xgupta created this revision.
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This fixes https://github.com/llvm/llvm-project/issues/52873.
Don't warn in C++2A mode (and newer), as signed left shifts
always wrap and never overflow. Ref. -
https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p1236r1.html.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D127518
Files:
clang/lib/Sema/SemaExpr.cpp
clang/test/CXX/expr/expr.const/p2-0x.cpp
clang/test/SemaCXX/constant-expression-cxx2a.cpp
clang/test/SemaCXX/shift.cpp
Index: clang/test/SemaCXX/shift.cpp
===================================================================
--- clang/test/SemaCXX/shift.cpp
+++ clang/test/SemaCXX/shift.cpp
@@ -41,7 +41,7 @@
int i;
i = 1 << (WORD_BIT - 2);
- i = 2 << (WORD_BIT - 1); // expected-warning {{bits to represent, but 'int'
only has}}
+ i = 2 << (WORD_BIT - 1); // cxx17-warning {{bits to represent, but 'int'
only has}}
i = 1 << (WORD_BIT - 1); // expected-warning {{sets the sign bit of the
shift expression}}
i = -1 << (WORD_BIT - 1); // cxx17-warning {{shifting a negative signed
value is undefined}}
i = -1 << 0; // cxx17-warning {{shifting a negative signed value is
undefined}}
@@ -53,7 +53,7 @@
u = 5U << (WORD_BIT - 1);
long long int lli;
- lli = INT_MIN << 2; // cxx17-warning {{shifting a negative signed value is
undefined}} cxx2a-warning {{requires 34 bits to represent}}
+ lli = INT_MIN << 2; // cxx17-warning {{shifting a negative signed value is
undefined}}
lli = 1LL << (sizeof(long long) * CHAR_BIT - 2);
}
Index: clang/test/SemaCXX/constant-expression-cxx2a.cpp
===================================================================
--- clang/test/SemaCXX/constant-expression-cxx2a.cpp
+++ clang/test/SemaCXX/constant-expression-cxx2a.cpp
@@ -530,8 +530,8 @@
using int32 = __INT32_TYPE__;
static_assert(uint32(int32(0x1234) << 16) == 0x12340000);
static_assert(uint32(int32(0x1234) << 19) == 0x91a00000);
- static_assert(uint32(int32(0x1234) << 20) == 0x23400000); //
expected-warning {{requires 34 bits}}
- static_assert(uint32(int32(0x1234) << 24) == 0x34000000); //
expected-warning {{requires 38 bits}}
+ static_assert(uint32(int32(0x1234) << 20) == 0x23400000);
+ static_assert(uint32(int32(0x1234) << 24) == 0x34000000);
static_assert(uint32(int32(-1) << 31) == 0x80000000);
static_assert(-1 >> 1 == -1);
Index: clang/test/CXX/expr/expr.const/p2-0x.cpp
===================================================================
--- clang/test/CXX/expr/expr.const/p2-0x.cpp
+++ clang/test/CXX/expr/expr.const/p2-0x.cpp
@@ -162,9 +162,9 @@
constexpr int shl_signed_ok = 1 << 30; // ok
constexpr int shl_signed_into_sign = 1 << 31; // ok (DR1457)
constexpr int shl_signed_into_sign_2 = 0x7fffffff << 1; // ok (DR1457)
- constexpr int shl_signed_off_end = 2 << 31; // cxx11-error {{constant
expression}} cxx11-note {{signed left shift discards bits}} expected-warning
{{signed shift result (0x100000000) requires 34 bits to represent, but 'int'
only has 32 bits}}
- constexpr int shl_signed_off_end_2 = 0x7fffffff << 2; // cxx11-error
{{constant expression}} cxx11-note {{signed left shift discards bits}}
expected-warning {{signed shift result (0x1FFFFFFFC) requires 34 bits to
represent, but 'int' only has 32 bits}}
- constexpr int shl_signed_overflow = 1024 << 31; // cxx11-error {{constant
expression}} cxx11-note {{signed left shift discards bits}} expected-warning
{{requires 43 bits to represent}}
+ constexpr int shl_signed_off_end = 2 << 31; // cxx11-error {{constant
expression}} cxx11-note {{signed left shift discards bits}} cxx11-warning
{{signed shift result (0x100000000) requires 34 bits to represent, but 'int'
only has 32 bits}}
+ constexpr int shl_signed_off_end_2 = 0x7fffffff << 2; // cxx11-error
{{constant expression}} cxx11-note {{signed left shift discards bits}}
cxx11-warning {{signed shift result (0x1FFFFFFFC) requires 34 bits to
represent, but 'int' only has 32 bits}}
+ constexpr int shl_signed_overflow = 1024 << 31; // cxx11-error {{constant
expression}} cxx11-note {{signed left shift discards bits}} cxx11-warning
{{requires 43 bits to represent}}
constexpr int shl_signed_ok2 = 1024 << 20; // ok
constexpr int shr_m1 = 0 >> -1; // expected-error {{constant expression}}
expected-note {{negative shift count -1}}
Index: clang/lib/Sema/SemaExpr.cpp
===================================================================
--- clang/lib/Sema/SemaExpr.cpp
+++ clang/lib/Sema/SemaExpr.cpp
