svn commit: r337979 - projects/clang700-import/contrib/llvm/tools/clang/lib/Basic/Targets

[Dimitry Andric]

Author: dim
Date: Fri Aug 17 16:25:59 2018
New Revision: 337979
URL: https://svnweb.freebsd.org/changeset/base/337979

Log:
  For now, revert upstream clang r323281 (by Wei Mi):
  
    Adjust MaxAtomicInlineWidth for i386/i486 targets.
  
    This is to fix the bug reported in
    https://bugs.llvm.org/show_bug.cgi?id=34347#c6.  Currently, all
    MaxAtomicInlineWidth of x86-32 targets are set to 64.  However, i386
    doesn't support any cmpxchg related instructions. i486 only supports
    cmpxchg.  So in this patch MaxAtomicInlineWidth is reset as follows:
    For i386, the MaxAtomicInlineWidth should be 0 because no cmpxchg is
    supported.  For i486, the MaxAtomicInlineWidth should be 32 because
    it supports cmpxchg.  For others 32 bits x86 cpu, the
    MaxAtomicInlineWidth should be 64 because of cmpxchg8b.
  
    Differential Revision: https://reviews.llvm.org/D42154
  
  This should fix buildworld on i386, because of our system libraries
  missing __atomic_load_8, and possibly other 64 bit atomic functions, for
  that architecture.
  
  We should really fix that at some point, but since we have been actually
  using cmpxchg8b for years now, it does not seem to matter much...

Modified:
  projects/clang700-import/contrib/llvm/tools/clang/lib/Basic/Targets/X86.h

Modified: projects/clang700-import/contrib/llvm/tools/clang/lib/Basic/Targets/X86.h
==============================================================================
--- projects/clang700-import/contrib/llvm/tools/clang/lib/Basic/Targets/X86.h	Fri Aug 17 16:19:47 2018	(r337978)
+++ projects/clang700-import/contrib/llvm/tools/clang/lib/Basic/Targets/X86.h	Fri Aug 17 16:25:59 2018	(r337979)
@@ -350,11 +350,9 @@ class LLVM_LIBRARY_VISIBILITY X86_32TargetInfo : publi
          (1 << TargetInfo::LongDouble));
 
     // x86-32 has atomics up to 8 bytes
-    CPUKind Kind = getCPUKind(Opts.CPU);
-    if (Kind >= CK_i586 || Kind == CK_Generic)
-      MaxAtomicPromoteWidth = MaxAtomicInlineWidth = 64;
-    else if (Kind >= CK_i486)
-      MaxAtomicPromoteWidth = MaxAtomicInlineWidth = 32;
+    // FIXME: Check that we actually have cmpxchg8b before setting
+    // MaxAtomicInlineWidth. (cmpxchg8b is an i586 instruction.)
+    MaxAtomicPromoteWidth = MaxAtomicInlineWidth = 64;
   }
 
   BuiltinVaListKind getBuiltinVaListKind() const override {