From 9f926f3a0c8dee7edb6807323a1fe2a92b33bfaa Mon Sep 17 00:00:00 2001 From: Alexander Monakov Date: Wed, 24 May 2023 15:48:29 +0300 Subject: [PATCH] doc: clarify semantics of vector bitwise shifts Explicitly say that attempted shift past element bit width is UB for vector types. Mention that integer promotions do not happen. gcc/ChangeLog: * doc/extend.texi (Vector Extensions): Clarify bitwise shift semantics. --- gcc/doc/extend.texi | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi index f9d13b495ad..cdbd4b34a35 100644 --- a/gcc/doc/extend.texi +++ b/gcc/doc/extend.texi @@ -12026,7 +12026,14 @@ elements in the operand. It is possible to use shifting operators @code{<<}, @code{>>} on integer-type vectors. The operation is defined as following: @code{@{a0, a1, @dots{}, an@} >> @{b0, b1, @dots{}, bn@} == @{a0 >> b0, a1 >> b1, -@dots{}, an >> bn@}}@. Vector operands must have the same number of +@dots{}, an >> bn@}}@. Unlike OpenCL, values of @code{b} are not +implicitly taken modulo bit width of the base type @code{B}, and the behavior +is undefined if any @code{bi} is greater than or equal to @code{B}. + +In contrast to scalar operations in C and C++, operands of integer vector +operations do not undergo integer promotions. + +Operands of binary vector operations must have the same number of elements. For convenience, it is allowed to use a binary vector operation