[PATCH] D83119: [Alignment][NFC] Use 5 bits to store Instructions Alignment

[Guillaume Chatelet via Phabricator via llvm-commits]

gchatelet created this revision.
gchatelet added a reviewer: courbet.
Herald added subscribers: llvm-commits, jfb, hiraditya.
Herald added a project: LLVM.
gchatelet edited the summary of this revision.
gchatelet updated this revision to Diff 275322.
gchatelet added a comment.
courbet accepted this revision.
This revision is now accepted and ready to land.

- Remove assert and move implementation in header


courbet added a comment.

Cool ! Only minor comments.



================
Comment at: llvm/include/llvm/IR/Instruction.h:61
+  template <unsigned Offset>
+  using BitfieldAlignmentElement =
+      typename Bitfield::Element<unsigned, Offset, 5,
----------------
[bikeshedding] Shouldn't that be `AlignmentBitfieldElement` ?


================
Comment at: llvm/include/llvm/IR/Instruction.h:59
+  // Template alias so that all Instruction storing alignment use the same
+  // definiton.
+  template <unsigned Offset>
----------------
Add comment:  `// Align(1) is stored as 0. Valid alignments are powers of two from 2^0 to 2^MaxAlignmentExponent = 2^29, so we need 5 bits to encode the 30 possible values.`


As per MaxAlignmentExponent <https://github.com/llvm/llvm-project/blob/b7338fb1a6a464472850211165391983d2c8fdf3/llvm/include/llvm/IR/Value.h#L688> alignment is not allowed to be more than 2^29.
Encoded as Log2, this means that storing alignment uses 5 bits.
This patch makes sure all instructions store their alignment in a consistent way, encoded as Log2 and using 5 bits.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D83119

Files:
  llvm/include/llvm/IR/Instruction.h
  llvm/include/llvm/IR/Instructions.h
  llvm/lib/IR/Instructions.cpp

-------------- next part --------------
A non-text attachment was scrubbed...
Name: D83119.275322.patch
Type: text/x-patch
Size: 5725 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20200703/8372753d/attachment.bin>