1587 Commits

Author SHA1 Message Date
Alexey Bataev
4e3d4622b1 Fix undefined behaviour when trying to deref nullptr. 2020-06-04 17:52:06 -04:00
Alexey Bataev
bd1c03d7b7 [OPENMP50]Codegen for inscan reductions in worksharing directives.
Summary:
Implemented codegen for reduction clauses with inscan modifiers in
worksharing constructs.

Emits the code for the directive with inscan reductions.
The code is the following:
```
size num_iters = <num_iters>;
<type> buffer[num_iters];
for (i: 0..<num_iters>) {
  <input phase>;
  buffer[i] = red;
}
for (int k = 0; k != ceil(log2(num_iters)); ++k)
for (size cnt = last_iter; cnt >= pow(2, k); --k)
  buffer[i] op= buffer[i-pow(2,k)];
for (0..<num_iters>) {
  red = InclusiveScan ? buffer[i] : buffer[i-1];
  <scan phase>;
}
```

Reviewers: jdoerfert

Subscribers: yaxunl, guansong, arphaman, cfe-commits, caomhin

Tags: #clang

Differential Revision: https://reviews.llvm.org/D79948
2020-06-04 16:29:33 -04:00
John McCall
8a8d703be0 Fix how cc1 command line options are mapped into FP options.
Canonicalize on storing FP options in LangOptions instead of
redundantly in CodeGenOptions.  Incorporate -ffast-math directly
into the values of those LangOptions rather than considering it
separately when building FPOptions.  Build IR attributes from
those options rather than a mix of sources.

We should really simplify the driver/cc1 interaction here and have
the driver pass down options that cc1 directly honors.  That can
happen in a follow-up, though.

Patch by Michele Scandale!
https://reviews.llvm.org/D80315
2020-06-01 22:00:30 -04:00
Florian Hahn
8f3f88d2f5 [Matrix] Implement matrix index expressions ([][]).
This patch implements matrix index expressions
(matrix[RowIdx][ColumnIdx]).

It does so by introducing a new MatrixSubscriptExpr(Base, RowIdx, ColumnIdx).
MatrixSubscriptExprs are built in 2 steps in ActOnMatrixSubscriptExpr. First,
if the base of a subscript is of matrix type, we create a incomplete
MatrixSubscriptExpr(base, idx, nullptr). Second, if the base is an incomplete
MatrixSubscriptExpr, we create a complete
MatrixSubscriptExpr(base->getBase(), base->getRowIdx(), idx)

Similar to vector elements, it is not possible to take the address of
a MatrixSubscriptExpr.
For CodeGen, a new MatrixElt type is added to LValue, which is very
similar to VectorElt. The only difference is that we may need to cast
the type of the base from an array to a vector type when accessing it.

Reviewers: rjmccall, anemet, Bigcheese, rsmith, martong

Reviewed By: rjmccall

Differential Revision: https://reviews.llvm.org/D76791
2020-06-01 20:08:49 +01:00
Zequan Wu
e36076ee3a [clang] Add nomerge function attribute to clang
Differential Revision: https://reviews.llvm.org/D79121
2020-05-21 17:07:39 -07:00
Zequan Wu
b0a0f01bc1 Revert "Add nomerge function attribute to clang"
This reverts commit 307e85395485e1eff9533b2d7952b16f33ceae38.
2020-05-21 16:13:18 -07:00
Zequan Wu
307e853954 Add nomerge function attribute to clang 2020-05-21 15:28:27 -07:00
Eli Friedman
62f3ef2b53 [CGCall] Annotate references with "align" attribute.
If we're going to assume references are dereferenceable, we should also
assume they're aligned: otherwise, we can't actually dereference them.

See also D80072.

Differential Revision: https://reviews.llvm.org/D80166
2020-05-19 20:21:30 -07:00
Sander de Smalen
d6936be2ef [SveEmitter] Add builtins for svdup and svindex
Reviewed By: efriedma

Differential Revision: https://reviews.llvm.org/D79357
2020-05-12 11:02:32 +01:00
Sander de Smalen
4cad97595f [SveEmitter] Add builtins for svmovlb and svmovlt
These builtins are expanded in CGBuiltin to use intrinsics
for (signed/unsigned) shift left long top/bottom.

