[PATCH] D77396: [LangRef] update text for shufflevector

[Sanjay Patel via Phabricator via llvm-commits]

spatel updated this revision to Diff 255721.
spatel added a comment.

Patch updated:
Restore description of constant mask elements as integer or undef. That seemed redundant to me before, but it's better to state that explicitly, so we don't let weird stuff like constant expressions into the picture.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D77396/new/

https://reviews.llvm.org/D77396

Files:
  llvm/docs/LangRef.rst


Index: llvm/docs/LangRef.rst
===================================================================
--- llvm/docs/LangRef.rst
+++ llvm/docs/LangRef.rst
@@ -8688,27 +8688,27 @@
 """"""""""
 
 The first two operands of a '``shufflevector``' instruction are vectors
-with the same type. The third argument is a shuffle mask whose element
-type is always 'i32'. The result of the instruction is a vector whose
-length is the same as the shuffle mask and whose element type is the
+with the same type. The third argument is a shuffle mask vector constant
+whose element type is ``i32``. The mask vector elements must be constant
+integers or ``undef`` values. The result of the instruction is a vector
+whose length is the same as the shuffle mask and whose element type is the
 same as the element type of the first two operands.
 
-The shuffle mask operand is required to be a constant vector with either
-constant integer or undef values.
-
 Semantics:
 """"""""""
 
 The elements of the two input vectors are numbered from left to right
-across both of the vectors. The shuffle mask operand specifies, for each
-element of the result vector, which element of the two input vectors the
-result element gets.
-
-If the shuffle mask is undef, the result vector is undef. If any element
-of the mask operand is undef, that element of the result is undef. If the
-shuffle mask selects an undef element from one of the input vectors, the
-resulting element is undef. An undef mask element prevents a poisoned
-vector element from propagating.
+across both of the vectors. For each element of the result vector, the
+shuffle mask selects an element from one of the input vectors to copy
+to the result. Non-negative elements in the mask represent an index
+into the concatenated pair of input vectors.
+
+If the shuffle mask is undefined, the result vector is undefined. If
+the shuffle mask selects an undefined element from one of the input
+vectors, the resulting element is undefined. An undefined element
+in the mask vector specifies that the resulting element is undefined.
+An undefined element in the mask vector prevents a poisoned vector
+element from propagating.
 
 For scalable vectors, the only valid mask values at present are
 ``zeroinitializer`` and ``undef``, since we cannot write all indices as


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