@@ -11453,6 +11453,9 @@
return;
}
+ if (S.getLangOpts().CPlusPlus20)
+ return;
+
S.Diag(Loc, diag::warn_shift_result_gt_typewidth)
<< HexResult.str() << Result.getMinSignedBits() << LHSType
<< Left.getBitWidth() << LHS.get()->getSourceRange()
Index: clang/test/SemaCXX/shift.cpp
===================================================================
--- clang/test/SemaCXX/shift.cpp
+++ clang/test/SemaCXX/shift.cpp
@@ -41,7 +41,7 @@
int i;
i = 1 << (WORD_BIT - 2);
- i = 2 << (WORD_BIT - 1); // expected-warning {{bits to represent, but 'int' only has}}
+ i = 2 << (WORD_BIT - 1); // cxx17-warning {{bits to represent, but 'int' only has}}
i = 1 << (WORD_BIT - 1); // expected-warning {{sets the sign bit of the shift expression}}
i = -1 << (WORD_BIT - 1); // cxx17-warning {{shifting a negative signed value is undefined}}
i = -1 << 0; // cxx17-warning {{shifting a negative signed value is undefined}}
@@ -53,7 +53,7 @@
u = 5U << (WORD_BIT - 1);
long long int lli;
- lli = INT_MIN << 2; // cxx17-warning {{shifting a negative signed value is undefined}} cxx2a-warning {{requires 34 bits to represent}}
+ lli = INT_MIN << 2; // cxx17-warning {{shifting a negative signed value is undefined}}
lli = 1LL << (sizeof(long long) * CHAR_BIT - 2);
}
Index: clang/test/SemaCXX/constant-expression-cxx2a.cpp
===================================================================
--- clang/test/SemaCXX/constant-expression-cxx2a.cpp
+++ clang/test/SemaCXX/constant-expression-cxx2a.cpp
@@ -530,8 +530,8 @@
using int32 = __INT32_TYPE__;
static_assert(uint32(int32(0x1234) << 16) == 0x12340000);
static_assert(uint32(int32(0x1234) << 19) == 0x91a00000);
- static_assert(uint32(int32(0x1234) << 20) == 0x23400000); // expected-warning {{requires 34 bits}}
- static_assert(uint32(int32(0x1234) << 24) == 0x34000000); // expected-warning {{requires 38 bits}}
+ static_assert(uint32(int32(0x1234) << 20) == 0x23400000);
+ static_assert(uint32(int32(0x1234) << 24) == 0x34000000);
static_assert(uint32(int32(-1) << 31) == 0x80000000);
static_assert(-1 >> 1 == -1);
Index: clang/test/CXX/expr/expr.const/p2-0x.cpp
===================================================================
--- clang/test/CXX/expr/expr.const/p2-0x.cpp
+++ clang/test/CXX/expr/expr.const/p2-0x.cpp
@@ -162,9 +162,9 @@
constexpr int shl_signed_ok = 1 << 30; // ok
constexpr int shl_signed_into_sign = 1 << 31; // ok (DR1457)
constexpr int shl_signed_into_sign_2 = 0x7fffffff << 1; // ok (DR1457)
- constexpr int shl_signed_off_end = 2 << 31; // cxx11-error {{constant expression}} cxx11-note {{signed left shift discards bits}} expected-warning {{signed shift result (0x100000000) requires 34 bits to represent, but 'int' only has 32 bits}}
- constexpr int shl_signed_off_end_2 = 0x7fffffff << 2; // cxx11-error {{constant expression}} cxx11-note {{signed left shift discards bits}} expected-warning {{signed shift result (0x1FFFFFFFC) requires 34 bits to represent, but 'int' only has 32 bits}}
- constexpr int shl_signed_overflow = 1024 << 31; // cxx11-error {{constant expression}} cxx11-note {{signed left shift discards bits}} expected-warning {{requires 43 bits to represent}}
+ constexpr int shl_signed_off_end = 2 << 31; // cxx11-error {{constant expression}} cxx11-note {{signed left shift discards bits}} cxx11-warning {{signed shift result (0x100000000) requires 34 bits to represent, but 'int' only has 32 bits}}
+ constexpr int shl_signed_off_end_2 = 0x7fffffff << 2; // cxx11-error {{constant expression}} cxx11-note {{signed left shift discards bits}} cxx11-warning {{signed shift result (0x1FFFFFFFC) requires 34 bits to represent, but 'int' only has 32 bits}}
+ constexpr int shl_signed_overflow = 1024 << 31; // cxx11-error {{constant expression}} cxx11-note {{signed left shift discards bits}} cxx11-warning {{requires 43 bits to represent}}
constexpr int shl_signed_ok2 = 1024 << 20; // ok
constexpr int shr_m1 = 0 >> -1; // expected-error {{constant expression}} expected-note {{negative shift count -1}}
Index: clang/lib/Sema/SemaExpr.cpp
===================================================================
--- clang/lib/Sema/SemaExpr.cpp
+++ clang/lib/Sema/SemaExpr.cpp
@@ -11453,6 +11453,9 @@
return;
}
+ if (S.getLangOpts().CPlusPlus20)
+ return;
+
S.Diag(Loc, diag::warn_shift_result_gt_typewidth)
<< HexResult.str() << Result.getMinSignedBits() << LHSType
<< Left.getBitWidth() << LHS.get()->getSourceRange()
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