silly assembly for comparing Doubles
A function like f x = if x > 0.0 then ... else ...
compiles to the assembly
movsd 7(%rbx),%xmm0
xorpd %xmm1,%xmm1
ucomisd %xmm1,%xmm0
seta %al
movzbl %al,%eax
cmpq $1,%rax
jb _c1tb
This seta/movzbl/cmpq/jb
is bad, we can just generate ja
(and 7.10 did).
The cause is that the code generator produces Cmm like
switch [0 .. 1] %MO_F_Gt_W64(_s1sv::F64, 0.0 :: W64)::I64 {
case 0 : goto c1tb;
case 1 : goto c1tc;
}
which turns into
if (%MO_F_Gt_W64(_s1sv::F64,
0.0 :: W64) < 1) goto c1tb; else goto c1tc;
and then GHC is stuck. It knows how to turn condition >= 1
into condition
, and it knows how to turn condition < 1
into a negated version of condition
when possible, but there is no negated version of MO_F_Gt_W64
(it's not MO_F_Le_W64
because of NaNs and signed zeros). It doesn't know how to turn a negated conditional into a conditional with the branches swapped because it doesn't look at that much at once.
Presumably more fallout from #10137 (closed), and maybe can be fixed simultaneously with #10677 (closed).
Trac metadata
Trac field | Value |
---|---|
Version | 7.11 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler (CodeGen) |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |