http://llvm.org/bugs/show_bug.cgi?id=16674
Bug ID: 16674
Summary: AVX code is generated even if OS doesn't support AVX
Product: new-bugs
Version: unspecified
Hardware: PC
OS: Windows XP
Status: NEW
Severity: normal
Priority: P
Component: new bugs
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Classification: Unclassified
The MSVC case in OSHasAVXSupport() in lib/Support/Host.cpp and
lib/Target/X86/X86Subtarget.cpp uses _xgetbv(_XCR_XFEATURE_ENABLED_MASK) to
detect if the OS supports saving and restoring of AVX registers on context
switches.
But this test also succeeds in vSphere and KVM guests if the host CPU supports
AVX and the extension is enabled for the guest CPU. If the guest OS doesn't
support this (everything < Windows 7 SP1), a generated AVX insn then triggers
an invalid opcode exception.
Tested this with Mesa's llvmpipe OpenGL driver on:
* LLVM 3.2 + Mesa 9.1.2
* LLVM 3.3 + Mesa 9.1.5
Both trigger said exception on a XP SP3 guest.
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