[llvm-branch-commits] [clang] release/19.x: [ExprConstant] Handle shift overflow the same way as other kinds of overflow (#99579) (PR #100452)
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Wed Jul 24 12:45:10 PDT 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-clang
Author: None (llvmbot)
<details>
<summary>Changes</summary>
Backport 20eff68
Requested by: @<!-- -->efriedma-quic
---
Full diff: https://github.com/llvm/llvm-project/pull/100452.diff
8 Files Affected:
- (modified) clang/docs/ReleaseNotes.rst (+2)
- (modified) clang/lib/AST/ExprConstant.cpp (+17-9)
- (modified) clang/lib/AST/Interp/Interp.h (+14-8)
- (modified) clang/lib/Sema/SemaExpr.cpp (+2-1)
- (modified) clang/test/CXX/basic/basic.types/p10.cpp (+1-1)
- (modified) clang/test/Sema/constant-builtins-2.c (+4-8)
- (modified) clang/test/SemaCXX/class.cpp (+8-1)
- (modified) clang/test/SemaCXX/enum.cpp (+17-7)
``````````diff
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 5b6ee9830b507..549da6812740f 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -765,6 +765,8 @@ Improvements to Clang's diagnostics
UsingWithAttr<int> objUsingWA; // warning: 'UsingWithAttr' is deprecated
+- Clang now diagnoses undefined behavior in constant expressions more consistently. This includes invalid shifts, and signed overflow in arithmetic.
+
Improvements to Clang's time-trace
----------------------------------
diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index 03a606102a77e..5e57b5e8bc8f1 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -2839,6 +2839,8 @@ static bool handleIntIntBinOp(EvalInfo &Info, const BinaryOperator *E,
// During constant-folding, a negative shift is an opposite shift. Such
// a shift is not a constant expression.
Info.CCEDiag(E, diag::note_constexpr_negative_shift) << RHS;
+ if (!Info.noteUndefinedBehavior())
+ return false;
RHS = -RHS;
goto shift_right;
}
@@ -2849,19 +2851,23 @@ static bool handleIntIntBinOp(EvalInfo &Info, const BinaryOperator *E,
if (SA != RHS) {
Info.CCEDiag(E, diag::note_constexpr_large_shift)
<< RHS << E->getType() << LHS.getBitWidth();
+ if (!Info.noteUndefinedBehavior())
+ return false;
} else if (LHS.isSigned() && !Info.getLangOpts().CPlusPlus20) {
// C++11 [expr.shift]p2: A signed left shift must have a non-negative
// operand, and must not overflow the corresponding unsigned type.
// C++2a [expr.shift]p2: E1 << E2 is the unique value congruent to
// E1 x 2^E2 module 2^N.
- if (LHS.isNegative())
+ if (LHS.isNegative()) {
Info.CCEDiag(E, diag::note_constexpr_lshift_of_negative) << LHS;
- else if (LHS.countl_zero() < SA)
+ if (!Info.noteUndefinedBehavior())
+ return false;
+ } else if (LHS.countl_zero() < SA) {
Info.CCEDiag(E, diag::note_constexpr_lshift_discards);
+ if (!Info.noteUndefinedBehavior())
+ return false;
+ }
}
- if (Info.EvalStatus.Diag && !Info.EvalStatus.Diag->empty() &&
- Info.getLangOpts().CPlusPlus11)
- return false;
Result = LHS << SA;
return true;
}
@@ -2875,6 +2881,8 @@ static bool handleIntIntBinOp(EvalInfo &Info, const BinaryOperator *E,
// During constant-folding, a negative shift is an opposite shift. Such a
// shift is not a constant expression.
Info.CCEDiag(E, diag::note_constexpr_negative_shift) << RHS;
+ if (!Info.noteUndefinedBehavior())
+ return false;
RHS = -RHS;
goto shift_left;
}
@@ -2882,13 +2890,13 @@ static bool handleIntIntBinOp(EvalInfo &Info, const BinaryOperator *E,
// C++11 [expr.shift]p1: Shift width must be less than the bit width of the
// shifted type.
