I’m writing a front end for an existing interpreted language with slightly odd semantics for primitive values.
Similar to the values in a database table, any value could be null, even for non-pointer types.
For example a boolean variable could be true, false, or null.
To model this behaviour, I’m passing an {i1, [type]} around for every numeric type. And using insertvalue / extractvalue all over the place.
So when compiling this simple CS example;
function long fib (long al_x)
long ll_i=0, ll_ret=0, ll_last=0, ll_last2=1
if isnull(al_x) then
return al_x
end if
ll_i=1
do while ll_i<=al_x
ll_ret=ll_last+ll_last2
ll_last2=ll_last
ll_last=ll_ret
ll_i++
loop
return ll_ret
end function
With the following function passes;
FunctionPasses->add(new DataLayout(*JITEngine->getDataLayout()));
FunctionPasses->add(createBasicAliasAnalysisPass());
FunctionPasses->add(createPromoteMemoryToRegisterPass());
FunctionPasses->add(createInstructionCombiningPass());
FunctionPasses->add(createReassociatePass());
FunctionPasses->add(createGVNPass());
FunctionPasses->add(createCFGSimplificationPass());
Which does a pretty good job of cleaning up most of the messy & verbose code generated by my front end.
I end up with the following bitcode;
define x86_stdcallcc { i1, i32 } @fib({ i1, i32 } %arg_al_x) {
entry:
%“3_4” = extractvalue { i1, i32 } %arg_al_x, 0
br i1 %“3_4”, label %Line15_Offset120, label %Line8_Offset38
Line8_Offset38: ; preds = %Line9_Offset52, %entry
%ll_last2.0 = phi { i1, i32 } [ %ll_last.0, %Line9_Offset52 ], [ { i1 false, i32 1 }, %entry ]
%ll_last.0 = phi { i1, i32 } [ %“9_64_composed”, %Line9_Offset52 ], [ zeroinitializer, %entry ]
%ll_i.0 = phi { i1, i32 } [ %“12_98”, %Line9_Offset52 ], [ { i1 false, i32 1 }, %entry ]
%“8_38_isnull” = extractvalue { i1, i32 } %ll_i.0, 0
%“8_38_value” = extractvalue { i1, i32 } %ll_i.0, 1
%“8_42_value” = extractvalue { i1, i32 } %arg_al_x, 1
%“8_46_value” = icmp sle i32 %“8_38_value”, %“8_42_value”
%“8_48_not_null” = xor i1 %“8_38_isnull”, true
%“8_48_and_not_null” = and i1 %“8_46_value”, %“8_48_not_null”
br i1 %“8_48_and_not_null”, label %Line9_Offset52, label %Line15_Offset120
Line9_Offset52: ; preds = %Line8_Offset38
%“9_60_isnull” = extractvalue { i1, i32 } %ll_last2.0, 0
%“9_56_isnull” = extractvalue { i1, i32 } %ll_last.0, 0
%“9_64_isnull” = or i1 %“9_56_isnull”, %“9_60_isnull”
%“9_56_value” = extractvalue { i1, i32 } %ll_last.0, 1
%“9_60_value” = extractvalue { i1, i32 } %ll_last2.0, 1
%“9_64” = add i32 %“9_56_value”, %“9_60_value”
%0 = insertvalue { i1, i32 } zeroinitializer, i1 %“9_64_isnull”, 0
%“9_64_composed” = insertvalue { i1, i32 } %0, i32 %“9_64”, 1
%“12_98_value” = add i32 %“8_38_value”, 1
%1 = insertvalue { i1, i32 } zeroinitializer, i1 %“8_38_isnull”, 0
%“12_98” = insertvalue { i1, i32 } %1, i32 %“12_98_value”, 1
br label %Line8_Offset38
Line15_Offset120: ; preds = %Line8_Offset38, %entry
%_return_value.0 = phi { i1, i32 } [ %arg_al_x, %entry ], [ %ll_last.0, %Line8_Offset38 ]
ret { i1, i32 } %_return_value.0
}
None of the local variables in this example can ever be null. Each of these extractvalue expressions will always evaluate to i1 0;
%“8_38_isnull” = extractvalue { i1, i32 } %ll_i.0, 0
%“9_60_isnull” = extractvalue { i1, i32 } %ll_last2.0, 0
%“9_56_isnull” = extractvalue { i1, i32 } %ll_last.0, 0
Is there an existing function pass I could add that would clean this up? Or is this example just slightly too complex?