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[flang] handle allocation of zero-sized objects #149165

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Merged
kkwli merged 2 commits into from
Jul 18, 2025
Merged

[flang] handle allocation of zero-sized objects #149165

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8ea361b
[flang] handle allocation of zero-sized objects
kkwli Jul 16, 2025
2bc33b5
update changes to address review comments
kkwli Jul 17, 2025
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16 changes: 13 additions & 3 deletions flang/lib/Optimizer/CodeGen/CodeGen.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1119,9 +1119,19 @@ struct AllocMemOpConversion : public fir::FIROpConversion<fir::AllocMemOp> {
mlir::Value size = genTypeSizeInBytes(loc, ity, rewriter, llvmObjectTy);
if (auto scaleSize = genAllocationScaleSize(heap, ity, rewriter))
size = rewriter.create<mlir::LLVM::MulOp>(loc, ity, size, scaleSize);
for (mlir::Value opnd : adaptor.getOperands())
size = rewriter.create<mlir::LLVM::MulOp>(
loc, ity, size, integerCast(loc, rewriter, ity, opnd));
for (mlir::Value opnd : adaptor.getOperands()) {
auto arg = integerCast(loc, rewriter, ity, opnd);
auto val = fir::getIntIfConstant(arg);
if (val && *val == 0) {
// As the return value of malloc(0) is implementation defined, allocate
// one byte to ensure the allocation status being true. This behavior
// aligns to what the runtime has.
size = genConstantIndex(loc, ity, rewriter, 1);
break;
} else {
size = rewriter.create<mlir::LLVM::MulOp>(loc, ity, size, arg);
}
}
auto mallocTyWidth = lowerTy().getIndexTypeBitwidth();
auto mallocTy =
mlir::IntegerType::get(rewriter.getContext(), mallocTyWidth);
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37 changes: 37 additions & 0 deletions flang/test/Lower/zero-size2.f90
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@@ -0,0 +1,37 @@
! RUN: %flang_fc1 -emit-llvm -o - %s | FileCheck %s

subroutine sub1()
integer, allocatable :: arr(:)
allocate(arr(0))
! CHECK-LABEL: @sub1_
! CHECK: %[[p:.*]] = call ptr @malloc(i64 1)
end

subroutine sub2()
real, allocatable :: arr(:,:)
allocate(arr(10,0))
! CHECK-LABEL: @sub2_
! CHECK: %[[p:.*]] = call ptr @malloc(i64 1)
end

subroutine sub3(i)
integer :: i
real, allocatable :: arr(:,:)
allocate(arr(i,0))
! CHECK-LABEL: @sub3_
! CHECK: %[[p:.*]] = call ptr @malloc(i64 1)
end

subroutine sub4()
character(:), allocatable :: c
allocate(character(0)::c)
! CHECK-LABEL: @sub4_
! CHECK: %[[p:.*]] = call ptr @malloc(i64 1)
end

subroutine sub5()
character(:), allocatable :: c(:)
allocate(character(5)::c(0))
! CHECK-LABEL: @sub5_
! CHECK: %[[p:.*]] = call ptr @malloc(i64 1)
end
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