unsigned SA = (unsigned) RHS.getLimitedValue(LHS.getBitWidth()-1);
- if (SA != RHS)
+ if (SA != RHS) {
Info.CCEDiag(E, diag::note_constexpr_large_shift)
<< RHS << E->getType() << LHS.getBitWidth();
+ if (!Info.noteUndefinedBehavior())
+ return false;
+ }
- if (Info.EvalStatus.Diag && !Info.EvalStatus.Diag->empty() &&
- Info.getLangOpts().CPlusPlus11)
- return false;
Result = LHS >> SA;
return true;
}
diff --git a/clang/lib/AST/Interp/Interp.h b/clang/lib/AST/Interp/Interp.h
index 8e96f78d90568..253a433e7340a 100644
--- a/clang/lib/AST/Interp/Interp.h
+++ b/clang/lib/AST/Interp/Interp.h
@@ -153,7 +153,8 @@ bool CheckShift(InterpState &S, CodePtr OpPC, const LT &LHS, const RT &RHS,
if (RHS.isNegative()) {
const SourceInfo &Loc = S.Current->getSource(OpPC);
S.CCEDiag(Loc, diag::note_constexpr_negative_shift) << RHS.toAPSInt();
- return false;
+ if (!S.noteUndefinedBehavior())
+ return false;
}
// C++11 [expr.shift]p1: Shift width must be less than the bit width of
@@ -163,17 +164,24 @@ bool CheckShift(InterpState &S, CodePtr OpPC, const LT &LHS, const RT &RHS,
const APSInt Val = RHS.toAPSInt();
QualType Ty = E->getType();
S.CCEDiag(E, diag::note_constexpr_large_shift) << Val << Ty << Bits;
- return !(S.getEvalStatus().Diag && !S.getEvalStatus().Diag->empty() && S.getLangOpts().CPlusPlus11);
+ if (!S.noteUndefinedBehavior())
+ 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())
+ if (LHS.isNegative()) {
S.CCEDiag(E, diag::note_constexpr_lshift_of_negative) << LHS.toAPSInt();
- else if (LHS.toUnsigned().countLeadingZeros() < static_cast<unsigned>(RHS))
+ if (!S.noteUndefinedBehavior())
+ return false;
+ } else if (LHS.toUnsigned().countLeadingZeros() <
+ static_cast<unsigned>(RHS)) {
S.CCEDiag(E, diag::note_constexpr_lshift_discards);
+ if (!S.noteUndefinedBehavior())
+ return false;
+ }
}
// C++2a [expr.shift]p2: [P0907R4]:
@@ -2269,8 +2277,7 @@ inline bool DoShift(InterpState &S, CodePtr OpPC, LT &LHS, RT &RHS) {
// shift is not a constant expression.
const SourceInfo &Loc = S.Current->getSource(OpPC);
S.CCEDiag(Loc, diag::note_constexpr_negative_shift) << RHS.toAPSInt();
- if (S.getLangOpts().CPlusPlus11 && S.getEvalStatus().Diag &&
- !S.getEvalStatus().Diag->empty())
+ if (!S.noteUndefinedBehavior())
return false;
RHS = -RHS;
return DoShift < LT, RT,
@@ -2286,8 +2293,7 @@ inline bool DoShift(InterpState &S, CodePtr OpPC, LT &LHS, RT &RHS) {
// E1 x 2^E2 module 2^N.
const SourceInfo &Loc = S.Current->getSource(OpPC);
S.CCEDiag(Loc, diag::note_constexpr_lshift_of_negative) << LHS.toAPSInt();
- if (S.getLangOpts().CPlusPlus11 && S.getEvalStatus().Diag &&
- !S.getEvalStatus().Diag->empty())
+ if (!S.noteUndefinedBehavior())
return false;
}
}
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 9207bf7a41349..da5f5fbdafba0 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -17046,7 +17046,8 @@ Sema::VerifyIntegerConstantExpression(Expr *E, llvm::APSInt *Result,
// not a constant expression as a side-effect.
