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[DataLayout] Add isNullPointerAllZeroes #165314

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[DataLayout] Add isNullPointerAllZeroes #165314

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[DataLayout] Add isNullPointerAllZeroes
ro-i Oct 27, 2025
9113b53
move to getNullPointerValue
ro-i Oct 27, 2025
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6 changes: 6 additions & 0 deletions llvm/include/llvm/IR/DataLayout.h
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Original file line number Diff line number Diff line change
Expand Up @@ -398,6 +398,12 @@ class DataLayout {
PS.HasExternalState;
}

/// Returns if the null pointer for this address space has an all-zero bit
/// representation.
bool isNullPointerAllZeroes(unsigned AddrSpace) const {
return AddrSpace == 0;
}
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Your suggestion of getNullPointerValue() is probably better, could do something like the following?

Suggested change
bool isNullPointerAllZeroes(unsigned AddrSpace) const {
return AddrSpace == 0;
}
std::optional<APInt> getNullPointerValue(unsigned AS) const {
// Address space zero is currently defined to always have
// a all-zero null pointer representation, the others are
// target-specific and will require a data layout property.
// See https://discourse.llvm.org/t/rfc-introduce-sentinel-pointer-value-to-datalayout
if (AS == 0)
return 0;
return std::nullopt;
}

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That said, it probably doesn't matter too much what we use since it will have to change again for #131557 , the main thing I would like to see is avoiding ==0 checks which this patch achieves as is so IMO no need to do something generic.

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yup, see commit

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hm, race condition


/// Returns whether this address space has an "unstable" pointer
/// representation. The bitwise pattern of such pointers is allowed to change
/// in a target-specific way. For example, this could be used for copying
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9 changes: 9 additions & 0 deletions llvm/unittests/IR/DataLayoutTest.cpp
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Expand Up @@ -700,6 +700,15 @@ TEST(DataLayout, NonIntegralHelpers) {
}
}

TEST(DataLayoutTest, IsNullPointerAllZeroes) {
EXPECT_TRUE(DataLayout("").isNullPointerAllZeroes(0));
EXPECT_FALSE(DataLayout("").isNullPointerAllZeroes(1));
EXPECT_TRUE(DataLayout("p:32:32").isNullPointerAllZeroes(0));
EXPECT_FALSE(DataLayout("p:32:32").isNullPointerAllZeroes(1));
EXPECT_TRUE(DataLayout("p:64:64").isNullPointerAllZeroes(0));
EXPECT_FALSE(DataLayout("p:64:64").isNullPointerAllZeroes(1));
}

TEST(DataLayoutTest, CopyAssignmentInvalidatesStructLayout) {
DataLayout DL1 = cantFail(DataLayout::parse("p:32:32"));
DataLayout DL2 = cantFail(DataLayout::parse("p:64:64"));
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