Using single register class in Pat conversion in XXXInstrInfo.td

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#1

Hello LLVMDevs,

I have following two patterns :

def : Pat<(selectcc (f32 GR32:$L), (f32 GR32:$R),
(i32 GR32:$T), (i32 GR32:$F), SETOLT),
(Select_CC GR32:$T, GR32:$F, (FCMP_LT GR32:$L, GR32:$R), 1)>;
def : Pat<(selectcc (f32 GR32:$L), (f32 GR32:$R),
(f32 GR32:$T), (f32 GR32:$F), SETOLT),
(Select_CC GR32:$T, GR32:$F, (FCMP_LT GR32:$L, GR32:$R), 1)>;

but I want to write it to single pattern like

Pat<(selectcc (f32 GR32:$L), (f32 GR32:$R),
GR32:$T, GR32:$F, SETOLT),
(Select_CC GR32:$T, GR32:$F, (FCMP_LT GR32:$L, GR32:$R), 1)>;

GR32 is single register class used for i32/f32
and what I want is if the comparison is between f32 values then generate FCMP , $T and $F can be i32/f32 but if I use above pattern table gen fails with “Could not infer all types in pattern”

How to write such pattern matching rule ?

Sincerely,
VIvek

#2

Hello LLVMDevs,

I have following two patterns :
def : Pat<(selectcc (f32 GR32:$L), (f32 GR32:$R),
                    (i32 GR32:$T), (i32 GR32:$F), SETOLT),
          (Select_CC GR32:$T, GR32:$F, (FCMP_LT GR32:$L, GR32:$R), 1)>;
def : Pat<(selectcc (f32 GR32:$L), (f32 GR32:$R),
                    (f32 GR32:$T), (f32 GR32:$F), SETOLT),
          (Select_CC GR32:$T, GR32:$F, (FCMP_LT GR32:$L, GR32:$R), 1)>;

but I want to write it to single pattern like

Pat<(selectcc (f32 GR32:$L), (f32 GR32:$R),
                    GR32:$T, GR32:$F, SETOLT),
          (Select_CC GR32:$T, GR32:$F, (FCMP_LT GR32:$L, GR32:$R), 1)>;

GR32 is single register class used for i32/f32
and what I want is if the comparison is between f32 values then generate FCMP , $T and $F can be i32/f32 but if I use above pattern table gen fails with "Could not infer all types in pattern"

How to write such pattern matching rule ?

You should not use register classes in Pat definitions and should use
types instead, because instruction selection is based on types and
not registers.

I'm not sure there is a way to express these rules with just a single
pattern.

-Tom

#3

You can't. Type inference for instruction selection requires that the final types in a pattern are exact (i.e. that it infers a single type for each node in the pattern), regardless of the output pattern. Since GR32 allows multiple types, you need to specify the two input patterns separately.

-Krzysztof