoline-mitigated PLT to be substantially smaller.
When manually apply similar transformations to `-mretpoline` to the
Linux kernel we observed very small performance hits to applications
running typical workloads, and relatively minor hits (approximately 2%)
even for extremely syscall-heavy applications. This is largely due to
the small number of indirect branches that occur in performance
sensitive paths of the kernel.
When using these patches on statically linked applications, especially
C++ applications, you should expect to see a much more dramatic
performance hit. For microbenchmarks that are switch, indirect-, or
virtual-call heavy we have seen overheads ranging from 10% to 50%.
However, real-world workloads exhibit substantially lower performance
impact. Notably, techniques such as PGO and ThinLTO dramatically reduce
the impact of hot indirect calls (by speculatively promoting them to
direct calls) and allow optimized search trees to be used to lower
switches. If you need to deploy these techniques in C++ applications, we
*strongly* recommend that you ensure all hot call targets are statically
linked (avoiding PLT indirection) and use both PGO and ThinLTO. Well
tuned servers using all of these techniques saw 5% - 10% overhead from
the use of retpoline.
We will add detailed documentation covering these components in
subsequent patches, but wanted to make the core functionality available
as soon as possible. Happy for more code review, but we'd really like to
get these patches landed and backported ASAP for obvious reasons. We're
planning to backport this to both 6.0 and 5.0 release streams and get
a 5.0 release with just this cherry picked ASAP for distros and vendors.
This patch is the work of a number of people over the past month: Eric, Reid,
Rui, and myself. I'm mailing it out as a single commit due to the time
sensitive nature of landing this and the need to backport it. Huge thanks to
everyone who helped out here, and everyone at Intel who helped out in
discussions about how to craft this. Also, credit goes to Paul Turner (at
Google, but not an LLVM contributor) for much of the underlying retpoline
design.
Reviewers: echristo, rnk, ruiu, craig.topper, DavidKreitzer
Subscribers: sanjoy, emaste, mcrosier, mgorny, mehdi_amini, hiraditya, llvm-commits
Differential Revision: https://reviews.llvm.org/D41723
llvm-svn: 323155
This change applies to places where we would turn 128/256-bit code into 512-bit in order to get a wider element type through sext/zext. Any 512-bit types that already existed in the IR/DAG will be left that way.
The width preference has no effect on codegen behavior when the target does not have AVX512 enabled. So AVX/AVX2 codegen cannot be limited via this mechanism yet.
If the preference is lower than 256 we may still use a 256 bit type to do the operation. Constraining to 128 bits makes it much more difficult to support some operations. For many of these cases we need to change element width while keeping element count constant which is easiest done by switching between 256 and 128 bit.
The preference is only obeyed when AVX512 and VLX are available. This means the preference is not obeyed for KNL, but is obeyed for SKX, Cannonlake, and Icelake. For KNL, the only way to do masked operation is on 512-bit registers so we would have to completely disable masking to obey the preference. We would also lose support for gather, scatter, ctlz, vXi64 multiplies, etc. This may change in the future, but this simplifies the initial implementation.
Differential Revision: https://reviews.llvm.org/D41895
llvm-svn: 323016
This will cause the vectorizers to do some limiting of the vector widths they create. This is not a strict limit. There are reasons I know of that the loop vectorizer will generate larger vectors for.
I've written this in such a way that the interface will only return a properly supported width(0/128/256/512) even if the attribute says something funny like 384 or 10.
This has been split from D41895 with the remainder in a follow up commit.
llvm-svn: 323015
This adds a new instrinsic to support the rdpid instruction. The implementation is a bit weird because the intrinsic is defined as always returning 32-bits, but the assembler support thinks the instruction produces a 64-bit register in 64-bit mode. But really it zeros the upper 32 bits. So I had to add separate patterns where 64-bit mode uses an extract_subreg.
Differential Revision: https://reviews.llvm.org/D42205
llvm-svn: 322910
After D41349, we can no get a MCSubtargetInfo into the MCAsmBackend constructor. This allows us to get NOPL from a subtarget feature rather than a CPU name blacklist.
Differential Revision: https://reviews.llvm.org/D41721
llvm-svn: 322227
Previously prefetch was only considered legal if sse was enabled, but it should be supported with 3dnow as well.
The prfchw flag now imply at least some form of prefetch without the write hint is available, either the sse or 3dnow version. This is true even if 3dnow and sse are explicitly disabled.
