The test file against the ValueTracking pass

test.ll

; ModuleID = 'test'
source_filename = "test.c"
target datalayout = "e-m:e-i64:64-n32:64"

declare void @llvm.assume(i1)

define i32 @demo(i32 %x, i32 %y) {
entry:
  ; Assume x >= 1  (=> nonzero, clears sign info)
  %cmp = icmp sge i32 %x, 1
  call void @llvm.assume(i1 %cmp)

  ; pow2 = x & -x  -> known power-of-two (lowbit)
  %negx = sub i32 0, %x
  %pow2 = and i32 %x, %negx

  ; high = shl nuw i32 1, 8           ; NUW helps known bits
  %high = shl nuw i32 1, 8

  ; mix = or i32 %pow2, %high
  %mix  = or i32 %pow2, %high

  ; only low 8 bits used later (lets demanded-bits fold)
  %trunc = trunc i32 %mix to i8
  %zext  = zext i8 %trunc to i32

  ; FP: start from positive finite number
  %f = fadd nnan nsz float 1.0, 2.0     ; no NaN, not negative zero
  %g = fmul nnan nsz float %f, 0x3F800000 ; *1.0

  ret i32 %zext
}

define i32 @ptr_demo(i32* nonnull align 16 %p) {
entry:
  ; load from a nonnull, 16-aligned pointer
  %v = load i32, i32* %p, align 16
  ret i32 %v
}