[IR] Add ImplicitTrunc argument to ConstantInt::get() #170865
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Add an ImplicitTrunc argument to ConstantInt::get(), which allows controlling whether implicit truncation of the value is permitted. This argument currently defaults to true, but will be switched to false in the future to guard against signed/unsigned confusion, similar to what has already happened for APInt. The argument gives an opt-out for cases where the truncation is intended. The patch contains one illustrative example where this happens.
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@llvm/pr-subscribers-llvm-transforms @llvm/pr-subscribers-llvm-ir Author: Nikita Popov (nikic) ChangesAdd an ImplicitTrunc argument to ConstantInt::get(), which allows controlling whether implicit truncation of the value is permitted. This argument currently defaults to true, but will be switched to false in the future to guard against signed/unsigned confusion, similar to what has already happened for APInt. The argument gives an opt-out for cases where the truncation is intended. The patch contains one illustrative example where this happens. Full diff: https://github.com/llvm/llvm-project/pull/170865.diff 3 Files Affected:
diff --git a/llvm/include/llvm/IR/Constants.h b/llvm/include/llvm/IR/Constants.h
index e3f2eb9fa44b8..d03c8851616df 100644
--- a/llvm/include/llvm/IR/Constants.h
+++ b/llvm/include/llvm/IR/Constants.h
@@ -112,16 +112,21 @@ class ConstantInt final : public ConstantData {
/// If Ty is a vector type, return a Constant with a splat of the given
/// value. Otherwise return a ConstantInt for the given value.
- LLVM_ABI static Constant *get(Type *Ty, uint64_t V, bool IsSigned = false);
+ /// \param ImplicitTrunc Whether to allow implicit truncation of the value.
+ // TODO: Make ImplicitTrunc default to false.
+ LLVM_ABI static Constant *get(Type *Ty, uint64_t V, bool IsSigned = false,
+ bool ImplicitTrunc = true);
/// Return a ConstantInt with the specified integer value for the specified
/// type. If the type is wider than 64 bits, the value will be zero-extended
/// to fit the type, unless IsSigned is true, in which case the value will
/// be interpreted as a 64-bit signed integer and sign-extended to fit
/// the type.
- /// Get a ConstantInt for a specific value.
+ /// \param ImplicitTrunc Whether to allow implicit truncation of the value.
+ // TODO: Make ImplicitTrunc default to false.
LLVM_ABI static ConstantInt *get(IntegerType *Ty, uint64_t V,
- bool IsSigned = false);
+ bool IsSigned = false,
+ bool ImplicitTrunc = true);
/// Return a ConstantInt with the specified value for the specified type. The
/// value V will be canonicalized to a an unsigned APInt. Accessing it with
diff --git a/llvm/lib/IR/Constants.cpp b/llvm/lib/IR/Constants.cpp
index 6b82da140256f..2f020274c305a 100644
--- a/llvm/lib/IR/Constants.cpp
+++ b/llvm/lib/IR/Constants.cpp
@@ -960,8 +960,10 @@ ConstantInt *ConstantInt::get(LLVMContext &Context, ElementCount EC,
return Slot.get();
}
-Constant *ConstantInt::get(Type *Ty, uint64_t V, bool isSigned) {
- Constant *C = get(cast<IntegerType>(Ty->getScalarType()), V, isSigned);
+Constant *ConstantInt::get(Type *Ty, uint64_t V, bool IsSigned,
+ bool ImplicitTrunc) {
+ Constant *C =
+ get(cast<IntegerType>(Ty->getScalarType()), V, IsSigned, ImplicitTrunc);
// For vectors, broadcast the value.
if (VectorType *VTy = dyn_cast<VectorType>(Ty))
@@ -970,11 +972,10 @@ Constant *ConstantInt::get(Type *Ty, uint64_t V, bool isSigned) {
return C;
}
-ConstantInt *ConstantInt::get(IntegerType *Ty, uint64_t V, bool isSigned) {
- // TODO: Avoid implicit trunc?
- // See https://github.com/llvm/llvm-project/issues/112510.
+ConstantInt *ConstantInt::get(IntegerType *Ty, uint64_t V, bool IsSigned,
+ bool ImplicitTrunc) {
return get(Ty->getContext(),
- APInt(Ty->getBitWidth(), V, isSigned, /*implicitTrunc=*/true));
+ APInt(Ty->getBitWidth(), V, IsSigned, ImplicitTrunc));
}
Constant *ConstantInt::get(Type *Ty, const APInt& V) {
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index 743c4f574e131..8e7282a4ffefe 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -3811,7 +3811,9 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
if (VecToReduceCount.isFixed()) {
unsigned VectorSize = VecToReduceCount.getFixedValue();
return BinaryOperator::CreateMul(
- Splat, ConstantInt::get(Splat->getType(), VectorSize));
+ Splat,
+ ConstantInt::get(Splat->getType(), VectorSize, /*IsSigned=*/false,
+ /*ImplicitTrunc=*/true));
}
}
}
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dtcxzyw
approved these changes
Dec 5, 2025
🐧 Linux x64 Test Results
✅ The build succeeded and all tests passed. |
Co-authored-by: Yingwei Zheng <dtcxzyw@qq.com>
Collaborator
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LLVM Buildbot has detected a new failure on builder Full details are available at: https://lab.llvm.org/buildbot/#/builders/169/builds/17790 Here is the relevant piece of the build log for the reference |
honeygoyal
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to honeygoyal/llvm-project
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Dec 9, 2025
Add an ImplicitTrunc argument to ConstantInt::get(), which allows
controlling whether implicit truncation of the value is permitted.
This argument currently defaults to true, but will be switched to false
in the future to guard against signed/unsigned confusion, similar to
what has already happened for APInt.
The argument gives an opt-out for cases where the truncation is
intended. The patch contains one illustrative example where this
happens.
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Add an ImplicitTrunc argument to ConstantInt::get(), which allows controlling whether implicit truncation of the value is permitted.
This argument currently defaults to true, but will be switched to false in the future to guard against signed/unsigned confusion, similar to what has already happened for APInt.
The argument gives an opt-out for cases where the truncation is intended. The patch contains one illustrative example where this happens.