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This is a patch to the assembler frontend to detect when aligning a text

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section with TextAlignFillValue and calls EmitCodeAlignment() instead of
calling EmitValueToAlignment().  This allows x86 assembly code to be aligned
with optimal nops.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@97158 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Kevin Enderby 2010-02-25 18:46:04 +00:00
parent 55c8a7e778
commit d74acb0c78
2 changed files with 165 additions and 3 deletions
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12
lib/MC/MCParser/AsmParser.cpp
View File

@ -146,7 +146,7 @@ bool AsmParser::Run() {
// FIXME: Target hook & command line option for initial section.
Out.SwitchSection(getMachOSection("__TEXT", "__text",
MCSectionMachO::S_ATTR_PURE_INSTRUCTIONS,
0, SectionKind()));
0, SectionKind::getText()));
// Prime the lexer.
@ -1237,8 +1237,14 @@ bool AsmParser::ParseDirectiveAlign(bool IsPow2, unsigned ValueSize) {
}
}
// FIXME: Target specific behavior about how the "extra" bytes are filled.
Out.EmitValueToAlignment(Alignment, FillExpr, ValueSize, MaxBytesToFill);
// FIXME: hard code the parser to use EmitCodeAlignment for text when using
// the TextAlignFillValue.
if(Out.getCurrentSection()->getKind().isText() &&
Lexer.getMAI().getTextAlignFillValue() == FillExpr)
Out.EmitCodeAlignment(Alignment, MaxBytesToFill);
else
// FIXME: Target specific behavior about how the "extra" bytes are filled.
Out.EmitValueToAlignment(Alignment, FillExpr, ValueSize, MaxBytesToFill);
return false;
}

156
test/MC/MachO/Darwin/optimal_nop.s Normal file
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@ -0,0 +1,156 @@
// Validate that we can assemble this file exactly like the platform
// assembler.
//
// RUN: llvm-mc -filetype=obj -triple i386-apple-darwin10 -o %t.mc.o %s
// RUN: as -arch i386 -o %t.as.o %s
// RUN: diff %t.mc.o %t.as.o
# 1 byte nop test
.align 4, 0 # start with 16 byte alignment filled with zeros
ret
# nop
# 0x90
.align 1, 0x90
ret
# 2 byte nop test
.align 4, 0 # start with 16 byte alignment filled with zeros
ret
ret
# xchg %ax,%ax
# 0x66, 0x90
.align 2, 0x90
ret
# 3 byte nop test
.align 4, 0 # start with 16 byte alignment filled with zeros
ret
# nopl (%[re]ax)
# 0x0f, 0x1f, 0x00
.align 2, 0x90
ret
# 4 byte nop test
.align 4, 0 # start with 16 byte alignment filled with zeros
ret
ret
ret
ret
# nopl 0(%[re]ax)
# 0x0f, 0x1f, 0x40, 0x00
.align 3, 0x90
ret
# 5 byte nop test
.align 4, 0 # start with 16 byte alignment filled with zeros
ret
ret
ret
# nopl 0(%[re]ax,%[re]ax,1)
# 0x0f, 0x1f, 0x44, 0x00, 0x00
.align 3, 0x90
ret
# 6 byte nop test
.align 4, 0 # start with 16 byte alignment filled with zeros
ret
ret
# nopw 0(%[re]ax,%[re]ax,1)
# 0x66, 0x0f, 0x1f, 0x44, 0x00, 0x00
.align 3, 0x90
ret
# 7 byte nop test
.align 4, 0 # start with 16 byte alignment filled with zeros
ret
# nopl 0L(%[re]ax)
# 0x0f, 0x1f, 0x80, 0x00, 0x00, 0x00, 0x00
.align 3, 0x90
ret
# 8 byte nop test
.align 4, 0 # start with 16 byte alignment filled with zeros
ret
ret
ret
ret
ret
ret
ret
ret
# nopl 0L(%[re]ax,%[re]ax,1)
# 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00
.align 3, 0x90
ret
# 9 byte nop test
.align 4, 0 # start with 16 byte alignment filled with zeros
ret
ret
ret
ret
ret
ret
ret
# nopw 0L(%[re]ax,%[re]ax,1)
# 0x66, 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00
.align 4, 0x90
ret
# 10 byte nop test
.align 4, 0 # start with 16 byte alignment filled with zeros
ret
ret
ret
ret
ret
ret
ret
# nopw %cs:0L(%[re]ax,%[re]ax,1)
# 0x66, 0x2e, 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00
.align 4, 0x90
ret
# 11 byte nop test
.align 4, 0 # start with 16 byte alignment filled with zeros
ret
ret
ret
ret
ret
# nopw %cs:0L(%[re]ax,%[re]ax,1)
# 0x66, 0x2e, 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00
.align 4, 0x90
ret
# 12 byte nop test
.align 4, 0 # start with 16 byte alignment filled with zeros
ret
ret
ret
ret
# nopw 0(%[re]ax,%[re]ax,1)
# nopw 0(%[re]ax,%[re]ax,1)
# 0x66, 0x0f, 0x1f, 0x44, 0x00, 0x00,
# 0x66, 0x0f, 0x1f, 0x44, 0x00, 0x00
.align 4, 0x90
ret
# 13 byte nop test
.align 4, 0 # start with 16 byte alignment filled with zeros
ret
ret
ret
# nopw 0(%[re]ax,%[re]ax,1)
# nopl 0L(%[re]ax)
# 0x66, 0x0f, 0x1f, 0x44, 0x00, 0x00,
# 0x0f, 0x1f, 0x80, 0x00, 0x00, 0x00, 0x00
.align 4, 0x90
ret
# 14 byte nop test
.align 4, 0 # start with 16 byte alignment filled with zeros
ret
ret
# nopl 0L(%[re]ax)
# nopl 0L(%[re]ax)
# 0x0f, 0x1f, 0x80, 0x00, 0x00, 0x00, 0x00,
# 0x0f, 0x1f, 0x80, 0x00, 0x00, 0x00, 0x00
.align 4, 0x90
ret
# 15 byte nop test
.align 4, 0 # start with 16 byte alignment filled with zeros
ret
# nopl 0L(%[re]ax)
# nopl 0L(%[re]ax,%[re]ax,1)
# 0x0f, 0x1f, 0x80, 0x00, 0x00, 0x00, 0x00,
# 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00
.align 4, 0x90
ret