[llvm-commits] [llvm] r122043 - in /llvm/trunk: lib/MC/MCExpr.cpp test/MC/MachO/darwin-complex-difference.s
Jim Grosbach
grosbach at apple.com
Fri Dec 17 10:43:55 PST 2010
Very nice. I completely agree this is a good way to handle these sorts of oddball expressions. Thanks!
-Jim
On Dec 16, 2010, at 9:50 PM, Daniel Dunbar wrote:
> Author: ddunbar
> Date: Thu Dec 16 23:50:33 2010
> New Revision: 122043
>
> URL: http://llvm.org/viewvc/llvm-project?rev=122043&view=rev
> Log:
> 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
> --
>
> Added:
> llvm/trunk/test/MC/MachO/darwin-complex-difference.s
> Modified:
> llvm/trunk/lib/MC/MCExpr.cpp
>
> Modified: llvm/trunk/lib/MC/MCExpr.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/MC/MCExpr.cpp?rev=122043&r1=122042&r2=122043&view=diff
> ==============================================================================
> --- llvm/trunk/lib/MC/MCExpr.cpp (original)
> +++ llvm/trunk/lib/MC/MCExpr.cpp Thu Dec 16 23:50:33 2010
> @@ -271,6 +271,25 @@
> 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 @@
> // 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.
>
> Added: llvm/trunk/test/MC/MachO/darwin-complex-difference.s
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/MC/MachO/darwin-complex-difference.s?rev=122043&view=auto
> ==============================================================================
> --- llvm/trunk/test/MC/MachO/darwin-complex-difference.s (added)
> +++ llvm/trunk/test/MC/MachO/darwin-complex-difference.s Thu Dec 16 23:50:33 2010
> @@ -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: ])
>
>
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