Recommit r332501, with an additional upstream fix for "Cannot lower

EFLAGS copy that lives out of a basic block!" errors on i386.

Pull in r325446 from upstream clang trunk (by me):

  [X86] Add 'sahf' CPU feature to frontend

  Summary:
  Make clang accept `-msahf` (and `-mno-sahf`) flags to activate the
  `+sahf` feature for the backend, for bug 36028 (Incorrect use of
  pushf/popf enables/disables interrupts on amd64 kernels).  This was
  originally submitted in bug 36037 by Jonathan Looney
  <jonlooney@gmail.com>.

  As described there, GCC also uses `-msahf` for this feature, and the
  backend already recognizes the `+sahf` feature. All that is needed is
  to teach clang to pass this on to the backend.

  The mapping of feature support onto CPUs may not be complete; rather,
  it was chosen to match LLVM's idea of which CPUs support this feature
  (see lib/Target/X86/X86.td).

  I also updated the affected test case (CodeGen/attr-target-x86.c) to
  match the emitted output.

  Reviewers: craig.topper, coby, efriedma, rsmith

  Reviewed By: craig.topper

  Subscribers: emaste, cfe-commits

  Differential Revision: https://reviews.llvm.org/D43394

Pull in r328944 from upstream llvm trunk (by Chandler Carruth):

  [x86] Expose more of the condition conversion routines in the public
  API for X86's instruction information. I've now got a second patch
  under review that needs these same APIs. This bit is nicely
  orthogonal and obvious, so landing it. NFC.

Pull in r329414 from upstream llvm trunk (by Craig Topper):

  [X86] Merge itineraries for CLC, CMC, and STC.

  These are very simple flag setting instructions that appear to only
  be a single uop. They're unlikely to need this separation.

Pull in r329657 from upstream llvm trunk (by Chandler Carruth):

  [x86] Introduce a pass to begin more systematically fixing PR36028
  and similar issues.

  The key idea is to lower COPY nodes populating EFLAGS by scanning the
  uses of EFLAGS and introducing dedicated code to preserve the
  necessary state in a GPR. In the vast majority of cases, these uses
  are cmovCC and jCC instructions. For such cases, we can very easily
  save and restore the necessary information by simply inserting a
  setCC into a GPR where the original flags are live, and then testing
  that GPR directly to feed the cmov or conditional branch.

  However, things are a bit more tricky if arithmetic is using the
  flags.  This patch handles the vast majority of cases that seem to
  come up in practice: adc, adcx, adox, rcl, and rcr; all without
  taking advantage of partially preserved EFLAGS as LLVM doesn't
  currently model that at all.

  There are a large number of operations that techinaclly observe
  EFLAGS currently but shouldn't in this case -- they typically are
  using DF.  Currently, they will not be handled by this approach.
  However, I have never seen this issue come up in practice. It is
  already pretty rare to have these patterns come up in practical code
  with LLVM. I had to resort to writing MIR tests to cover most of the
  logic in this pass already.  I suspect even with its current amount
  of coverage of arithmetic users of EFLAGS it will be a significant
  improvement over the current use of pushf/popf. It will also produce
  substantially faster code in most of the common patterns.

  This patch also removes all of the old lowering for EFLAGS copies,
  and the hack that forced us to use a frame pointer when EFLAGS copies
  were found anywhere in a function so that the dynamic stack
  adjustment wasn't a problem. None of this is needed as we now lower
  all of these copies directly in MI and without require stack
  adjustments.

  Lots of thanks to Reid who came up with several aspects of this
  approach, and Craig who helped me work out a couple of things
  tripping me up while working on this.

  Differential Revision: https://reviews.llvm.org/D45146

Pull in r329673 from upstream llvm trunk (by Chandler Carruth):

  [x86] Model the direction flag (DF) separately from the rest of
  EFLAGS.

  This cleans up a number of operations that only claimed te use EFLAGS
  due to using DF. But no instructions which we think of us setting
  EFLAGS actually modify DF (other than things like popf) and so this
  needlessly creates uses of EFLAGS that aren't really there.

  In fact, DF is so restrictive it is pretty easy to model. Only STD,
  CLD, and the whole-flags writes (WRFLAGS and POPF) need to model
  this.

  I've also somewhat cleaned up some of the flag management instruction
  definitions to be in the correct .td file.

  Adding this extra register also uncovered a failure to use the
  correct datatype to hold X86 registers, and I've corrected that as
  necessary here.

  Differential Revision: https://reviews.llvm.org/D45154

Pull in r330264 from upstream llvm trunk (by Chandler Carruth):

  [x86] Fix PR37100 by teaching the EFLAGS copy lowering to rewrite
  uses across basic blocks in the limited cases where it is very
  straight forward to do so.

  This will also be useful for other places where we do some limited
  EFLAGS propagation across CFG edges and need to handle copy rewrites
  afterward. I think this is rapidly approaching the maximum we can and
  should be doing here. Everything else begins to require either heroic
  analysis to prove how to do PHI insertion manually, or somehow
  managing arbitrary PHI-ing of EFLAGS with general PHI insertion.
  Neither of these seem at all promising so if those cases come up,
  we'll almost certainly need to rewrite the parts of LLVM that produce
  those patterns.

  We do now require dominator trees in order to reliably diagnose
  patterns that would require PHI nodes. This is a bit unfortunate but
  it seems better than the completely mysterious crash we would get
  otherwise.

  Differential Revision: https://reviews.llvm.org/D45673

Together, these should ensure clang does not use pushf/popf sequences to
save and restore flags, avoiding problems with unrelated flags (such as
the interrupt flag) being restored unexpectedly.

Requested by:	jtl
PR:		225330
MFC after:	1 week

0 files changed, 0 insertions, 0 deletions