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Return undef on FP <-> Int conversions that overflow (PR21330).
The LLVM Lang Ref states for signed/unsigned int to float conversions: "If the value cannot fit in the floating point value, the results are undefined." And for FP to signed/unsigned int: "If the value cannot fit in ty2, the results are undefined." This matches the C definitions. The existing behavior pins to infinity or a max int value, but that may just lead to more confusion as seen in: http://llvm.org/bugs/show_bug.cgi?id=21130 Returning undef will hopefully lead to a less silent failure. Differential Revision: http://reviews.llvm.org/D5603 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219542 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -593,8 +593,13 @@ Constant *llvm::ConstantFoldCastInstruction(unsigned opc, Constant *V,
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bool ignored;
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uint64_t x[2];
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uint32_t DestBitWidth = cast<IntegerType>(DestTy)->getBitWidth();
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(void) V.convertToInteger(x, DestBitWidth, opc==Instruction::FPToSI,
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APFloat::rmTowardZero, &ignored);
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if (APFloat::opInvalidOp ==
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V.convertToInteger(x, DestBitWidth, opc==Instruction::FPToSI,
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APFloat::rmTowardZero, &ignored)) {
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// Undefined behavior invoked - the destination type can't represent
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// the input constant.
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return UndefValue::get(DestTy);
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}
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APInt Val(DestBitWidth, x);
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return ConstantInt::get(FPC->getContext(), Val);
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}
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@ -653,9 +658,13 @@ Constant *llvm::ConstantFoldCastInstruction(unsigned opc, Constant *V,
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APInt api = CI->getValue();
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APFloat apf(DestTy->getFltSemantics(),
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APInt::getNullValue(DestTy->getPrimitiveSizeInBits()));
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(void)apf.convertFromAPInt(api,
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opc==Instruction::SIToFP,
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APFloat::rmNearestTiesToEven);
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if (APFloat::opOverflow &
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apf.convertFromAPInt(api, opc==Instruction::SIToFP,
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APFloat::rmNearestTiesToEven)) {
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// Undefined behavior invoked - the destination type can't represent
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// the input constant.
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return UndefValue::get(DestTy);
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}
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return ConstantFP::get(V->getContext(), apf);
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}
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return nullptr;
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@ -1050,3 +1050,37 @@ define i8 @test85(i32 %a) {
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; CHECK: [[SHR:%.*]] = lshr exact i32 [[ADD]], 23
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; CHECK: [[CST:%.*]] = trunc i32 [[SHR]] to i8
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}
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; Overflow on a float to int or int to float conversion is undefined (PR21130).
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define i8 @overflow_fptosi() {
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%i = fptosi double 1.56e+02 to i8
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ret i8 %i
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; CHECK-LABEL: @overflow_fptosi(
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; CHECK-NEXT: ret i8 undef
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}
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define i8 @overflow_fptoui() {
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%i = fptoui double 2.56e+02 to i8
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ret i8 %i
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; CHECK-LABEL: @overflow_fptoui(
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; CHECK-NEXT: ret i8 undef
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}
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; The maximum float is approximately 2 ** 128 which is 3.4E38.
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; The constant below is 4E38. Use a 130 bit integer to hold that
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; number; 129-bits for the value + 1 bit for the sign.
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define float @overflow_uitofp() {
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%i = uitofp i130 400000000000000000000000000000000000000 to float
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ret float %i
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; CHECK-LABEL: @overflow_uitofp(
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; CHECK-NEXT: ret float undef
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}
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define float @overflow_sitofp() {
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%i = sitofp i130 400000000000000000000000000000000000000 to float
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ret float %i
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; CHECK-LABEL: @overflow_sitofp(
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; CHECK-NEXT: ret float undef
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}
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