[llvm-bugs] [Bug 47874] New: spilling general registers through xmm registers

via llvm-bugs llvm-bugs at lists.llvm.org
Fri Oct 16 00:11:46 PDT 2020


            Bug ID: 47874
           Summary: spilling general registers through xmm registers
           Product: libraries
           Version: 11.0
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: normal
          Priority: P
         Component: Backend: X86
          Assignee: unassignedbugs at nondot.org
          Reporter: jeffr at radgametools.com
                CC: craig.topper at gmail.com, llvm-bugs at lists.llvm.org,
                    llvm-dev at redking.me.uk, pengfei.wang at intel.com,
                    spatel+llvm at rotateright.com

We just updated to clang 11 (from 9), and I'm seeing a lot of this kind of
codegen, when spilling registers to the stack:

 66 0f 6e c1                    movd    %ecx, %xmm0
 66 0f 7f 85 60 fe ff ff        movdqa  %xmm0, -416(%rbp)
 66 0f 6e c6                    movd    %esi, %xmm0
 66 0f 7f 85 70 fe ff ff        movdqa  %xmm0, -400(%rbp)

What's going on here?  Why aren't we just copying ecr and esi directly to those
splill locations?

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