Transforms/InstCombine/InstructionCombining.cpp

979         APInt SmallScale = Scale.trunc(SmallSize);
980         // Suppose Op = sext X, and we descale X as Y * SmallScale.  We want to
982         //   sext (Y * SmallScale) = (sext Y) * Scale
983         // some conditions need to hold however: SmallScale must sign-extend to
984         // Scale and the multiplication Y * SmallScale should not overflow.
985         if (SmallScale.sext(Scale.getBitWidth()) != Scale)
986           // SmallScale does not sign-extend to Scale.
988         assert(SmallScale.exactLogBase2() == logScale);
989         // Require that Y * SmallScale must not overflow.
994         Scale = SmallScale;