[llvm] [GVN] Invalidate ICF cache when clearing the instructions (PR #68145)

[Nikita Popov via llvm-commits]

nikic wrote:

Somewhat reduced test case for `-passes=gvn`:
```llvm
declare void @_PyMem_RawFree() nounwind willreturn

define i64 @test(ptr %p) {
entry:
  %a = alloca [2 x ptr], align 8
  %a2 = getelementptr ptr, ptr %a, i64 1
  call void null(ptr %a)
  br i1 false, label %if, label %exit

if:
  %p0 = load ptr, ptr %a, align 8
  %p1 = load ptr, ptr %a2, align 8
  br label %exit

exit:
  store ptr @_PyMem_RawFree, ptr %p
  %p2 = load ptr, ptr %a, align 8
  %pgocount.i = load i64, ptr %p2, align 8
  %fn = load ptr, ptr %p
  tail call void %fn()
  %res = load i64, ptr %a2, align 8
  ret i64 %res
}
```

https://github.com/llvm/llvm-project/pull/68145