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Describe what's going on with mingw alloca and why do we need separate instruction.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@97888 91177308-0d34-0410-b5e6-96231b3b80d8
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Anton Korobeynikov 2010-03-06 20:07:32 +00:00
parent ce7bf1c55f
commit e765f2b5e3
1 changed files with 9 additions and 1 deletions
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10
lib/Target/X86/X86InstrInfo.td
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@ -533,8 +533,16 @@ def VASTART_SAVE_XMM_REGS : I<0, Pseudo,
imm:$regsavefi,
imm:$offset)]>;
// Dynamic stack allocation yields _alloca call for Cygwin/Mingw targets. Calls
// to _alloca is needed to probe the stack when allocating more than 4k bytes in
// one go. Touching the stack at 4K increments is necessary to ensure that the
// guard pages used by the OS virtual memory manager are allocated in correct
// sequence.
// The main point of having separate instruction are extra unmodelled effects
// (compared to ordinary calls) like stack pointer change.
def MINGW_ALLOCA : I<0, Pseudo, (outs), (ins),
"call __alloca",
"# dynamic stack allocation",
[(X86MingwAlloca)]>;
}