[clang] d6b0af0 - [clang][Interp] Add more shift error checking
Timm Bäder via cfe-commits
cfe-commits at lists.llvm.org
Thu Jul 20 06:36:09 PDT 2023
Author: Timm Bäder
Date: 2023-07-20T15:35:47+02:00
New Revision: d6b0af0574ca21ae7b0fa6aa364345159f451da1
URL: https://github.com/llvm/llvm-project/commit/d6b0af0574ca21ae7b0fa6aa364345159f451da1
DIFF: https://github.com/llvm/llvm-project/commit/d6b0af0574ca21ae7b0fa6aa364345159f451da1.diff
LOG: [clang][Interp] Add more shift error checking
Differential Revision: https://reviews.llvm.org/D150209
Added:
Modified:
clang/lib/AST/Interp/Integral.h
clang/lib/AST/Interp/Interp.h
clang/test/AST/Interp/shifts.cpp
Removed:
################################################################################
diff --git a/clang/lib/AST/Interp/Integral.h b/clang/lib/AST/Interp/Integral.h
index cc7c7a9d2430ee..de588ab8c9f191 100644
--- a/clang/lib/AST/Interp/Integral.h
+++ b/clang/lib/AST/Interp/Integral.h
@@ -127,7 +127,11 @@ template <unsigned Bits, bool Signed> class Integral final {
return Compare(V, RHS.V);
}
- unsigned countLeadingZeros() const { return llvm::countl_zero<ReprT>(V); }
+ unsigned countLeadingZeros() const {
+ if constexpr (!Signed)
+ return llvm::countl_zero<ReprT>(V);
+ llvm_unreachable("Don't call countLeadingZeros() on signed types.");
+ }
Integral truncate(unsigned TruncBits) const {
if (TruncBits >= Bits)
diff --git a/clang/lib/AST/Interp/Interp.h b/clang/lib/AST/Interp/Interp.h
index d70b732f6fd865..15112001536650 100644
--- a/clang/lib/AST/Interp/Interp.h
+++ b/clang/lib/AST/Interp/Interp.h
@@ -105,8 +105,9 @@ bool CheckPure(InterpState &S, CodePtr OpPC, const CXXMethodDecl *MD);
bool CheckCtorCall(InterpState &S, CodePtr OpPC, const Pointer &This);
/// Checks if the shift operation is legal.
-template <typename RT>
-bool CheckShift(InterpState &S, CodePtr OpPC, const RT &RHS, unsigned Bits) {
+template <typename LT, typename RT>
+bool CheckShift(InterpState &S, CodePtr OpPC, const LT &LHS, const RT &RHS,
+ unsigned Bits) {
if (RHS.isNegative()) {
const SourceInfo &Loc = S.Current->getSource(OpPC);
S.CCEDiag(Loc, diag::note_constexpr_negative_shift) << RHS.toAPSInt();
@@ -122,6 +123,20 @@ bool CheckShift(InterpState &S, CodePtr OpPC, const RT &RHS, unsigned Bits) {
S.CCEDiag(E, diag::note_constexpr_large_shift) << Val << Ty << Bits;
return false;
}
+
+ if (LHS.isSigned() && !S.getLangOpts().CPlusPlus20) {
+ const Expr *E = S.Current->getExpr(OpPC);
+ // C++11 [expr.shift]p2: A signed left shift must have a non-negative
+ // operand, and must not overflow the corresponding unsigned type.
+ if (LHS.isNegative())
+ S.CCEDiag(E, diag::note_constexpr_lshift_of_negative) << LHS.toAPSInt();
+ else if (LHS.toUnsigned().countLeadingZeros() < static_cast<unsigned>(RHS))
+ S.CCEDiag(E, diag::note_constexpr_lshift_discards);
+ }
+
+ // C++2a [expr.shift]p2: [P0907R4]:
+ // E1 << E2 is the unique value congruent to
+ // E1 x 2^E2 module 2^N.
return true;
}
@@ -1523,7 +1538,7 @@ inline bool Shr(InterpState &S, CodePtr OpPC) {
const auto &LHS = S.Stk.pop<LT>();
const unsigned Bits = LHS.bitWidth();
- if (!CheckShift<RT>(S, OpPC, RHS, Bits))
+ if (!CheckShift(S, OpPC, LHS, RHS, Bits))
return false;
Integral<LT::bitWidth(), false> R;
@@ -1540,7 +1555,7 @@ inline bool Shl(InterpState &S, CodePtr OpPC) {
const auto &LHS = S.Stk.pop<LT>();
const unsigned Bits = LHS.bitWidth();
- if (!CheckShift<RT>(S, OpPC, RHS, Bits))
+ if (!CheckShift(S, OpPC, LHS, RHS, Bits))
return false;
Integral<LT::bitWidth(), false> R;
diff --git a/clang/test/AST/Interp/shifts.cpp b/clang/test/AST/Interp/shifts.cpp
index 3b2fc2619fe355..cf71e7145c2742 100644
--- a/clang/test/AST/Interp/shifts.cpp
+++ b/clang/test/AST/Interp/shifts.cpp
@@ -152,4 +152,39 @@ namespace shifts {
constexpr signed int R = (sizeof(unsigned) * 8) + 1;
constexpr decltype(L) M = (R > 32 && R < 64) ? L << R : 0;
constexpr decltype(L) M2 = (R > 32 && R < 64) ? L >> R : 0;
+
+
+ constexpr int signedShift() { // cxx17-error {{never produces a constant expression}} \
+ // ref-cxx17-error {{never produces a constant expression}}
+ return 1024 << 31; // cxx17-warning {{signed shift result}} \
+ // ref-cxx17-warning {{signed shift result}} \
+ // cxx17-note {{signed left shift discards bits}} \
+ // ref-cxx17-note {{signed left shift discards bits}}
+ }
+
+ constexpr int negativeShift() { // cxx17-error {{never produces a constant expression}} \
+ // ref-cxx17-error {{never produces a constant expression}}
+ return -1 << 2; // cxx17-warning {{shifting a negative signed value is undefined}} \
+ // ref-cxx17-warning {{shifting a negative signed value is undefined}} \
+ // cxx17-note {{left shift of negative value -1}} \
+ // ref-cxx17-note {{left shift of negative value -1}}
+ }
+
+ constexpr int foo(int a) {
+ return -a << 2; // cxx17-note {{left shift of negative value -10}} \
+ // ref-cxx17-note {{left shift of negative value -10}} \
+ // cxx17-note {{left shift of negative value -2}} \
+ // ref-cxx17-note {{left shift of negative value -2}}
+ }
+ static_assert(foo(10)); // cxx17-error {{not an integral constant expression}} \
+ // cxx17-note {{in call to 'foo(10)'}} \
+ // ref-cxx17-error {{not an integral constant expression}} \
+ // ref-cxx17-note {{in call to 'foo(10)'}}
+
+ constexpr int a = -2;
+ static_assert(foo(a));
+ static_assert(foo(-a)); // cxx17-error {{not an integral constant expression}} \
+ // cxx17-note {{in call to 'foo(2)'}} \
+ // ref-cxx17-error {{not an integral constant expression}} \
+ // ref-cxx17-note {{in call to 'foo(2)'}}
};
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