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TargetRegisterInfo: Make the concept of imprecise lane masks explicit

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LaneMasks as given by getSubRegIndexLaneMask() have a limited number of
of bits, so for targets with more than 31 disjunct subregister there may
be cases where:

   getSubReg(Reg,A) does not overlap getSubReg(Reg,B)

but we still have

   (getSubRegIndexLaneMask(A) & getSubRegIndexLaneMask(B)) != 0.

I had hoped to keep this an implementation detail of the tablegen but as
my next commit shows we can avoid unnecessary imp-defs operands if we
know that the lane masks in use are precise.

This is in preparation to http://reviews.llvm.org/D10470.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239837 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Matthias Braun
2015-06-16 18:22:26 +00:00
parent 8e206c19f4
commit ff881427ec
2 changed files with 15 additions and 1 deletions
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13
include/llvm/Target/TargetRegisterInfo.h
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@@ -373,6 +373,19 @@ public:
return SubRegIndexLaneMasks[SubIdx];
}
/// Returns true if the given lane mask is imprecise.
///
/// LaneMasks as given by getSubRegIndexLaneMask() have a limited number of
/// bits, so for targets with more than 31 disjunct subregister indices there
/// may be cases where:
/// getSubReg(Reg,A) does not overlap getSubReg(Reg,B)
/// but we still have
/// (getSubRegIndexLaneMask(A) & getSubRegIndexLaneMask(B)) != 0.
/// This function returns true in those cases.
static bool isImpreciseLaneMask(unsigned LaneMask) {
return LaneMask & 0x80000000u;
}
/// The lane masks returned by getSubRegIndexLaneMask() above can only be
/// used to determine if sub-registers overlap - they can't be used to
/// determine if a set of sub-registers completely cover another