Similarly prefetchwt1 feature implies availability of prefetchw and the the prefetcht0/1/2/nta instructions. This way we can support _MM_HINT_ET0 using prefetchw and _MM_HINT_ET1 with prefetchwt1. And its assumed that if we have levels for the write hint we would have levels for the non-write hint, thus why we enable the sse prefetch instructions.
I believe this behavior is consistent with gcc. I've updated the prefetch.ll to test all of these combinations.
llvm-svn: 321335
As mentioned in D38318 and D40865, modern Intel processors prefer to combine multiple shuffles to a variable shuffle mask (PSHUFB/VPERMPS etc.) instead of having multiple stage 'fixed' shuffles which put more pressure on Port 5 (at the expense of extra shuffle mask loads).
This patch provides a FeatureFastVariableShuffle target flag for Haswell+ CPUs that prefers combining 2 or more fixed shuffles to a single variable shuffle (default is 3 shuffles).
The long term aim is to drive more of this from schedule data (probably via the MC) but we're not close to being ready for that yet.
Differential Revision: https://reviews.llvm.org/D41323
llvm-svn: 321074
Note:
- X86ISelLowering: setLibcallName(SINCOS) was superfluous as
InitLibcalls() already does it.
- ARMISelLowering: Setting libcallnames for sincos/sincosf seemed
superfluous as in the darwin case it wouldn't be used while for all
other cases InitLibcalls already does it.
llvm-svn: 321036
Shadow stack solution introduces a new stack for return addresses only.
The HW has a Shadow Stack Pointer (SSP) that points to the next return address.
If we return to a different address, an exception is triggered.
The shadow stack is managed using a series of intrinsics that are introduced in this patch as well as the new register (SSP).
The intrinsics are mapped to new instruction set that implements CET mechanism.
The patch also includes initial infrastructure support for IBT.
For more information, please see the following:
https://software.intel.com/sites/default/files/managed/4d/2a/control-flow-enforcement-technology-preview.pdf
Differential Revision: https://reviews.llvm.org/D40223
Change-Id: I4daa1f27e88176be79a4ac3b4cd26a459e88fed4
llvm-svn: 318996
Summary:
These instructions zero the non-scalar part of the lower 128-bits which makes them different than the FMA3 instructions which pass through the non-scalar part of the lower 128-bits.
I've only added fmadd because we should be able to derive all other variants using operand negation in the intrinsic header like we do for AVX512.
I think there are still some missed negate folding opportunities with the FMA4 instructions in light of this behavior difference that I hadn't noticed before.
I've split the tests so that we can use different intrinsics for scalar testing between the two. I just copied the tests split the RUN lines and changed out the scalar intrinsics.
fma4-fneg-combine.ll is a new test to make sure we negate the fma4 intrinsics correctly though there are a couple TODOs in it.
Reviewers: RKSimon, spatel
Reviewed By: RKSimon
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D39851
llvm-svn: 318984
Summary:
This adds a new fast gather feature bit to cover all CPUs that support fast gather that we can use independent of whether the AVX512 feature is enabled. I'm only using this new bit to qualify AVX2 codegen. AVX512 is still implicitly assuming fast gather to keep tests working and to match the scatter behavior.
Test command lines have been added for these two cases.
Reviewers: magabari, delena, RKSimon, zvi
Reviewed By: RKSimon
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D40282
llvm-svn: 318983
All these headers already depend on CodeGen headers so moving them into
CodeGen fixes the layering (since CodeGen depends on Target, not the
other way around).
llvm-svn: 318490
Previously our VEX patterns were checking Subtarget.hasFMA() which checked FMA || AVX512. So we were behaving as if AVX512 implied it anyway. Which means we'd allow VEX encoded 128/256 FMA when AVX512F was enabled but AVX512VL is off. Regardless of the FMA flag.
EVEX to VEX also transforms scalar EVEX FMA instructions to their VEX versions even without the FMA flag. Similarly for 128/256 under AVX512VL.
So this makes AVX512 imply FeatureFMA to make our current behavior explicit.
