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| author | Dan Gohman <gohman@apple.com> | 2011-04-12 23:05:59 +0000 |
|---|---|---|
| committer | Dan Gohman <gohman@apple.com> | 2011-04-12 23:05:59 +0000 |
| commit | c8454ee9954e9257bd82428b415b64000a02a62a (patch) | |
| tree | c897f272e61468fbb8389318f37ef385c6cc08ac /llvm/docs/LangRef.html | |
| parent | dbfde42468221dffae736513ca68853e798ae018 (diff) | |
| download | bcm5719-llvm-c8454ee9954e9257bd82428b415b64000a02a62a.tar.gz bcm5719-llvm-c8454ee9954e9257bd82428b415b64000a02a62a.zip | |
Fix a hole in the definition of "dependence" used by trap values. Trap
values are also transmitted through branches which cause side effects to
be skipped altogether.
llvm-svn: 129404
Diffstat (limited to 'llvm/docs/LangRef.html')
| -rw-r--r-- | llvm/docs/LangRef.html | 24 |
1 files changed, 22 insertions, 2 deletions
diff --git a/llvm/docs/LangRef.html b/llvm/docs/LangRef.html index 90b200809c3..dfb0bd1d7e9 100644 --- a/llvm/docs/LangRef.html +++ b/llvm/docs/LangRef.html @@ -2371,6 +2371,11 @@ b: unreachable is always executed when control transfers to one of the successors, and may not be executed when control is transfered to another.</li> +<li>Additionally, an instruction also <i>control-depends</i> on a terminator + instruction if the set of instructions it otherwise depends on would be + different if the terminator had transfered control to a different + successor.</li> + <li>Dependence is transitive.</li> </ul> @@ -2413,8 +2418,23 @@ end: ; control-dependent on %cmp, so this ; always results in a trap value. - volatile store i32 0, i32* @g ; %end is control-equivalent to %entry - ; so this is defined (ignoring earlier + volatile store i32 0, i32* @g ; This would depend on the store in %true + ; if %cmp is true, or the store in %entry + ; otherwise, so this is undefined behavior. + + %br i1 %cmp, %second_true, %second_end + ; The same branch again, but this time the + ; true block doesn't have side effects. + +second_true: + ; No side effects! + br label %end + +second_end: + volatile store 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). </pre> |