Reviewers: efriedma, SjoerdMeijer

Reviewed By: efriedma

Differential Revision: https://reviews.llvm.org/D79579
2020-05-11 09:41:58 +01:00
Sander de Smalen
3cb8b4c193 [SveEmitter] Add builtins for SVE2 Polynomial arithmetic
This patch adds builtins for:
- sveorbt
- sveortb
- svpmul
- svpmullb, svpmullb_pair
- svpmullt, svpmullt_pair

The svpmullb and svpmullt builtins are expressed using the svpmullb_pair
and svpmullt_pair LLVM IR intrinsics, respectively.

Reviewers: SjoerdMeijer, efriedma, rengolin

Reviewed By: efriedma

Differential Revision: https://reviews.llvm.org/D79480
2020-05-07 11:53:04 +01:00
Michael Liao
276c8dde0b [clang][codegen] Refactor argument loading in function prolog. NFC.
Summary:
- Skip copying function arguments and unnecessary casting by using them
  directly.

Reviewers: rjmccall, kerbowa, yaxunl

Subscribers: cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D79394
2020-05-05 15:31:51 -04:00
Sander de Smalen
aed6bd6f42 Reland D78750: [SveEmitter] Add builtins for svdupq and svdupq_lane
Edit: Changed a few CHECK lines into CHECK-DAG lines.

This reverts commit 90f3f62cb087782fe2608e95d686c29067281b6e.
2020-05-05 10:42:11 +01:00
Sander de Smalen
90f3f62cb0 Revert "[SveEmitter] Add builtins for svdupq and svdupq_lane"
It seems this patch broke some buildbots, so reverting until I
have had a chance to investigate.

This reverts commit 6b90a6887d25e3375bb916a3ed09f7ccec819d0c.
2020-05-04 21:31:55 +01:00
Sander de Smalen
6b90a6887d [SveEmitter] Add builtins for svdupq and svdupq_lane
* svdupq builtins that duplicate scalars to every quadword of a vector
  are defined using builtins for svld1rq (load and replicate quadword).
* svdupq builtins that duplicate boolean values to fill a predicate vector
  are defined using `svcmpne`.

Reviewers: SjoerdMeijer, efriedma, ctetreau

Reviewed By: efriedma

Tags: #clang

Differential Revision: https://reviews.llvm.org/D78750
2020-05-04 20:38:47 +01:00
Melanie Blower
f5360d4bb3 Reapply "Add support for #pragma float_control" with buildbot fixes
Add support for #pragma float_control

Reviewers: rjmccall, erichkeane, sepavloff

Differential Revision: https://reviews.llvm.org/D72841

This reverts commit fce82c0ed310174fe48e2402ac731b6340098389.
2020-05-04 05:51:25 -07:00
Melanie Blower
fce82c0ed3 Revert "Reapply "Add support for #pragma float_control" with improvements to"
This reverts commit 69aacaf699922ffe0450f567e21208c10c84731f.
2020-05-01 10:31:09 -07:00
Melanie Blower
69aacaf699 Reapply "Add support for #pragma float_control" with improvements to
test cases
Add support for #pragma float_control

Reviewers: rjmccall, erichkeane, sepavloff

Differential Revision: https://reviews.llvm.org/D72841

This reverts commit 85dc033caccaa6ab919d57f9759290be41240146, and makes
corrections to the test cases that failed on buildbots.
2020-05-01 10:03:30 -07:00
Melanie Blower
85dc033cac Revert "Add support for #pragma float_control"
This reverts commit 4f1e9a17e9d28bdfd035313c96b3a5d4c91a7733.
due to fail on buildbot, sorry for the noise
2020-05-01 06:36:58 -07:00
Melanie Blower
4f1e9a17e9 Add support for #pragma float_control
Reviewers: rjmccall, erichkeane, sepavloff

Differential Revision: https://reviews.llvm.org/D72841
2020-05-01 06:14:24 -07:00
Sander de Smalen
42a56bf63f [SveEmitter] Add builtins for gather prefetches
Patch by Andrzej Warzynski

Reviewed By: efriedma

Tags: #clang

Differential Revision: https://reviews.llvm.org/D78677
2020-04-29 11:52:49 +01:00
Christopher Tetreault
ef3678cfee [SVE] Update EmitSVEPredicateCast to take a ScalableVectorType
Summary:
Removes usage of VectorType::getNumElements identified by test located
at CodeGen/aarch64-sve-intrinsics/acle_sve_abs.c. Since the type is an
SVE predicate vector, it makes sense to specialize the code for scalable
vectors only.