bool Folded =
E->EvaluateAsRValue(EvalResult, Context, /*isConstantContext*/ true) &&
- EvalResult.Val.isInt() && !EvalResult.HasSideEffects;
+ EvalResult.Val.isInt() && !EvalResult.HasSideEffects &&
+ (!getLangOpts().CPlusPlus || !EvalResult.HasUndefinedBehavior);
if (!isa<ConstantExpr>(E))
E = ConstantExpr::Create(Context, E, EvalResult.Val);
diff --git a/clang/test/CXX/basic/basic.types/p10.cpp b/clang/test/CXX/basic/basic.types/p10.cpp
index a543f248e5371..92d6da0035ea5 100644
--- a/clang/test/CXX/basic/basic.types/p10.cpp
+++ b/clang/test/CXX/basic/basic.types/p10.cpp
@@ -142,7 +142,7 @@ constexpr int arb(int n) { // expected-note {{declared here}}
expected-note {{function parameter 'n' with unknown value cannot be used in a constant expression}}
}
constexpr long Overflow[(1 << 30) << 2]{}; // expected-warning {{requires 34 bits to represent}} \
- expected-warning {{variable length array folded to constant array as an extension}} \
+ expected-error {{variable length array declaration not allowed at file scope}} \
expected-warning {{variable length arrays in C++ are a Clang extension}} \
expected-note {{signed left shift discards bits}}
diff --git a/clang/test/Sema/constant-builtins-2.c b/clang/test/Sema/constant-builtins-2.c
index 00767267cd6c2..37b63cf4f6b32 100644
--- a/clang/test/Sema/constant-builtins-2.c
+++ b/clang/test/Sema/constant-builtins-2.c
@@ -265,10 +265,8 @@ char clz52[__builtin_clzg((unsigned __int128)0x1) == BITSIZE(__int128) - 1 ? 1 :
char clz53[__builtin_clzg((unsigned __int128)0x1, 42) == BITSIZE(__int128) - 1 ? 1 : -1];
char clz54[__builtin_clzg((unsigned __int128)0xf) == BITSIZE(__int128) - 4 ? 1 : -1];
char clz55[__builtin_clzg((unsigned __int128)0xf, 42) == BITSIZE(__int128) - 4 ? 1 : -1];
-char clz56[__builtin_clzg((unsigned __int128)(1 << (BITSIZE(__int128) - 1))) == 0 ? 1 : -1]; // expected-warning {{variable length array folded to constant array as an extension}}
- // expected-note at -1 {{shift count 127 >= width of type 'int' (32 bits)}}
-char clz57[__builtin_clzg((unsigned __int128)(1 << (BITSIZE(__int128) - 1)), 42) == 0 ? 1 : -1]; // expected-warning {{variable length array folded to constant array as an extension}}
- // expected-note at -1 {{shift count 127 >= width of type 'int' (32 bits)}}
+char clz56[__builtin_clzg((unsigned __int128)(1 << (BITSIZE(__int128) - 1))) == 0 ? 1 : -1]; // expected-error {{variable length array declaration not allowed at file scope}}
+char clz57[__builtin_clzg((unsigned __int128)(1 << (BITSIZE(__int128) - 1)), 42) == 0 ? 1 : -1]; // expected-error {{variable length array declaration not allowed at file scope}}
#endif
int clz58 = __builtin_clzg((unsigned _BitInt(128))0); // expected-error {{not a compile-time constant}}
char clz59[__builtin_clzg((unsigned _BitInt(128))0, 42) == 42 ? 1 : -1];
@@ -276,10 +274,8 @@ char clz60[__builtin_clzg((unsigned _BitInt(128))0x1) == BITSIZE(_BitInt(128)) -
char clz61[__builtin_clzg((unsigned _BitInt(128))0x1, 42) == BITSIZE(_BitInt(128)) - 1 ? 1 : -1];
char clz62[__builtin_clzg((unsigned _BitInt(128))0xf) == BITSIZE(_BitInt(128)) - 4 ? 1 : -1];
char clz63[__builtin_clzg((unsigned _BitInt(128))0xf, 42) == BITSIZE(_BitInt(128)) - 4 ? 1 : -1];
-char clz64[__builtin_clzg((unsigned _BitInt(128))(1 << (BITSIZE(_BitInt(128)) - 1))) == 0 ? 1 : -1]; // expected-warning {{variable length array folded to constant array as an extension}}
- // expected-note at -1 {{shift count 127 >= width of type 'int' (32 bits)}}
-char clz65[__builtin_clzg((unsigned _BitInt(128))(1 << (BITSIZE(_BitInt(128)) - 1)), 42) == 0 ? 1 : -1]; // expected-warning {{variable length array folded to constant array as an extension}}
- // expected-note at -1 {{shift count 127 >= width of type 'int' (32 bits)}}
+char clz64[__builtin_clzg((unsigned _BitInt(128))(1 << (BITSIZE(_BitInt(128)) - 1))) == 0 ? 1 : -1]; // expected-error {{variable length array declaration not allowed at file scope}}
+char clz65[__builtin_clzg((unsigned _BitInt(128))(1 << (BITSIZE(_BitInt(128)) - 1)), 42) == 0 ? 1 : -1]; // expected-error {{variable length array declaration not allowed at file scope}}