All known CPUs that support AVX512 have VEX FMA instructions.
llvm-svn: 317520
This fixes bugzilla 26810
https://bugs.llvm.org/show_bug.cgi?id=26810
This is intended to prevent sequences like:
movl %ebp, 8(%esp) # 4-byte Spill
movl %ecx, %ebp
movl %ebx, %ecx
movl %edi, %ebx
movl %edx, %edi
cltd
idivl %esi
movl %edi, %edx
movl %ebx, %edi
movl %ecx, %ebx
movl %ebp, %ecx
movl 16(%esp), %ebp # 4 - byte Reload
Such sequences are created in 2 scenarios:
Scenario #1:
vreg0 is evicted from physreg0 by vreg1
Evictee vreg0 is intended for region splitting with split candidate physreg0 (the reg vreg0 was evicted from)
Region splitting creates a local interval because of interference with the evictor vreg1 (normally region spliiting creates 2 interval, the "by reg" and "by stack" intervals. Local interval created when interference occurs.)
one of the split intervals ends up evicting vreg2 from physreg1
Evictee vreg2 is intended for region splitting with split candidate physreg1
one of the split intervals ends up evicting vreg3 from physreg2 etc.. until someone spills
Scenario #2
vreg0 is evicted from physreg0 by vreg1
vreg2 is evicted from physreg2 by vreg3 etc
Evictee vreg0 is intended for region splitting with split candidate physreg1
Region splitting creates a local interval because of interference with the evictor vreg1
one of the split intervals ends up evicting back original evictor vreg1 from physreg0 (the reg vreg0 was evicted from)
Another evictee vreg2 is intended for region splitting with split candidate physreg1
one of the split intervals ends up evicting vreg3 from physreg2 etc.. until someone spills
As compile time was a concern, I've added a flag to control weather we do cost calculations for local intervals we expect to be created (it's on by default for X86 target, off for the rest).
Differential Revision: https://reviews.llvm.org/D35816
Change-Id: Id9411ff7bbb845463d289ba2ae97737a1ee7cc39
llvm-svn: 316295
Turns out we have no patterns on the instructions that were using this feature flag for other reasons. These instructions are slow on all modern CPUs so it seems unlikely that we will spend any effort supporting these instructions going forward. So we might as well just kill of the feature flag and just fix up the comments.
llvm-svn: 315862
Summary:
This adds a set of new directives that describe 32-bit x86 prologues.
The directives are limited and do not expose the full complexity of
codeview FPO data. They are merely a convenience for the compiler to
generate more readable assembly so we don't need to generate tons of
labels in CodeGen. If our prologue emission changes in the future, we
can change the set of available directives to suit our needs. These are
modelled after the .seh_ directives, which use a different format that
interacts with exception handling.
The directives are:
.cv_fpo_proc _foo
.cv_fpo_pushreg ebp/ebx/etc
.cv_fpo_setframe ebp/esi/etc
.cv_fpo_stackalloc 200
.cv_fpo_endprologue
.cv_fpo_endproc
.cv_fpo_data _foo
I tried to follow the implementation of ARM EHABI CFI directives by
sinking most directives out of MCStreamer and into X86TargetStreamer.
This helps avoid polluting non-X86 code with WinCOFF specific logic.
I used cdb to confirm that this can show locals in parent CSRs in a few
cases, most importantly the one where we use ESI as a frame pointer,
i.e. the one in http://crbug.com/756153#c28
Once we have cdb integration in debuginfo-tests, we can add integration
tests there.
Reviewers: majnemer, hans
Subscribers: aemerson, mgorny, kristof.beyls, llvm-commits, hiraditya
Differential Revision: https://reviews.llvm.org/D38776
llvm-svn: 315513
The Swift CC is identical to Win64 CC with the exception of swift error
being passed in r12 which is a CSR. However, since this calling
convention is only used in swift -> swift code, it does not impact
interoperability and can be treated entirely as Win64 CC. We would
previously incorrectly lower the frame setup as we did not treat the
frame as conforming to Win64 specifications.
llvm-svn: 313813
Adding x86 Processor families to initialize several uArch properties (based on the family)
This patch shows how gather cost can be initialized based on the proc. family
Differential Revision: https://reviews.llvm.org/D35348
llvm-svn: 313132
Summary:
Currently we determine if macro fusion is supported based on the AVX flag as a proxy for the processor being Sandy Bridge".
This is really strange as now AMD supports AVX. It also means if user explicitly disables AVX we disable macro fusion.
This patch adds an explicit macro fusion feature. I've also enabled for the generic 64-bit CPU (which doesn't have AVX)
This is probably another candidate for being in the MI layer, but for now I at least wanted to correct the overloading of the AVX feature.
Reviewers: spatel, chandlerc, RKSimon, zvi
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D37280
llvm-svn: 312097
We don't have an intrinsic implemented for this instruction yet, but it looked odd that we were missing the accessor method from the subtarget.
llvm-svn: 312064
Gabor Buella