Reviewers: rengolin, efriedma

Reviewed By: efriedma

Subscribers: tschuett, kristof.beyls, rkruppe, psnobl, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D78958
2020-04-28 11:22:20 -07:00
Momchil Velikov
102b4105e3 [CMSE] Clear padding bits of struct/unions/fp16 passed by value
When passing a value of a struct/union type from secure to non-secure
state (that is returning from a CMSE entry function or passing an
argument to CMSE-non-secure call), there is a potential sensitive
information leak via the padding bits in the structure. It is not
possible in the general case to ensure those bits are cleared by using
Standard C/C++.

This patch makes the compiler emit code to clear such padding
bits. Since type information is lost in LLVM IR, the code generation
is done by Clang.

For each interesting record type, we build a bitmask, in which all the
bits, corresponding to user declared members, are set. Values of
record types are returned by coercing them to an integer. After the
coercion, the coerced value is masked (with bitwise AND) and then
returned by the function. In a similar manner, values of record types
are passed as arguments by coercing them to an array of integers, and
the coerced values themselves are masked.

For union types, we effectively clear only bits, which aren't part of
any member, since we don't know which is the currently active one.
The compiler will issue a warning, whenever a union is passed to
non-secure state.

Values of half-precision floating-point types are passed in the least
significant bits of a 32-bit register (GPR or FPR) with the most
significant bits unspecified. Since this is also a potential leak of
sensitive information, this patch also clears those unspecified bits.

Differential Revision: https://reviews.llvm.org/D76369
2020-04-28 17:05:58 +01:00
Christopher Tetreault
da8918f27e [SVE][NFC] Use ScalableVectorType in CGBuiltin
Summary: * Upgrade some usages of VectorType to use ScalableVectorType

Reviewers: efriedma, david-arm, fpetrogalli, kmclaughlin

Reviewed By: efriedma

Subscribers: tschuett, rkruppe, psnobl, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D78842
2020-04-27 16:29:45 -07:00
Sander de Smalen
823e2a670a [SveEmitter] Add builtins for contiguous prefetches
This patch also adds the enum `sv_prfop` for the prefetch operation specifier
and checks to ensure the passed enum values are valid.

Reviewers: SjoerdMeijer, efriedma, ctetreau

Reviewed By: efriedma

Tags: #clang

Differential Revision: https://reviews.llvm.org/D78674
2020-04-24 11:35:59 +01:00
Sander de Smalen
2d1baf606a [SveEmitter] Add builtins for svwhilerw/svwhilewr
This also adds the IsOverloadWhileRW flag which tells CGBuiltin to use
the result predicate type and the first pointer type as the
overloaded types for the LLVM IR intrinsic.

Reviewers: SjoerdMeijer, efriedma

Reviewed By: efriedma

Tags: #clang

Differential Revision: https://reviews.llvm.org/D78238
2020-04-22 21:49:18 +01:00
Sander de Smalen
662cbaf647 [SveEmitter] Add IsOverloadNone flag and builtins for svpfalse and svcnt[bhwd]_pat
Add the IsOverloadNone flag to tell CGBuiltin that it does not have
an overloaded type. This is used for e.g. svpfalse which does
not take any arguments and always returns a svbool_t.

This patch also adds builtins for svcntb_pat, svcnth_pat, svcntw_pat
and svcntd_pat, as those don't require custom codegen.

