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Author SHA1 Message Date
Roman Lebedev e819f7c9fe
[Codegen] If reasonable, materialize clang's `AssumeAlignedAttr` as llvm's Alignment Attribute on call-site function return value 
Summary:
This should be mostly NFC - we still lower the same alignment
knowledge to the IR. The main reasoning here is that
this somewhat improves readability of IR like this,
and will improve test coverage in upcoming patch.

Even though the alignment is guaranteed to always be an I-C-E,
we don't always materialize it as llvm's Alignment Attribute because:
1. There may be a non-zero offset
2. We may be sanitizing for alignment

Note that if there already was an IR alignment attribute
on return value, we union them, and thus the alignment
only ever rises.

Also, there is a second relevant clang attribute `AllocAlignAttr`,
so that is why `AbstractAssumeAlignedAttrEmitter` is templated.

Reviewers: erichkeane, jdoerfert, hfinkel, aaron.ballman, rsmith

Reviewed By: erichkeane

Subscribers: cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D73005
 2020-01-23 22:50:49 +03:00
Erich Keane f759395994 Reland r374450 with Richard Smith's comments and test fixed. 
The behavior from the original patch has changed, since we're no longer
allowing LLVM to just ignore the alignment.  Instead, we're just
assuming the maximum possible alignment.

Differential Revision: https://reviews.llvm.org/D68824

llvm-svn: 374562
 2019-10-11 14:59:44 +00:00
NAKAMURA Takumi 6ed6ef7ac2 clang/test/CodeGen/builtin-assume-aligned.c: Fix for -Asserts. 
llvm-svn: 218507
 2014-09-26 09:37:15 +00:00
Hal Finkel ee90a223ea Support the assume_aligned function attribute 
In addition to __builtin_assume_aligned, GCC also supports an assume_aligned
attribute which specifies the alignment (and optional offset) of a function's
return value. Here we implement support for the assume_aligned attribute by making
use of the @llvm.assume intrinsic.

llvm-svn: 218500
 2014-09-26 05:04:30 +00:00
NAKAMURA Takumi 4b04c11d00 clang/test/CodeGen/builtin-assume*.c: Fixup for -Asserts. 
llvm-svn: 217352
 2014-09-08 01:12:55 +00:00
Hal Finkel bcc06085a8 Add __builtin_assume and __builtin_assume_aligned using @llvm.assume. 
This makes use of the recently-added @llvm.assume intrinsic to implement a
__builtin_assume(bool) intrinsic (to provide additional information to the
optimizer). This hooks up __assume in MS-compatibility mode to mirror
__builtin_assume (the semantics have been intentionally kept compatible), and
implements GCC's __builtin_assume_aligned as assume((p - o) & mask == 0). LLVM
now contains special logic to deal with assumptions of this form.

llvm-svn: 217349
 2014-09-07 22:58:14 +00:00