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...i need to replace them all with the same freeze def in order to be >> able to consider them the same value, (...) >> >> Right, so just to make it very clear, the following would be wrong: >> %x = freeze %y >> %w = freeze %y >> use_1 %x >> use_2 %w >> use_3 %x >> => >> %x = freeze %y >> %w = freeze %y >> use_1 %w >> use_2 %w >> use_3 %x >> >> If you replace one use of %x, all uses have to be replaced, since >> different freezes of the same operand *may* return different values. >> I guess...

...an atomic/volatile operation seems like a good intuition. > *If* i need to replace them all with the same freeze def in order to be able to consider them the same value, (...) Right, so just to make it very clear, the following would be wrong: %x = freeze %y %w = freeze %y use_1 %x use_2 %w use_3 %x => %x = freeze %y %w = freeze %y use_1 %w use_2 %w use_3 %x If you replace one use of %x, all uses have to be replaced, since different freezes of the same operand *may* return different values. I guess that since we are never (err, most of the times) sure of whether a value may come out of...

...r to > be able to consider them the same value, (...) > >>> > >>> Right, so just to make it very clear, the following would be wrong: > >>> %x = freeze %y > >>> %w = freeze %y > >>> use_1 %x > >>> use_2 %w > >>> use_3 %x > >>> => > >>> %x = freeze %y > >>> %w = freeze %y > >>> use_1 %w > >>> use_2 %w > >>> use_3 %x > >>> > >>> If you replace one use of %x, all uses have to be replaced, since > different freezes...

The fact two IR values are defined the same way doesn't necessarily imply they are actually the same value. e.g. %a = load volatile i32, i32* %p %b = load volatile i32, i32* %p As Sanjoy said, though, it should always be legal to optimize all uses of different "freeze(%x)" values to use the same def - this is equivalent to choosing the same value for all freezes. It's just not