Reviewers: SjoerdMeijer, efriedma, rovka

Reviewed By: efriedma

Tags: #clang

Differential Revision: https://reviews.llvm.org/D77596
2020-04-22 16:42:08 +01:00
Sander de Smalen
41d52662d5 [SveEmitter] Add support for _n form builtins
The ACLE has builtins that take a scalar value that is to be expanded
into a vector by the operation. While the ISA may have an instruction
that takes an immediate or a scalar to represent this, the LLVM IR
intrinsic may not, so Clang will have to splat the scalar value.

This patch also adds the _n forms for svabd, svadd, svdiv, svdivr,
svmax, svmin, svmul, svmulh, svub and svsubr.

Reviewers: SjoerdMeijer, efriedma, rovka

Reviewed By: SjoerdMeijer

Tags: #clang

Differential Revision: https://reviews.llvm.org/D77594
2020-04-22 14:23:54 +01:00
Andrzej Warzynski
72f565899d [SveEmitter] Implement builtins for gathers/scatters
This patch adds builtins for:
  * regular, first-faulting and non-temporal gather loads
  * regular and non-temporal scatter stores

Differential Revision: https://reviews.llvm.org/D77735
2020-04-22 13:21:39 +01:00
Sander de Smalen
c8a5b30bac [SveEmitter] Add range checks for immediates and predicate patterns.
Summary:
This patch adds a mechanism to easily add range checks for a builtin's
immediate operands. This patch is tested with the qdech intrinsic, which takes
both an enum for the predicate pattern, as well as an immediate for the
multiplier.

Reviewers: efriedma, SjoerdMeijer, rovka

Reviewed By: efriedma, SjoerdMeijer

Subscribers: mgorny, tschuett, mgrang, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D76678
2020-04-14 16:49:32 +01:00
Sander de Smalen
17a68c61a9 [SveEmitter] Implement builtins for contiguous loads/stores
This adds builtins for all contiguous loads/stores, including
non-temporal, first-faulting and non-faulting.

Reviewers: efriedma, SjoerdMeijer

Reviewed By: SjoerdMeijer

Tags: #clang

Differential Revision: https://reviews.llvm.org/D76238
2020-04-14 15:24:57 +01:00
Lucas Prates
f56550cf7f [ARM] Enabling range checks on Neon intrinsics' lane arguments
Summary:
Range checks were not properly performed in the lane arguments of Neon
intrinsics implemented based on splat operations. Calls to those
intrinsics where translated to `__builtin__shufflevector` calls directly
by the pre-processor through the arm_neon.h macros, missing the chance
for the proper range checks.

This patch enables the range check by introducing an auxiliary splat
instruction in arm_neon.td, delaying the translation to shufflevector
calls to CGBuiltin.cpp in clang after the checks were performed.

Reviewers: jmolloy, t.p.northover, rsmith, olista01, ostannard

Reviewed By: ostannard

Subscribers: ostannard, dnsampaio, danielkiss, kristof.beyls, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D74619
2020-03-19 12:07:23 +00:00
Lucas Prates
7bf23563f4 Revert "[ARM] Setting missing isLaneQ attribute on Neon Intrisics definitions"
This reverts commit 62ab15ffa3f910c36758e99324deac12ee006c90.

Multiple commits were unintentionally squashed into this one. Reverting
so each of them can be pushed properly.
2020-03-19 12:01:13 +00:00
Lucas Prates
62ab15ffa3 [ARM] Setting missing isLaneQ attribute on Neon Intrisics definitions
Summary:
Some of the `*_laneq` intrinsics defined in arm_neon.td were missing the
setting of the `isLaneQ` attribute. This patch sets the attribute on the
related definitions, as they will be required to properly perform range
checks on their lane arguments.

Reviewers: jmolloy, t.p.northover, rsmith, olista01, dnsampaio

Reviewed By: dnsampaio

Subscribers: dnsampaio, kristof.beyls, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D74616
2020-03-19 11:52:41 +00:00
Sander de Smalen
c5b81466c2 Reland D75470 [SVE] Auto-generate builtins and header for svld1.
Reworked the patch to avoid sharing a header (SVETypeFlags.h) between
include/clang/Basic and utils/TableGen/SveEmitter.cpp. Now the patch
generates the enum/flags which is included in TargetBuiltins.h.

