Example of use-tracking API with modification of value.

use-example.go

// nopTrunc propagates From values of truncation instructions that have no
// effect on type (where From and To type are the same).
//
// Example:
//
// before:
//    %10 = xor i32 %src2, %src1
//    %11 = trunc i32 %10 to i32
//    %12 = xor i32 %sum, %11
//
// after:
//    %10 = xor i32 %src2, %src1
//    %11 = trunc i32 %10 to i32
//    ; note use of %10 instead of %11, as trunc was applied from i32 to i32
//    %12 = xor i32 %sum, %10
func nopTrunc(f *ir.Func) {
	uses := irutil.FuncUses(nil, f)
	for _, use := range uses {
		truncInst, ok := (*use.Val).(*ir.InstTrunc)
		if !ok {
			continue
		}
		// Check if types of From and To are equal.
		if !types.Equal(truncInst.From.Type(), truncInst.To) {
			continue
		}
		// Types of From and To are equal, propagate From and skip trunc
		// instruction.
		*use.Val = truncInst.From
	}
}