diff options
Diffstat (limited to 'content/zettel/3a8a.md')
| -rw-r--r-- | content/zettel/3a8a.md | 25 |
1 files changed, 25 insertions, 0 deletions
diff --git a/content/zettel/3a8a.md b/content/zettel/3a8a.md new file mode 100644 index 0000000..4a51e13 --- /dev/null +++ b/content/zettel/3a8a.md @@ -0,0 +1,25 @@ ++++ +title = "Phi instructions" +author = "Yann Herklotz" +tags = [] +categories = [] +backlinks = ["3a8"] +forwardlinks = ["3a8b", "3a8a1"] +zettelid = "3a8a" ++++ + +One main difference between normal intermediate languages and SSA forms +are phi nodes, which are needed to transform branching statements. By +default, the translation from a non-SSA form to an SSA form can just be +done by labelling each variable with an index, and then each new +assignment to that variable increments the index by one. The last index +is then used by each instruction that uses that variable, which means +that the transformation is semantics preserving. + +However, this is not the case when one can have multiple branches from +multiple locations to a block. In this case, one needs to add phi +instructions to assign the right value to the register. The phi +instructions is defined as a function which returns the argument +according to which predecessor executed the instruction. + +This means that branching instructions can be executed correctly. |