[LLVMbugs] [Bug 14646] New: Spilled XMM is assumed wrongly to be aligned

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=14646

             Bug #: 14646
           Summary: Spilled XMM is assumed wrongly to be aligned
           Product: libraries
           Version: trunk
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Backend: X86
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: geek4civic at gmail.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified


With XMM, loading m in INSTrm should be 16-byte aligned.

        xorps   (%esp), %xmm0           # 16-byte Folded Reload

But This function does not have realignment in prologue. (%esp) might not be
16-aligned.

It causes miscompilation with i686-cygwin vectorizer.

* Reproducible for i686-freebsd (also possible for netbsd, cygming and win32)
* It's leaf function. This issue could be suppressed if frame pointer were
generated.

/* testcase.c */
typedef long long W __attribute__((__vector_size__(16)));
W foo(W a0) {
  W r0;
  asm
volatile("nop":"=x"(r0)::"%xmm1","%xmm2","%xmm3","xmm4","%xmm5","%xmm6","%xmm7");
  return a0 ^ r0;
}

# llc -mtriple=i686-freebsd -mattr=-avx
foo:                                    # @foo
# BB#0:                                 # %entry
        subl    $28, %esp
        movups  %xmm0, (%esp)           # 16-byte Folded Spill
        #APP
        nop
        #NO_APP
        xorps   (%esp), %xmm0           # 16-byte Folded Reload
        addl    $28, %esp
        ret

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