emitCmmLitSwitch could be better
This is a spin off #10124. While looking at the code generated for
f :: Int -> Bool
f a = case a of
1 -> True
2 -> True
3 -> True
4 -> True
8 -> True
9 -> True
11 -> True
19 -> True
_ -> False
I noticed this Cmm:
c2tI:
if (%MO_S_Lt_W64(_s2sJ::I64, 3)) goto c2tw; else goto c2tx;
c2tw:
if (%MO_S_Lt_W64(_s2sJ::I64, 2)) goto c2tq; else goto c2tr;
c2tq:
if (_s2sJ::I64 != 1) goto c2tg; else goto c2th;
c2tr:
if (_s2sJ::I64 != 2) goto c2tg; else goto c2th;
Note that when c2tr
is reached, we know 2 ≤ _s2sJ < 3, so _s2sJ already is 2, and this check is redundant.
emitCmmLitSwitch
does not take that into account, probably because it also needs to work for floats.
I wonder if it isn’t a bit shady to use an if-then-else tree for floats. Maybe for float types, a sequence of equality tests is more suitable. For all other cases, the code generator could make use of "2 ≤ x < 3 ⇒ x = 2" and skip one check.
Trac metadata
Trac field | Value |
---|---|
Version | 7.8.4 |
Type | Task |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler (CodeGen) |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | simonmar |
Operating system | |
Architecture |