Also renamed one of the SveEmitter options to be in line with MVE.

Summary:

This is a first patch in a series for the SveEmitter to generate the arm_sve.h
header file and builtins.

I've tried my best to strip down this patch as best as I could, but there
are still a few changes that are not necessarily exercised by the load intrinsics
in this patch, mostly around the SVEType class which has some common logic to
represent types from a type and prototype string. I thought it didn't make
much sense to remove that from this patch and split it up.
2020-03-18 11:16:28 +00:00
Sander de Smalen
6ce537ccfc Revert "[SVE] Auto-generate builtins and header for svld1."
This reverts commit 8b409eabaf755c88a7d652fe99d3ad858a4fe82a.

Reverting this patch for now because it breaks some buildbots.
2020-03-16 15:22:15 +00:00
Sander de Smalen
8b409eabaf [SVE] Auto-generate builtins and header for svld1.
This is a first patch in a series for the SveEmitter to generate the arm_sve.h
header file and builtins.

I've tried my best to strip down this patch as best as I could, but there
are still a few changes that are not necessarily exercised by the load intrinsics
in this patch, mostly around the SVEType class which has some common logic to
represent types from a type and prototype string. I thought it didn't make
much sense to remove that from this patch and split it up.

Reviewers: efriedma, rovka, SjoerdMeijer, rsandifo-arm, rengolin

Reviewed By: SjoerdMeijer

Tags: #clang

Differential Revision: https://reviews.llvm.org/D75470
2020-03-16 10:52:37 +00:00
Sander de Smalen
5087ace651 [Clang][SVE] Parse builtin type string for scalable vectors
This patch adds 'q' to mean 'scalable vector' in the builtin
type string, and for SVE will return the matching builtin
type as defined in the C/C++ language extensions for SVE.

This patch also adds some scaffolding to generate the arm_sve.h
header file, and some builtin definitions (+CodeGen) to be able
to implement some simple masked load intrinsics that use the
ACLE types, such as:

 svint8_t test_svld1_s8(svbool_t pg, const int8_t *base) {
   return svld1_s8(pg, base);
 }

Reviewers: efriedma, rjmccall, rovka, rsandifo-arm, rengolin

Reviewed By: efriedma

Tags: #clang

Differential Revision: https://reviews.llvm.org/D75298
2020-03-15 14:34:52 +00:00
Mikhail Maltsev
47edf5bafb [ARM,CDE] Generalize MVE intrinsics infrastructure to support CDE
Summary:
This patch generalizes the existing code to support CDE intrinsics
which will share some properties with existing MVE intrinsics
(some of the intrinsics will be polymorphic and accept/return values
of MVE vector types).
Specifically the patch:
* Adds new tablegen backends -gen-arm-cde-builtin-def,
  -gen-arm-cde-builtin-codegen, -gen-arm-cde-builtin-sema,
  -gen-arm-cde-builtin-aliases, -gen-arm-cde-builtin-header based on
  existing MVE backends.
* Renames the '__clang_arm_mve_alias' attribute into
  '__clang_arm_builtin_alias' (it will be used with CDE intrinsics as
  well as MVE intrinsics)
* Implements semantic checks for the coprocessor argument of the CDE
  intrinsics as well as the existing coprocessor intrinsics.
* Adds one CDE intrinsic __arm_cx1 to test the above changes

Reviewers: simon_tatham, MarkMurrayARM, ostannard, dmgreen

Reviewed By: simon_tatham

Subscribers: sdesmalen, mgorny, kristof.beyls, danielkiss, cfe-commits, llvm-commits

Tags: #clang, #llvm

Differential Revision: https://reviews.llvm.org/D75850
2020-03-10 14:03:16 +00:00
Alexey Bataev
c112e941a0 [OPENMP50]Add basic support for depobj construct.
Added basic parsing/sema/serialization support for depobj directive.
2020-03-02 13:10:32 -05:00
Vedant Kumar
c54597b99d [ubsan] Add support for -fsanitize=nullability-* suppressions
rdar://59402904
2020-02-28 14:30:40 -08:00
Fady Ghanim
ba3f863dfb [OpenMP][OMPIRBuilder] Introducing the OMPBuilderCBHelpers helper class
This patch introduces a new helper class `OMPBuilderCBHelpers`,
which will contain all reusable C/C++ language specific function-
alities required by the `OMPIRBuilder`.

