LGTM. But I'd like others to make a decision. Thanks!

Fix the error in calculating funclet stack pointer.

Thanks for the patient review and valuable suggestions.

Address review comments.

In D63396#1640095, @rnk wrote:

My suggestion for drastically simplifying this is to modify X86RegisterInfo::eliminateFrameIndex to check if it's lowering an XMM CSR slot. In that case, it would call a new method, X86FrameLowering::getSaveXMMFrameIndexRef, which would contain the logic to check if the current block is a funclet prologue or epilogue. If the parent BB of the current instruction is in a funclet, then XMM slots would be resolved relative to RSP using the funclet frame size. If not, it would delegate to the standard getFrameIndexReference logic, yielding the correct register and offset for XMM slots in non-funclet prologues and epilogues. The prologue code that currently inserts savexmm markers would need to call this new helper as well instead of the standard getFrameIndexReference method. Does that plan seem reasonable?

Update test case to verify XMM registers correctly when MaxCallFrameSize is not 16 bytes aligned.

Add downward alignment for XMM storing in epilogue. This fix the crush when MaxCallFrameSize is not 16 bytes aligned.

Ping.

Thanks for the review.

Refine code as David's proposal

We don't need to consider the upper registers [X,Y,Z]MM16~[X,Y,Z]MM31. So remove the VLX and AVX512 check.

Thanks for the review

Refine code as Craig's proposal

Refine code as Reid's proposal.
Separate the XMM slot caculating so that we can get a consecutive layout in stack.
Also fix an alignment bug due to it affecting this patch.

Reverted by https://reviews.llvm.org/rL362186

In rL361912#653735, @anil9 wrote:

Hello,

It seems your changeset broke this buildbot . There are other prior failures but it seems your changeset introduced some new failures, listed below.
http://lab.llvm.org:8011/builders/clang-ppc64be-linux-lnt?numbuilds=100
http://lab.llvm.org:8011/builders/clang-ppc64be-linux-lnt/builds/27772

Failures are

FAIL: Clang::appletvos-version-min.c
FAIL: Clang::incompatible_sysroot.c
FAIL: Clang::declare_simd_aarch64_warning_advsimd.c
FAIL: Clang::declare_simd_aarch64_warning_sve.c
FAIL: LLVM::arm64-fallback.ll
FAIL: LLVM::irtranslator-volatile-load-pr36018.ll
FAIL: LLVM::irtranslator-block-order.ll
FAIL: LLVM::irtranslator-duplicate-types-param.ll
FAIL: LLVM::regbankselect-unmerge-vec.mir
FAIL: LLVM::regbankselect-default.mir
FAIL: LLVM::arm64-regbankselect.mir

Hi Craig and Yuanke, Could any of you help to submit it? Thank a lot.

LGTM, thanks Erich.

@nikic Thank you very much for your auditing and suggestions.
The test here was just trimmed from the bug repro and used to verify the fix to the assertion. However it exposed that it may be better if it just optimized inside the BB in some cases. We will reserach it later.