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[CIR] Fix for missing side effects during null pointer initialization #1547

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Merged
merged 1 commit into from
Apr 4, 2025
Merged

[CIR] Fix for missing side effects during null pointer initialization #1547

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10 changes: 7 additions & 3 deletions clang/lib/CIR/CodeGen/CIRGenExprScalar.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1180,9 +1180,11 @@ mlir::Value CIRGenFunction::emitPromotedScalarExpr(const Expr *E,
}

[[maybe_unused]] static bool MustVisitNullValue(const Expr *E) {
// If a null pointer expression's type is the C++0x nullptr_t, then
// it's not necessarily a simple constant and it must be evaluated
// If a null pointer expression's type is the C++0x nullptr_t and
// the expression is not a simple literal, it must be evaluated
// for its potential side effects.
if (isa<IntegerLiteral>(E) || isa<CXXNullPtrLiteralExpr>(E))
return false;
return E->getType()->isNullPtrType();
}

Expand Down Expand Up @@ -1723,7 +1725,9 @@ mlir::Value ScalarExprEmitter::VisitCastExpr(CastExpr *CE) {
return emitLValue(E).getPointer();

case CK_NullToPointer: {
// FIXME: use MustVisitNullValue(E) and evaluate expr.
if (MustVisitNullValue(E))
CGF.emitIgnoredExpr(E);

// Note that DestTy is used as the MLIR type instead of a custom
// nullptr type.
mlir::Type Ty = CGF.convertType(DestTy);
Expand Down
76 changes: 76 additions & 0 deletions clang/test/CIR/CodeGen/nullptr-init.cpp
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@@ -0,0 +1,76 @@
// RUN: %clang_cc1 -std=c++17 -triple x86_64-unknown-linux-gnu %s -fclangir -emit-cir -o %t.cir
// RUN: FileCheck --input-file=%t.cir -check-prefix=CIR %s
// RUN: %clang_cc1 -std=c++17 -triple x86_64-unknown-linux-gnu %s -fclangir -emit-llvm -o %t.ll
// RUN: FileCheck --input-file=%t.ll -check-prefix=LLVM %s

void t1() {
int *p1 = nullptr;
int *p2 = 0;
int *p3 = (int*)0;
}

// CIR: cir.func @_Z2t1v()
// CIR-NEXT: %[[P1:.*]] = cir.alloca !cir.ptr<!s32i>, !cir.ptr<!cir.ptr<!s32i>>, ["p1", init] {alignment = 8 : i64}
// CIR-NEXT: %[[P2:.*]] = cir.alloca !cir.ptr<!s32i>, !cir.ptr<!cir.ptr<!s32i>>, ["p2", init] {alignment = 8 : i64}
// CIR-NEXT: %[[P3:.*]] = cir.alloca !cir.ptr<!s32i>, !cir.ptr<!cir.ptr<!s32i>>, ["p3", init] {alignment = 8 : i64}
// CIR-NEXT: %[[NULLPTR1:.*]] = cir.const #cir.ptr<null> : !cir.ptr<!s32i>
// CIR-NEXT: cir.store %[[NULLPTR1]], %[[P1]] : !cir.ptr<!s32i>, !cir.ptr<!cir.ptr<!s32i>>
// CIR-NEXT: %[[NULLPTR2:.*]] = cir.const #cir.ptr<null> : !cir.ptr<!s32i>
// CIR-NEXT: cir.store %[[NULLPTR2]], %[[P2]] : !cir.ptr<!s32i>, !cir.ptr<!cir.ptr<!s32i>>
// CIR-NEXT: %[[NULLPTR3:.*]] = cir.const #cir.ptr<null> : !cir.ptr<!s32i>
// CIR-NEXT: cir.store %[[NULLPTR3]], %[[P3]] : !cir.ptr<!s32i>, !cir.ptr<!cir.ptr<!s32i>>
// CIR-NEXT: cir.return
// CIR-NEXT: }