char ctz1[__builtin_ctz(1) == 0 ? 1 : -1];
char ctz2[__builtin_ctz(8) == 3 ? 1 : -1];
diff --git a/clang/test/SemaCXX/class.cpp b/clang/test/SemaCXX/class.cpp
index f874b7be2b70e..2f59544e7f36c 100644
--- a/clang/test/SemaCXX/class.cpp
+++ b/clang/test/SemaCXX/class.cpp
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -fsyntax-only -verify -Wc++11-compat %s
+// RUN: %clang_cc1 -fsyntax-only -verify=expected,cxx11 -Wc++11-compat %s
// RUN: %clang_cc1 -fsyntax-only -verify -Wc++11-compat %s -std=c++98
class C {
public:
@@ -55,6 +55,13 @@ class C {
// expected-error at -2 {{static const volatile data member must be initialized out of line}}
#endif
static const E evi = 0;
+ static const int overflow = 1000000*1000000; // cxx11-error {{in-class initializer for static data member is not a constant expression}}
+ // expected-warning at -1 {{overflow in expression}}
+ static const int overflow_shift = 1<<32; // cxx11-error {{in-class initializer for static data member is not a constant expression}}
+ static const int overflow_shift2 = 1>>32; // cxx11-error {{in-class initializer for static data member is not a constant expression}}
+ static const int overflow_shift3 = 1<<-1; // cxx11-error {{in-class initializer for static data member is not a constant expression}}
+ static const int overflow_shift4 = 1<<-1; // cxx11-error {{in-class initializer for static data member is not a constant expression}}
+ static const int overflow_shift5 = -1<<1; // cxx11-error {{in-class initializer for static data member is not a constant expression}}
void m() {
sx = 0;
diff --git a/clang/test/SemaCXX/enum.cpp b/clang/test/SemaCXX/enum.cpp
index 739d35ec4a06b..9c398cc8da886 100644
--- a/clang/test/SemaCXX/enum.cpp
+++ b/clang/test/SemaCXX/enum.cpp
@@ -103,14 +103,14 @@ void PR8089() {
// This is accepted as a GNU extension. In C++98, there was no provision for
// expressions with UB to be non-constant.
enum { overflow = 123456 * 234567 };
-#if __cplusplus >= 201103L
-// expected-warning at -2 {{expression is not an integral constant expression; folding it to a constant is a GNU extension}}
-// expected-note at -3 {{value 28958703552 is outside the range of representable values of type 'int'}}
-#else
-// expected-error at -5 {{expression is not an integral constant expression}}
-// expected-note at -6 {{value 28958703552 is outside the range of representable values of type 'int'}}
-// expected-warning at -7 {{overflow in expression; result is -1'106'067'520 with type 'int'}}
+// expected-error at -1 {{expression is not an integral constant expression}}
+// expected-note at -2 {{value 28958703552 is outside the range of representable values of type 'int'}}
+#if __cplusplus < 201103L
+// expected-warning at -4 {{overflow in expression; result is -1'106'067'520 with type 'int'}}
#endif
+enum { overflow_shift = 1 << 32 };
+// expected-error at -1 {{expression is not an integral constant expression}}
+// expected-note at -2 {{shift count 32 >= width of type 'int' (32 bits)}}
// FIXME: This is not consistent with the above case.
enum NoFold : int { overflow2 = 123456 * 234567 };
@@ -123,6 +123,16 @@ enum NoFold : int { overflow2 = 123456 * 234567 };
// expected-error at -7 {{expression is not an integral constant expression}}
// expected-note at -8 {{value 28958703552 is outside the range of representable values of type 'int'}}
#endif
+enum : int { overflow2_shift = 1 << 32 };
+#if __cplusplus >= 201103L
+// expected-error at -2 {{enumerator value is not a constant expression}}
+// expected-note at -3 {{shift count 32 >= width of type 'int' (32 bits)}}
+#else
+// expected-error at -5 {{expression is not an integral constant expression}}
+// expected-note at -6 {{shift count 32 >= width of type 'int' (32 bits)}}
+// expected-warning at -7 {{enumeration types with a fixed underlying type are a C++11 extension}}
+#endif
+
// PR28903
struct PR28903 {
``````````
</details>
https://github.com/llvm/llvm-project/pull/100452
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