[all-commits] [llvm/llvm-project] d8b6ae: [PPCISelLowering] avoid emitting libcalls to __mul...

[Nick Desaulniers via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: d8b6ae072d7734e2abadd54ecddfd6cb77b7e4c0
      https://github.com/llvm/llvm-project/commit/d8b6ae072d7734e2abadd54ecddfd6cb77b7e4c0
  Author: Nick Desaulniers <ndesaulniers at google.com>
  Date:   2021-08-31 (Tue, 31 Aug 2021)

  Changed paths:
    M llvm/lib/Target/PowerPC/PPCISelLowering.cpp
    A llvm/test/CodeGen/PowerPC/overflow-intrinsic-optimizations.ll

  Log Message:
  -----------
  [PPCISelLowering] avoid emitting libcalls to __mulodi4()

Similar to D108842, D108844, and D108926.

__has_builtin(builtin_mul_overflow) returns true for 32b PPC targets,
but Clang is deferring to compiler RT when encountering long long types.
This breaks ppc44x_defconfig + CONFIG_BLK_DEV_NBD=y builds of the Linux
kernel that are using builtin_mul_overflow with these types for these
targets.

If the semantics of __has_builtin mean "the compiler resolves these,
always" then we shouldn't conditionally emit a libcall.

This will still need to be worked around in the Linux kernel in order to
continue to support these builds of the Linux kernel for this
target with older releases of clang.

Link: https://bugs.llvm.org/show_bug.cgi?id=28629
Link: https://github.com/ClangBuiltLinux/linux/issues/1438

Reviewed By: nemanjai

Differential Revision: https://reviews.llvm.org/D108936