// LLVM: define{{.*}} @_Z2t1v()
// LLVM-NEXT: %[[P1:.*]] = alloca ptr, i64 1, align 8
// LLVM-NEXT: %[[P2:.*]] = alloca ptr, i64 1, align 8
// LLVM-NEXT: %[[P3:.*]] = alloca ptr, i64 1, align 8
// LLVM-NEXT: store ptr null, ptr %[[P1]], align 8
// LLVM-NEXT: store ptr null, ptr %[[P2]], align 8
// LLVM-NEXT: store ptr null, ptr %[[P3]], align 8
// LLVM-NEXT: ret void
// LLVM-NEXT: }

// Verify that we're capturing side effects during null pointer initialization.
int t2() {
int x = 0;
int *p = (x = 1, nullptr);
return x;
}

// Note: An extra null pointer constant gets emitted as a result of visiting the
// compound initialization expression. We could avoid this by capturing
// the result of the compound initialization expression and explicitly
// casting it to the required type, but a redundant constant seems less
// intrusive than a redundant bitcast.

// CIR: cir.func @_Z2t2v()
// CIR-NEXT: %[[RETVAL_ADDR:.*]] = cir.alloca !s32i, !cir.ptr<!s32i>, ["__retval"] {alignment = 4 : i64}
// CIR-NEXT: %[[X:.*]] = cir.alloca !s32i, !cir.ptr<!s32i>, ["x", init] {alignment = 4 : i64}
// CIR-NEXT: %[[P:.*]] = cir.alloca !cir.ptr<!s32i>, !cir.ptr<!cir.ptr<!s32i>>, ["p", init] {alignment = 8 : i64}
// CIR-NEXT: %[[ZERO:.*]] = cir.const #cir.int<0> : !s32i
// CIR-NEXT: cir.store %[[ZERO]], %[[X]] : !s32i, !cir.ptr<!s32i>
// CIR-NEXT: %[[ONE:.*]] = cir.const #cir.int<1> : !s32i
// CIR-NEXT: cir.store %[[ONE]], %[[X]] : !s32i, !cir.ptr<!s32i>
// CIR-NEXT: %[[NULLPTR_EXTRA:.*]] = cir.const #cir.ptr<null> : !cir.ptr<!void>
// CIR-NEXT: %[[NULLPTR:.*]] = cir.const #cir.ptr<null> : !cir.ptr<!s32i>
// CIR-NEXT: cir.store %[[NULLPTR]], %[[P]] : !cir.ptr<!s32i>, !cir.ptr<!cir.ptr<!s32i>>
// CIR-NEXT: %[[X_VAL:.*]] = cir.load %[[X]] : !cir.ptr<!s32i>, !s32i
// CIR-NEXT: cir.store %[[X_VAL]], %[[RETVAL_ADDR]] : !s32i, !cir.ptr<!s32i>
// CIR-NEXT: %[[RETVAL:.*]] = cir.load %[[RETVAL_ADDR]] : !cir.ptr<!s32i>, !s32i
// CIR-NEXT: cir.return %[[RETVAL]] : !s32i
// CIR-NEXT: }

// LLVM: define{{.*}} @_Z2t2v()
// LLVM-NEXT: %[[RETVAL_ADDR:.*]] = alloca i32, i64 1, align 4
// LLVM-NEXT: %[[X:.*]] = alloca i32, i64 1, align 4
// LLVM-NEXT: %[[P:.*]] = alloca ptr, i64 1, align 8
// LLVM-NEXT: store i32 0, ptr %[[X]], align 4
// LLVM-NEXT: store i32 1, ptr %[[X]], align 4
// LLVM-NEXT: store ptr null, ptr %[[P]], align 8
// LLVM-NEXT: %[[X_VAL:.*]] = load i32, ptr %[[X]], align 4
// LLVM-NEXT: store i32 %[[X_VAL]], ptr %[[RETVAL_ADDR]], align 4
// LLVM-NEXT: %[[RETVAL:.*]] = load i32, ptr %[[RETVAL_ADDR]], align 4
// LLVM-NEXT: ret i32 %[[RETVAL]]
// LLVM-NEXT: }
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