forked from OSchip/llvm-project
MC/Expr: Implemnt more aggressive folding during symbol evaluation using
IsSymbolRefDifferenceFullyResolved(). For example, we will now fold away something like: -- _a: ... L0: ... L1: ... .long (L1 - L0) / 2 -- llvm-svn: 122043
This commit is contained in:
Daniel Dunbar
parent
2ee6c9b8c9
commit
137d422e50
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@ -271,6 +271,25 @@ bool MCExpr::EvaluateAsAbsolute(int64_t &Res, const MCAsmLayout *Layout,
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return true;
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}
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/// \brief Helper method for \see EvaluateSymbolAdd().
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static void AttemptToFoldSymbolOffsetDifference(const MCAsmLayout *Layout,
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const MCSymbolRefExpr *&A,
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const MCSymbolRefExpr *&B,
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int64_t &Addend) {
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const MCAssembler &Asm = Layout->getAssembler();
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if (A && B &&
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Asm.getWriter().IsSymbolRefDifferenceFullyResolved(Asm, A, B)) {
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// Eagerly evaluate.
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Addend += (Layout->getSymbolOffset(&Asm.getSymbolData(A->getSymbol())) -
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Layout->getSymbolOffset(&Asm.getSymbolData(B->getSymbol())));
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// Clear the symbol expr pointers to indicate we have folded these
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// operands.
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A = B = 0;
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}
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}
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/// \brief Evaluate the result of an add between (conceptually) two MCValues.
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///
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/// This routine conceptually attempts to construct an MCValue:
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@ -300,20 +319,37 @@ static bool EvaluateSymbolicAdd(const MCAsmLayout *Layout,
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// Fold the result constant immediately.
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int64_t Result_Cst = LHS_Cst + RHS_Cst;
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// If we have a layout, we can fold resolved differences.
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if (Layout) {
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// First, fold out any differences which are fully resolved. By
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// reassociating terms in
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// Result = (LHS_A - LHS_B + LHS_Cst) + (RHS_A - RHS_B + RHS_Cst).
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// we have the four possible differences:
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// (LHS_A - LHS_B),
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// (LHS_A - RHS_B),
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// (RHS_A - LHS_B),
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// (RHS_A - RHS_B).
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// Since we are attempting to be as aggresive as possible about folding, we
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// attempt to evaluate each possible alternative.
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AttemptToFoldSymbolOffsetDifference(Layout, LHS_A, LHS_B, Result_Cst);
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AttemptToFoldSymbolOffsetDifference(Layout, LHS_A, RHS_B, Result_Cst);
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AttemptToFoldSymbolOffsetDifference(Layout, RHS_A, LHS_B, Result_Cst);
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AttemptToFoldSymbolOffsetDifference(Layout, RHS_A, RHS_B, Result_Cst);
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}
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// We can't represent the addition or subtraction of two symbols.
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if ((LHS_A && RHS_A) || (LHS_B && RHS_B))
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return false;
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// At this point, we have at most one additive symbol and one subtractive
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// symbol -- find them.
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const MCSymbolRefExpr *A = LHS_A ? LHS_A : RHS_A;
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const MCSymbolRefExpr *B = LHS_B ? LHS_B : RHS_B;
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if (B) {
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// If we have a negated symbol, then we must have also have a non-negated
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// symbol in order to encode the expression. We can do this check later to
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// permit expressions which eventually fold to a representable form -- such
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// as (a + (0 - b)) -- if necessary.
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if (!A)
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return false;
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}
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// If we have a negated symbol, then we must have also have a non-negated
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// symbol in order to encode the expression.
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if (B && !A)
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return false;
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// Absolutize symbol differences between defined symbols when we have a
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// layout object and the target requests it.