Initially, this helper class contains the body and finalization
codegen functionalities implemented using callbacks which were
moved here for reusability among the different directives
implemented in the `OMPIRBuilder`, along with RAIIs for preserving
state prior to emitting outlined and/or inlined OpenMP regions.

In the future this helper class will also contain all the different
call backs required by OpenMP clauses/variable privatization.

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D74562
2020-02-19 14:11:17 -06:00
Fangrui Song
1d49eb00d9 [AsmPrinter] De-capitalize all AsmPrinter::Emit* but EmitInstruction
Similar to rL328848.
2020-02-13 17:06:24 -08:00
Michael Liao
a067891389 [clang][codegen] Fix another lifetime emission on alloca on non-default address space.
- Lifetime intrinsics expect the pointer directly from alloca. Need
  extra handling for targets with alloca on non-default (or non-zero)
  address space.
2020-02-10 00:15:56 -05:00
Guillaume Chatelet
07c9d53266 [Alignment][NFC] Use Align with CreateAlignedLoad
Summary:
This is patch is part of a series to introduce an Alignment type.
See this thread for context: http://lists.llvm.org/pipermail/llvm-dev/2019-July/133851.html
See this patch for the introduction of the type: https://reviews.llvm.org/D64790

Reviewers: courbet, bollu

Subscribers: hiraditya, cfe-commits, llvm-commits

Tags: #clang, #llvm

Differential Revision: https://reviews.llvm.org/D73449
2020-01-27 10:58:36 +01:00
Diogo Sampaio
2147703bde Revert "[ARM] Follow AACPS standard for volatile bit-fields access width"
This reverts commit 6a24339a45246b66bd3de88cc9c6a5b5e77c0645.
Submitted using ide button by mistake
2020-01-21 15:31:33 +00:00
Diogo Sampaio
6a24339a45 [ARM] Follow AACPS standard for volatile bit-fields access width
Summary:
This patch resumes the work of D16586.
According to the AAPCS, volatile bit-fields should
be accessed using containers of the widht of their
declarative type. In such case:
```
struct S1 {
  short a : 1;
}
```
should be accessed using load and stores of the width
(sizeof(short)), where now the compiler does only load
the minimum required width (char in this case).
However, as discussed in D16586,
that could overwrite non-volatile bit-fields, which
conflicted with C and C++ object models by creating
data race conditions that are not part of the bit-field,
e.g.
```
struct S2 {
  short a;
  int  b : 16;
}
```
Accessing `S2.b` would also access `S2.a`.

The AAPCS Release 2019Q1.1
(https://static.docs.arm.com/ihi0042/g/aapcs32.pdf)
section 8.1 Data Types, page 35, "Volatile bit-fields -
preserving number and width of container accesses" has been
updated to avoid conflict with the C++ Memory Model.
Now it reads in the note:
```
This ABI does not place any restrictions on the access widths
of bit-fields where the container overlaps with a non-bit-field member.
 This is because the C/C++ memory model defines these as being separate
memory locations, which can be accessed by two threads
 simultaneously. For this reason, compilers must be permitted to use a
narrower memory access width (including splitting the access
 into multiple instructions) to avoid writing to a different memory location.
```

I've updated the patch D16586 to follow such behavior by verifying that we
only change volatile bit-field access when:
 - it won't overlap with any other non-bit-field member
 - we only access memory inside the bounds of the record

Regarding the number of memory accesses, that should be preserved, that will
be implemented by D67399.

Reviewers: rsmith, rjmccall, eli.friedman, ostannard

Subscribers: ostannard, kristof.beyls, cfe-commits, carwil, olista01

Tags: #clang

Differential Revision: https://reviews.llvm.org/D72932
2020-01-21 15:23:38 +00:00
Alexey Bataev
c33ba8c158 [OPENMP]Improve debug locations in OpenMP regions.
Emit more precise debug locations for the OpenMP outlined regions.
2020-01-17 14:24:32 -05:00
Sameer Sahasrabuddhe
ed181efa17 [HIP][AMDGPU] expand printf when compiling HIP to AMDGPU
Summary:
This change implements the expansion in two parts:
- Add a utility function emitAMDGPUPrintfCall() in LLVM.
- Invoke the above function from Clang CodeGen, when processing a HIP
  program for the AMDGPU target.

