@​llvm.assume is ignored in case of pointer values

[llvmbot]

Bugzilla Link	23894
Version	trunk
OS	Linux
Attachments	testcase
Reporter	LLVM Bugzilla Contributor
CC	@hfinkel

Extended Description

@​llvm.assume does not trigger constant propgation in case of pointer values.

eg No constant propagation is done to the return statement for the following code:

struct X { unsigned long long* a; };
unsigned long long* fail(X* x)
{
  __builtin_assume(x->a == (unsigned long long*)12345678);
  return x->a;
}

While for the following code this works as expected:

struct Y { unsigned long long a; };
unsigned long long ok(Y* y)
{
  __builtin_assume(y->a == 12345678);
  return y->a;
}

The attached testcase can be used to reproduce the issue.

[nikic]

This does happen nowadays, performed by SCCP: https://clang.godbolt.org/z/vbsodvPTx

However this transform is actually incorrect due to provenance. I've filed a separate issue for that at #159565.