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| -rw-r--r-- | docs/LangRef.html | 26 |
1 files changed, 12 insertions, 14 deletions
diff --git a/docs/LangRef.html b/docs/LangRef.html index 68f1aea..5eb91fe 100644 --- a/docs/LangRef.html +++ b/docs/LangRef.html @@ -2512,10 +2512,9 @@ b: unreachable <div> <p>Poison values are similar to <a href="#undefvalues">undef values</a>, however - instead of representing an unspecified bit pattern, they represent the - fact that an instruction or constant expression which cannot evoke side - effects has nevertheless detected a condition which results in undefined - behavior.</p> + they also represent the fact that an instruction or constant expression which + cannot evoke side effects has nevertheless detected a condition which results + in undefined behavior.</p> <p>There is currently no way of representing a poison value in the IR; they only exist when produced by operations such as @@ -2572,22 +2571,21 @@ b: unreachable </ul> -<p>Whenever a poison value is generated, all values which depend on it evaluate - to poison. If they have side effects, they evoke their side effects as if each - operand with a poison value were undef. If they have externally-visible side - effects, the behavior is undefined.</p> +<p>Poison Values have the same behavior as <a href="#undefvalues">undef values</a>, + with the additional affect that any instruction which has a <i>dependence</i> + on a poison value has undefined behavior.</p> <p>Here are some examples:</p> <pre class="doc_code"> entry: %poison = sub nuw i32 0, 1 ; Results in a poison value. - %still_poison = and i32 %poison, 0 ; Whereas (and i32 undef, 0) would return 0. + %still_poison = and i32 %poison, 0 ; 0, but also poison. %poison_yet_again = getelementptr i32* @h, i32 %still_poison - store i32 0, i32* %poison_yet_again ; undefined behavior + store i32 0, i32* %poison_yet_again ; memory at @h[0] is poisoned - store i32 %poison, i32* @g ; Poison value conceptually stored to memory. - %poison2 = load i32* @g ; Returns a poison value, not just undef. + store i32 %poison, i32* @g ; Poison value stored to memory. + %poison2 = load i32* @g ; Poison value loaded back from memory. store volatile i32 %poison, i32* @g ; External observation; undefined behavior. @@ -2626,8 +2624,8 @@ second_end: store volatile i32 0, i32* @g ; This time, the instruction always depends ; on the store in %end. Also, it is ; control-equivalent to %end, so this is - ; well-defined (again, ignoring earlier - ; undefined behavior in this example). + ; well-defined (ignoring earlier undefined + ; behavior in this example). </pre> </div> |