The printf expansion has undefined behaviour if the format string is
not a compile-time constant. As a sufficient condition, the HIP
ToolChain now emits -Werror=format-nonliteral.

Reviewed By: arsenm

Differential Revision: https://reviews.llvm.org/D71365
2020-01-16 15:15:38 +05:30
Alex Richardson
8c387cbea7 Add builtins for aligning and checking alignment of pointers and integers
This change introduces three new builtins (which work on both pointers
and integers) that can be used instead of common bitwise arithmetic:
__builtin_align_up(x, alignment), __builtin_align_down(x, alignment) and
__builtin_is_aligned(x, alignment).

I originally added these builtins to the CHERI fork of LLVM a few years ago
to handle the slightly different C semantics that we use for CHERI [1].
Until recently these builtins (or sequences of other builtins) were
required to generate correct code. I have since made changes to the default
C semantics so that they are no longer strictly necessary (but using them
does generate slightly more efficient code). However, based on our experience
using them in various projects over the past few years, I believe that adding
these builtins to clang would be useful.

These builtins have the following benefit over bit-manipulation and casts
via uintptr_t:

- The named builtins clearly convey the semantics of the operation. While
  checking alignment using __builtin_is_aligned(x, 16) versus
  ((x & 15) == 0) is probably not a huge win in readably, I personally find
  __builtin_align_up(x, N) a lot easier to read than (x+(N-1))&~(N-1).
- They preserve the type of the argument (including const qualifiers). When
  using casts via uintptr_t, it is easy to cast to the wrong type or strip
  qualifiers such as const.
- If the alignment argument is a constant value, clang can check that it is
  a power-of-two and within the range of the type. Since the semantics of
  these builtins is well defined compared to arbitrary bit-manipulation,
  it is possible to add a UBSAN checker that the run-time value is a valid
  power-of-two. I intend to add this as a follow-up to this change.
- The builtins avoids int-to-pointer casts both in C and LLVM IR.
  In the future (i.e. once most optimizations handle it), we could use the new
  llvm.ptrmask intrinsic to avoid the ptrtoint instruction that would normally
  be generated.
- They can be used to round up/down to the next aligned value for both
  integers and pointers without requiring two separate macros.
- In many projects the alignment operations are already wrapped in macros (e.g.
  roundup2 and rounddown2 in FreeBSD), so by replacing the macro implementation
  with a builtin call, we get improved diagnostics for many call-sites while
  only having to change a few lines.
- Finally, the builtins also emit assume_aligned metadata when used on pointers.
  This can improve code generation compared to the uintptr_t casts.

[1] In our CHERI compiler we have compilation mode where all pointers are
implemented as capabilities (essentially unforgeable 128-bit fat pointers).
In our original model, casts from uintptr_t (which is a 128-bit capability)
to an integer value returned the "offset" of the capability (i.e. the
difference between the virtual address and the base of the allocation).
This causes problems for cases such as checking the alignment: for example, the
expression `if ((uintptr_t)ptr & 63) == 0` is generally used to check if the
pointer is aligned to a multiple of 64 bytes. The problem with offsets is that
any pointer to the beginning of an allocation will have an offset of zero, so
this check always succeeds in that case (even if the address is not correctly
aligned). The same issues also exist when aligning up or down. Using the
alignment builtins ensures that the address is used instead of the offset. While
I have since changed the default C semantics to return the address instead of
the offset when casting, this offset compilation mode can still be used by
passing a command-line flag.

Reviewers: rsmith, aaron.ballman, theraven, fhahn, lebedev.ri, nlopes, aqjune
Reviewed By: aaron.ballman, lebedev.ri
Differential Revision: https://reviews.llvm.org/D71499
2020-01-09 21:48:29 +00:00