From 137d422e507136110b10c7a7d4ee88065b496eca Mon Sep 17 00:00:00 2001 From: Daniel Dunbar Date: Fri, 17 Dec 2010 05:50:33 +0000 Subject: [PATCH] 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 --- llvm/lib/MC/MCExpr.cpp | 52 +++++-- .../test/MC/MachO/darwin-complex-difference.s | 129 ++++++++++++++++++ 2 files changed, 173 insertions(+), 8 deletions(-) create mode 100644 llvm/test/MC/MachO/darwin-complex-difference.s diff --git a/llvm/lib/MC/MCExpr.cpp b/llvm/lib/MC/MCExpr.cpp index 4465104bfe5e..41feaa837573 100644 --- a/llvm/lib/MC/MCExpr.cpp +++ b/llvm/lib/MC/MCExpr.cpp @@ -271,6 +271,25 @@ bool MCExpr::EvaluateAsAbsolute(int64_t &Res, const MCAsmLayout *Layout, return true; } +/// \brief Helper method for \see EvaluateSymbolAdd(). +static void AttemptToFoldSymbolOffsetDifference(const MCAsmLayout *Layout, + const MCSymbolRefExpr *&A, + const MCSymbolRefExpr *&B, + int64_t &Addend) { + const MCAssembler &Asm = Layout->getAssembler(); + + if (A && B && + Asm.getWriter().IsSymbolRefDifferenceFullyResolved(Asm, A, B)) { + // Eagerly evaluate. + Addend += (Layout->getSymbolOffset(&Asm.getSymbolData(A->getSymbol())) - + Layout->getSymbolOffset(&Asm.getSymbolData(B->getSymbol()))); + + // Clear the symbol expr pointers to indicate we have folded these + // operands. + A = B = 0; + } +} + /// \brief Evaluate the result of an add between (conceptually) two MCValues. /// /// This routine conceptually attempts to construct an MCValue: @@ -300,20 +319,37 @@ static bool EvaluateSymbolicAdd(const MCAsmLayout *Layout, // Fold the result constant immediately. int64_t Result_Cst = LHS_Cst + RHS_Cst; + // If we have a layout, we can fold resolved differences. + if (Layout) { + // First, fold out any differences which are fully resolved. By + // reassociating terms in + // Result = (LHS_A - LHS_B + LHS_Cst) + (RHS_A - RHS_B + RHS_Cst). + // we have the four possible differences: + // (LHS_A - LHS_B), + // (LHS_A - RHS_B), + // (RHS_A - LHS_B), + // (RHS_A - RHS_B). + // Since we are attempting to be as aggresive as possible about folding, we + // attempt to evaluate each possible alternative. + AttemptToFoldSymbolOffsetDifference(Layout, LHS_A, LHS_B, Result_Cst); + AttemptToFoldSymbolOffsetDifference(Layout, LHS_A, RHS_B, Result_Cst); + AttemptToFoldSymbolOffsetDifference(Layout, RHS_A, LHS_B, Result_Cst); + AttemptToFoldSymbolOffsetDifference(Layout, RHS_A, RHS_B, Result_Cst); + } + // We can't represent the addition or subtraction of two symbols. if ((LHS_A && RHS_A) || (LHS_B && RHS_B)) return false; + // At this point, we have at most one additive symbol and one subtractive + // symbol -- find them. const MCSymbolRefExpr *A = LHS_A ? LHS_A : RHS_A; const MCSymbolRefExpr *B = LHS_B ? LHS_B : RHS_B; - if (B) { - // If we have a negated symbol, then we must have also have a non-negated - // symbol in order to encode the expression. We can do this check later to - // permit expressions which eventually fold to a representable form -- such - // as (a + (0 - b)) -- if necessary. - if (!A) - return false; - } + + // If we have a negated symbol, then we must have also have a non-negated + // symbol in order to encode the expression. + if (B && !A) + return false; // Absolutize symbol differences between defined symbols when we have a // layout object and the target requests it. diff --git a/llvm/test/MC/MachO/darwin-complex-difference.s b/llvm/test/MC/MachO/darwin-complex-difference.s new file mode 100644 index 000000000000..e66bd096711f --- /dev/null +++ b/llvm/test/MC/MachO/darwin-complex-difference.s @@ -0,0 +1,129 @@ +// RUN: llvm-mc -triple x86_64-apple-darwin10 %s -filetype=obj -o %t.o +// RUN: macho-dump --dump-section-data < %t.o > %t.dump +// RUN: FileCheck < %t.dump %s + +_a: +L0: + .long 1 +L1: + .long 2 + .long _c - _d + 4 + .long (_c - L0) - (_d - L1) // == (_c - _d) + (L1 - L0) + // == (_c - _d + 4) +_c: + .long 0 +_d: + .long 0 + +// CHECK: ('cputype', 16777223) +// CHECK: ('cpusubtype', 3) +// CHECK: ('filetype', 1) +// CHECK: ('num_load_commands', 3) +// CHECK: ('load_commands_size', 256) +// CHECK: ('flag', 0) +// CHECK: ('reserved', 0) +// CHECK: ('load_commands', [ +// CHECK: # Load Command 0 +// CHECK: (('command', 25) +// CHECK: ('size', 152) +// CHECK: ('segment_name', '\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00') +// CHECK: ('vm_addr', 0) +// CHECK: ('vm_size', 24) +// CHECK: ('file_offset', 288) +// CHECK: ('file_size', 24) +// CHECK: ('maxprot', 7) +// CHECK: ('initprot', 7) +// CHECK: ('num_sections', 1) +// CHECK: ('flags', 0) +// CHECK: ('sections', [ +// CHECK: # Section 0 +// CHECK: (('section_name', '__text\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00') +// CHECK: ('segment_name', '__TEXT\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00') +// CHECK: ('address', 0) +// CHECK: ('size', 24) +// CHECK: ('offset', 288) +// CHECK: ('alignment', 0) +// CHECK: ('reloc_offset', 312) +// CHECK: ('num_reloc', 4) +// CHECK: ('flags', 0x80000000) +// CHECK: ('reserved1', 0) +// CHECK: ('reserved2', 0) +// CHECK: ('reserved3', 0) +// CHECK: ), +// CHECK: ('_relocations', [ +// CHECK: # Relocation 0 +// CHECK: (('word-0', 0xc), +// CHECK: ('word-1', 0x5c000002)), +// CHECK: # Relocation 1 +// CHECK: (('word-0', 0xc), +// CHECK: ('word-1', 0xc000001)), +// CHECK: # Relocation 2 +// CHECK: (('word-0', 0x8), +// CHECK: ('word-1', 0x5c000002)), +// CHECK: # Relocation 3 +// CHECK: (('word-0', 0x8), +// CHECK: ('word-1', 0xc000001)), +// CHECK: ]) +// CHECK: ('_section_data', '01000000 02000000 04000000 04000000 00000000 00000000') +// CHECK: ]) +// CHECK: ), +// CHECK: # Load Command 1 +// CHECK: (('command', 2) +// CHECK: ('size', 24) +// CHECK: ('symoff', 344) +// CHECK: ('nsyms', 3) +// CHECK: ('stroff', 392) +// CHECK: ('strsize', 12) +// CHECK: ('_string_data', '\x00_a\x00_c\x00_d\x00\x00\x00') +// CHECK: ('_symbols', [ +// CHECK: # Symbol 0 +// CHECK: (('n_strx', 1) +// CHECK: ('n_type', 0xe) +// CHECK: ('n_sect', 1) +// CHECK: ('n_desc', 0) +// CHECK: ('n_value', 0) +// CHECK: ('_string', '_a') +// CHECK: ), +// CHECK: # Symbol 1 +// CHECK: (('n_strx', 4) +// CHECK: ('n_type', 0xe) +// CHECK: ('n_sect', 1) +// CHECK: ('n_desc', 0) +// CHECK: ('n_value', 16) +// CHECK: ('_string', '_c') +// CHECK: ), +// CHECK: # Symbol 2 +// CHECK: (('n_strx', 7) +// CHECK: ('n_type', 0xe) +// CHECK: ('n_sect', 1) +// CHECK: ('n_desc', 0) +// CHECK: ('n_value', 20) +// CHECK: ('_string', '_d') +// CHECK: ), +// CHECK: ]) +// CHECK: ), +// CHECK: # Load Command 2 +// CHECK: (('command', 11) +// CHECK: ('size', 80) +// CHECK: ('ilocalsym', 0) +// CHECK: ('nlocalsym', 3) +// CHECK: ('iextdefsym', 3) +// CHECK: ('nextdefsym', 0) +// CHECK: ('iundefsym', 3) +// CHECK: ('nundefsym', 0) +// CHECK: ('tocoff', 0) +// CHECK: ('ntoc', 0) +// CHECK: ('modtaboff', 0) +// CHECK: ('nmodtab', 0) +// CHECK: ('extrefsymoff', 0) +// CHECK: ('nextrefsyms', 0) +// CHECK: ('indirectsymoff', 0) +// CHECK: ('nindirectsyms', 0) +// CHECK: ('extreloff', 0) +// CHECK: ('nextrel', 0) +// CHECK: ('locreloff', 0) +// CHECK: ('nlocrel', 0) +// CHECK: ('_indirect_symbols', [ +// CHECK: ]) +// CHECK: ), +// CHECK: ])