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[WebAssembly] Use absolute pointers #31676

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[WebAssembly] Use absolute pointers #31676

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9b94510
[WebAssembly] Use absolute pointers #ifdef __WASM__
MaxDesiatov May 9, 2020
74a6536
Add support for Wasm absolute pointers in IRGen
MaxDesiatov Aug 8, 2021
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14 changes: 14 additions & 0 deletions include/swift/Basic/RelativePointer.h
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Original file line number Diff line number Diff line change
Expand Up @@ -146,6 +146,12 @@ static inline uintptr_t applyRelativeOffset(BasePtrTy *basePtr, Offset offset) {
std::is_signed<Offset>::value,
"offset type should be signed integer");

#if defined(__WASM__)
// WebAssembly target uses only absolute pointers.
// See https://forums.swift.org/t/wasm-support/16087/17 for more details.
return (uintptr_t)(intptr_t)offset;
#endif

auto base = reinterpret_cast<uintptr_t>(basePtr);
// We want to do wrapping arithmetic, but with a sign-extended
// offset. To do this in C, we need to do signed promotion to get
Expand All @@ -165,6 +171,14 @@ static inline Offset measureRelativeOffset(A *referent, B *base) {
std::is_signed<Offset>::value,
"offset type should be signed integer");

#if defined(__WASM__)
// WebAssembly target uses only absolute pointers.
auto offset = (Offset)(uintptr_t)referent;
assert((intptr_t)offset == (intptr_t)(uintptr_t)referent
&& "pointer too large to fit in offset type");
return offset;
#endif

auto distance = (uintptr_t)referent - (uintptr_t)base;
// Truncate as unsigned, then wrap around to signed.
auto truncatedDistance =
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9 changes: 9 additions & 0 deletions lib/IRGen/IRGenFunction.cpp
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Expand Up @@ -319,6 +319,15 @@ IRGenFunction::emitLoadOfRelativePointer(Address addr, bool isFar,
if (!isFar) {
value = Builder.CreateSExt(value, IGM.IntPtrTy);
}
// WebAssembly target uses only absolute pointers.
// See https://forums.swift.org/t/wasm-support/16087/17 for more details.
if (IGM.TargetInfo.OutputObjectFormat == llvm::Triple::Wasm) {
auto *uncastPointer = Builder.CreateIntToPtr(value, IGM.Int8PtrTy);
auto uncastPointerAddress = Address(uncastPointer, IGM.getPointerAlignment());
auto pointer = Builder.CreateBitCast(uncastPointerAddress, expectedType);
return pointer.getAddress();
}

auto *addrInt = Builder.CreatePtrToInt(addr.getAddress(), IGM.IntPtrTy);
auto *uncastPointerInt = Builder.CreateAdd(addrInt, value);
auto *uncastPointer = Builder.CreateIntToPtr(uncastPointerInt, IGM.Int8PtrTy);
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