add some notes about pseudos being typeless

Commit Message

Luc Van Oostenryck April 10, 2021, 7:02 p.m. UTC

Pseudos are untyped. It's usually OK because their type can nevertheless
be retrieved in a simple way. But it also complicates things and
worse in some cases the type is completely lost.

Tell a bit more about it in the TODO file.

Signed-off-by: Luc Van Oostenryck <[e-mail]>
---
 Documentation/TODO.md | 9 +++++++++
 1 file changed, 9 insertions(+)

Patch

diff --git a/Documentation/TODO.md b/Documentation/TODO.md
index 3f00bb1104d1..bb25c714a212 100644
--- a/Documentation/TODO.md
+++ b/Documentation/TODO.md
@@ -56,6 +56,15 @@  Optimization
 
 IR
 --
+* pseudos are untyped, it's usually OK but often it complicates things:
+  - PSEUDO_REGs are defined by instructions and their type is normally
+    retrievable via this defining instruction but in some case they're not:
+    for example, pseudos defined by ASM output.
+  - PSEUDO_ARGs are considered as defined by OP_ENTRY and are used like
+    for liveness trackability but their type can't simply be retrieved via
+    this instruction like PSEUDO_REGs are (with ->def->type).
+  - PSEUDO_VALs are completely typeless.
+  Maybe a few bits should be used to store some kind of low-level type.
 * OP_SET should return a bool, always
 * add IR instructions for va_arg() & friends
 * add a possibility to import of file in "IR assembly"