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| author | Chandler Carruth <chandlerc@gmail.com> | 2011-12-12 04:36:04 +0000 |
|---|---|---|
| committer | Chandler Carruth <chandlerc@gmail.com> | 2011-12-12 04:36:04 +0000 |
| commit | 48b0bbf930f9efa72f46f70b7e81dec69c2397cc (patch) | |
| tree | a4bcaa71b1c61f5abebbd64c96b319788cfaf616 | |
| parent | c4eab904c95549106f628b6fdd8ccf62527aa398 (diff) | |
Update the LangRef documentation for llvm.ctlz and llvm.cttz to specify
the behavior with the newly added flag for undefined results on a zero
input.
I'm terrible at documentation, so comments and suggestions welcome here.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@146361 91177308-0d34-0410-b5e6-96231b3b80d8
| -rw-r--r-- | docs/LangRef.html | 60 |
1 files changed, 37 insertions, 23 deletions
diff --git a/docs/LangRef.html b/docs/LangRef.html index 2d77ca48ee..b4751e8189 100644 --- a/docs/LangRef.html +++ b/docs/LangRef.html @@ -7335,12 +7335,12 @@ LLVM</a>.</p> targets support all bit widths or vector types, however.</p> <pre> - declare i8 @llvm.ctlz.i8 (i8 <src>) - declare i16 @llvm.ctlz.i16(i16 <src>) - declare i32 @llvm.ctlz.i32(i32 <src>) - declare i64 @llvm.ctlz.i64(i64 <src>) - declare i256 @llvm.ctlz.i256(i256 <src>) - declare <2 x i32> @llvm.ctlz.v2i32(<2 x i32> <src;gt) + declare i8 @llvm.ctlz.i8 (i8 <src>, i1 <is_zero_undef>) + declare i16 @llvm.ctlz.i16 (i16 <src>, i1 <is_zero_undef>) + declare i32 @llvm.ctlz.i32 (i32 <src>, i1 <is_zero_undef>) + declare i64 @llvm.ctlz.i64 (i64 <src>, i1 <is_zero_undef>) + declare i256 @llvm.ctlz.i256(i256 <src>, i1 <is_zero_undef>) + declase <2 x i32> @llvm.ctlz.v2i32(<2 x i32> <src>, i1 <is_zero_undef>) </pre> <h5>Overview:</h5> @@ -7348,15 +7348,22 @@ LLVM</a>.</p> leading zeros in a variable.</p> <h5>Arguments:</h5> -<p>The only argument is the value to be counted. The argument may be of any - integer type, or any vector type with integer element type. - The return type must match the argument type.</p> +<p>The first argument is the value to be counted. This argument may be of any + integer type, or a vectory with integer element type. The return type + must match the first argument type.</p> + +<p>The second argument must be a constant and is a flag to indicate whether the + intrinsic should ensure that a zero as the first argument produces a defined + result. Historically some architectures did not provide a defined result for + zero values as efficiently, and many algorithms are now predicated on + avoiding zero-value inputs.</p> <h5>Semantics:</h5> <p>The '<tt>llvm.ctlz</tt>' intrinsic counts the leading (most significant) - zeros in a variable, or within each element of the vector if the operation - is of vector type. If the src == 0 then the result is the size in bits of - the type of src. For example, <tt>llvm.ctlz(i32 2) = 30</tt>.</p> + zeros in a variable, or within each element of the vector. + If <tt>src == 0</tt> then the result is the size in bits of the type of + <tt>src</tt> if <tt>is_zero_undef == 0</tt> and <tt>undef</tt> otherwise. + For example, <tt>llvm.ctlz(i32 2) = 30</tt>.</p> </div> @@ -7373,12 +7380,12 @@ LLVM</a>.</p> support all bit widths or vector types, however.</p> <pre> - declare i8 @llvm.cttz.i8 (i8 <src>) - declare i16 @llvm.cttz.i16(i16 <src>) - declare i32 @llvm.cttz.i32(i32 <src>) - declare i64 @llvm.cttz.i64(i64 <src>) - declare i256 @llvm.cttz.i256(i256 <src>) - declase <2 x i32> @llvm.cttz.v2i32(<2 x i32> <src>) + declare i8 @llvm.cttz.i8 (i8 <src>, i1 <is_zero_undef>) + declare i16 @llvm.cttz.i16 (i16 <src>, i1 <is_zero_undef>) + declare i32 @llvm.cttz.i32 (i32 <src>, i1 <is_zero_undef>) + declare i64 @llvm.cttz.i64 (i64 <src>, i1 <is_zero_undef>) + declare i256 @llvm.cttz.i256(i256 <src>, i1 <is_zero_undef>) + declase <2 x i32> @llvm.cttz.v2i32(<2 x i32> <src>, i1 <is_zero_undef>) </pre> <h5>Overview:</h5> @@ -7386,15 +7393,22 @@ LLVM</a>.</p> trailing zeros.</p> <h5>Arguments:</h5> -<p>The only argument is the value to be counted. The argument may be of any - integer type, or a vectory with integer element type.. The return type - must match the argument type.</p> +<p>The first argument is the value to be counted. This argument may be of any + integer type, or a vectory with integer element type. The return type + must match the first argument type.</p> + +<p>The second argument must be a constant and is a flag to indicate whether the + intrinsic should ensure that a zero as the first argument produces a defined + result. Historically some architectures did not provide a defined result for + zero values as efficiently, and many algorithms are now predicated on + avoiding zero-value inputs.</p> <h5>Semantics:</h5> <p>The '<tt>llvm.cttz</tt>' intrinsic counts the trailing (least significant) zeros in a variable, or within each element of a vector. - If the src == 0 then the result is the size in bits of - the type of src. For example, <tt>llvm.cttz(2) = 1</tt>.</p> + If <tt>src == 0</tt> then the result is the size in bits of the type of + <tt>src</tt> if <tt>is_zero_undef == 0</tt> and <tt>undef</tt> otherwise. + For example, <tt>llvm.cttz(2) = 1</tt>.</p> </div> |