swift234

Enhance IRGen to know a simple heuristic in emitValueBitCast to avoid
going to the stack when two explosions will end up with the same elements.
This helps with optional to optional conversions.  We now compile:

public func opt_to_opt_trivial(x: Int?) -> Int! { return x }
public func opt_to_opt_reference(x : C!) -> C? { return x }

into:

define { i64, i1 } @_TF1x18opt_to_opt_trivialFGSqSi_GSQSi_(i64, i1) {
entry:
  %2 = insertvalue { i64, i1 } undef, i64 %0, 0
  %3 = insertvalue { i64, i1 } %2, i1 %1, 1
  ret { i64, i1 } %3
}

define i64 @_TF1x20opt_to_opt_referenceFGSQCS_1C_GSqS0__(i64) {
entry:
  ret i64 %0
}

instead of:

define { i64, i1 } @_TF1x18opt_to_opt_trivialFGSqSi_GSQSi_(i64, i1) {
entry:
  %bitcast = alloca %Sq, align 8
  %2 = bitcast %Sq* %bitcast to i64*
  store i64 %0, i64* %2, align 8
  %3 = getelementptr inbounds %Sq, %Sq* %bitcast, i32 0, i32 1
  %4 = bitcast [1 x i8]* %3 to i1*
  store i1 %1, i1* %4, align 8
  %5 = bitcast %Sq* %bitcast to %SQ*
  %6 = bitcast %SQ* %5 to i64*
  %7 = load i64, i64* %6, align 8
  %8 = getelementptr inbounds %SQ, %SQ* %5, i32 0, i32 1
  %9 = bitcast [1 x i8]* %8 to i1*
  %10 = load i1, i1* %9, align 8
  %11 = insertvalue { i64, i1 } undef, i64 %7, 0
  %12 = insertvalue { i64, i1 } %11, i1 %10, 1
  ret { i64, i1 } %12
}

define i64 @_TF1x20opt_to_opt_referenceFGSQCS_1C_GSqS0__(i64) {
entry:
  %bitcast = alloca %SQ.17, align 8
  %1 = bitcast %SQ.17* %bitcast to i64*
  store i64 %0, i64* %1, align 8
  %2 = bitcast %SQ.17* %bitcast to %Sq.16*
  %3 = bitcast %Sq.16* %2 to i64*
  %4 = load i64, i64* %3, align 8
  ret i64 %4
}




Swift SVN r28107