Andrew Trick c47fe03241 Optimize Builtin.assumeAlignment -> pointer_to_address ...

Case #1. Literal zero = natural alignment
   %1 = integer_literal $Builtin.Int64, 0
   %2 = builtin "uncheckedAssertAlignment"
	(%0 : $Builtin.RawPointer, %1 : $Builtin.Int64) : $Builtin.RawPointer
   %3 = pointer_to_address %2 : $Builtin.RawPointer to [align=1] $*Int

   Erases the `pointer_to_address` `[align=]` attribute:

Case #2. Literal nonzero = forced alignment.

   %1 = integer_literal $Builtin.Int64, 16
   %2 = builtin "uncheckedAssertAlignment"
	(%0 : $Builtin.RawPointer, %1 : $Builtin.Int64) : $Builtin.RawPointer
   %3 = pointer_to_address %2 : $Builtin.RawPointer to [align=1] $*Int

   Promotes the `pointer_to_address` `[align=]` attribute to a higher value.

Case #3. Folded dynamic alignment

   %1 = builtin "alignof"<T>(%0 : $@thin T.Type) : $Builtin.Word
   %2 = builtin "uncheckedAssertAlignment"
	(%0 : $Builtin.RawPointer, %1 : $Builtin.Int64) : $Builtin.RawPointer
   %3 = pointer_to_address %2 : $Builtin.RawPointer to [align=1] $*T

   Erases the `pointer_to_address` `[align=]` attribute.

2021-11-30 12:23:46 -08:00

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