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IRGen: Restore implicit truncation in some calls to llvm::APInt ctor #83842

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IRGen: Restore implicit truncation in some calls to llvm::APInt ctor #83842

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11 changes: 7 additions & 4 deletions lib/IRGen/GenCall.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2556,9 +2556,10 @@ llvm::Value *emitIndirectAsyncFunctionPointer(IRGenFunction &IGF,
llvm::Constant *One =
llvm::Constant::getIntegerValue(IntPtrTy, APInt(IntPtrTy->getBitWidth(),
1));
llvm::Constant *NegativeOne =
llvm::Constant::getIntegerValue(IntPtrTy, APInt(IntPtrTy->getBitWidth(),
-2));
// TODO: Avoid implicit truncation.
llvm::Constant *NegativeOne = llvm::Constant::getIntegerValue(
IntPtrTy, APInt(IntPtrTy->getBitWidth(), -2, /*isSigned*/ false,
/*implicitTrunc*/ true));
swift::irgen::Alignment PointerAlignment = IGF.IGM.getPointerAlignment();

llvm::Value *PtrToInt = IGF.Builder.CreatePtrToInt(pointer, IntPtrTy);
Expand Down Expand Up @@ -2587,8 +2588,10 @@ llvm::Value *emitIndirectCoroFunctionPointer(IRGenFunction &IGF,
IntPtrTy, APInt(IntPtrTy->getBitWidth(), 0));
llvm::Constant *One = llvm::Constant::getIntegerValue(
IntPtrTy, APInt(IntPtrTy->getBitWidth(), 1));
// TODO: Avoid implicit truncation.
llvm::Constant *NegativeOne = llvm::Constant::getIntegerValue(
IntPtrTy, APInt(IntPtrTy->getBitWidth(), -2));
IntPtrTy, APInt(IntPtrTy->getBitWidth(), -2, /*isSigned*/ false,
/*implicitTrunc*/ true));
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@rjmccall rjmccall Aug 21, 2025 •
edited
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This should pass /*isSigned*/ true. If IntPtrTy->getBitWidth() were actually huge, we would in fact want this to be sign-extended, and it also fixes the assertion without needing to pass implicitTrunc because it's okay to truncate consistent sign bits. (This also means you can just make the change on main.)

Also, I don't think this is on you to fix, but how did we end up with a variable called NegativeOne that represents a value of -2?

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Thanks!

how did we end up with a variable called NegativeOne that represents a value of -2

68bc33fed32#diff-e3cb1b9416734345839b90f1c5ec26d9173d335e687abb007c9ec0b332b3d3e4

cc @compnerd

swift::irgen::Alignment PointerAlignment = IGF.IGM.getPointerAlignment();

llvm::Value *PtrToInt = IGF.Builder.CreatePtrToInt(pointer, IntPtrTy);
Expand Down