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Allow targets to specify a minimum supported NOP size when performing NOP padding. If the desired padding is smaller than the supported NOP size,

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we will enlarge the padding to make it work.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@162870 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Owen Anderson 2012-08-29 22:18:56 +00:00
parent 66390805ad
commit 15b7a98ece
2 changed files with 13 additions and 0 deletions
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7
include/llvm/MC/MCAsmBackend.h
View File

@ -133,6 +133,13 @@ public:
/// @}
/// getMinimumNopSize - Returns the minimum size of a nop in bytes on this
/// target. The assembler will use this to emit excess padding in situations
/// where the padding required for simple alignment would be less than the
/// minimum nop size.
///
virtual unsigned getMinimumNopSize() const { return 1; }
/// writeNopData - Write an (optimal) nop sequence of Count bytes to the given
/// output. If the target cannot generate such a sequence, it should return an
/// error.

6
lib/MC/MCAssembler.cpp
View File

@ -325,6 +325,12 @@ uint64_t MCAssembler::computeFragmentSize(const MCAsmLayout &Layout,
const MCAlignFragment &AF = cast<MCAlignFragment>(F);
unsigned Offset = Layout.getFragmentOffset(&AF);
unsigned Size = OffsetToAlignment(Offset, AF.getAlignment());
// If we are padding with nops, force the padding to be larger than the
// minimum nop size.
if (Size > 0 && AF.hasEmitNops()) {
while (Size % getBackend().getMinimumNopSize())
Size += AF.getAlignment();
}
if (Size > AF.getMaxBytesToEmit())
return 0;
return Size;