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@ -0,0 +1,129 @@
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// RUN: llvm-mc -triple x86_64-apple-darwin10 %s -filetype=obj -o %t.o
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// RUN: macho-dump --dump-section-data < %t.o > %t.dump
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// RUN: FileCheck < %t.dump %s
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_a:
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L0:
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.long 1
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L1:
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.long 2
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.long _c - _d + 4
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.long (_c - L0) - (_d - L1) // == (_c - _d) + (L1 - L0)
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// == (_c - _d + 4)
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_c:
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.long 0
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_d:
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.long 0
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// CHECK: ('cputype', 16777223)
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// CHECK: ('cpusubtype', 3)
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// CHECK: ('filetype', 1)
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// CHECK: ('num_load_commands', 3)
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// CHECK: ('load_commands_size', 256)
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// CHECK: ('flag', 0)
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// CHECK: ('reserved', 0)
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// CHECK: ('load_commands', [
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// CHECK: # Load Command 0
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// CHECK: (('command', 25)
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// CHECK: ('size', 152)
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// CHECK: ('segment_name', '\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00')
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// CHECK: ('vm_addr', 0)
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// CHECK: ('vm_size', 24)
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// CHECK: ('file_offset', 288)
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// CHECK: ('file_size', 24)
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// CHECK: ('maxprot', 7)
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// CHECK: ('initprot', 7)
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// CHECK: ('num_sections', 1)
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// CHECK: ('flags', 0)
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// CHECK: ('sections', [
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// CHECK: # Section 0
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// CHECK: (('section_name', '__text\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00')
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// CHECK: ('segment_name', '__TEXT\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00')
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// CHECK: ('address', 0)
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// CHECK: ('size', 24)
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// CHECK: ('offset', 288)
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// CHECK: ('alignment', 0)
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// CHECK: ('reloc_offset', 312)
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// CHECK: ('num_reloc', 4)
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// CHECK: ('flags', 0x80000000)
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// CHECK: ('reserved1', 0)
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// CHECK: ('reserved2', 0)
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// CHECK: ('reserved3', 0)
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// CHECK: ),
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// CHECK: ('_relocations', [
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// CHECK: # Relocation 0
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// CHECK: (('word-0', 0xc),
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// CHECK: ('word-1', 0x5c000002)),
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// CHECK: # Relocation 1
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// CHECK: (('word-0', 0xc),
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// CHECK: ('word-1', 0xc000001)),
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// CHECK: # Relocation 2
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// CHECK: (('word-0', 0x8),
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// CHECK: ('word-1', 0x5c000002)),
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// CHECK: # Relocation 3
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// CHECK: (('word-0', 0x8),
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// CHECK: ('word-1', 0xc000001)),
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// CHECK: ])
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// CHECK: ('_section_data', '01000000 02000000 04000000 04000000 00000000 00000000')
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// CHECK: ])
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// CHECK: ),
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// CHECK: # Load Command 1
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// CHECK: (('command', 2)
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// CHECK: ('size', 24)
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// CHECK: ('symoff', 344)
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// CHECK: ('nsyms', 3)
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// CHECK: ('stroff', 392)
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// CHECK: ('strsize', 12)
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// CHECK: ('_string_data', '\x00_a\x00_c\x00_d\x00\x00\x00')
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// CHECK: ('_symbols', [
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// CHECK: # Symbol 0
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// CHECK: (('n_strx', 1)
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// CHECK: ('n_type', 0xe)
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// CHECK: ('n_sect', 1)
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// CHECK: ('n_desc', 0)
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// CHECK: ('n_value', 0)
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// CHECK: ('_string', '_a')
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// CHECK: ),
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// CHECK: # Symbol 1
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// CHECK: (('n_strx', 4)
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// CHECK: ('n_type', 0xe)
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// CHECK: ('n_sect', 1)
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// CHECK: ('n_desc', 0)
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// CHECK: ('n_value', 16)
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// CHECK: ('_string', '_c')
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// CHECK: ),
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// CHECK: # Symbol 2
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// CHECK: (('n_strx', 7)
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// CHECK: ('n_type', 0xe)
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// CHECK: ('n_sect', 1)
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// CHECK: ('n_desc', 0)
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// CHECK: ('n_value', 20)
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// CHECK: ('_string', '_d')
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// CHECK: ),
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// CHECK: ])
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// CHECK: ),
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// CHECK: # Load Command 2
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// CHECK: (('command', 11)
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// CHECK: ('size', 80)
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// CHECK: ('ilocalsym', 0)
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// CHECK: ('nlocalsym', 3)
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// CHECK: ('iextdefsym', 3)
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// CHECK: ('nextdefsym', 0)
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// CHECK: ('iundefsym', 3)
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// CHECK: ('nundefsym', 0)
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// CHECK: ('tocoff', 0)
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// CHECK: ('ntoc', 0)
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// CHECK: ('modtaboff', 0)
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// CHECK: ('nmodtab', 0)
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// CHECK: ('extrefsymoff', 0)
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// CHECK: ('nextrefsyms', 0)
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// CHECK: ('indirectsymoff', 0)
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// CHECK: ('nindirectsyms', 0)
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// CHECK: ('extreloff', 0)
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// CHECK: ('nextrel', 0)
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// CHECK: ('locreloff', 0)
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// CHECK: ('nlocrel', 0)
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// CHECK: ('_indirect_symbols', [
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// CHECK: ])
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// CHECK: ),
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// CHECK: ])
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