[clang] [compiler-rt] [clang][UBSan] Add implicit conversion check for bitfields (PR #75481)

[John McCall via llvm-commits]

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@@ -5570,11 +5570,44 @@ LValue CodeGenFunction::EmitBinaryOperatorLValue(const BinaryOperator *E) {
       break;
     }
 
-    RValue RV = EmitAnyExpr(E->getRHS());
+    llvm::Value *Previous = nullptr;
+    RValue RV;
+    QualType SrcType = E->getRHS()->getType();
+    // If LHS refers to a bitfield we want to retrieve the value before
+    // implicit conversion between the bitfield type and the RHS type
+    // and evaluate RHS without integer sanitizer checks (if passed)
+    if (auto *ICE = RetrieveImplicitCastExprForBitfieldSanitizer(E)) {
+      SrcType = ICE->getSubExpr()->getType();
+      Previous = EmitScalarExpr(ICE->getSubExpr());
+      // Pass default ScalarConversionOpts so that sanitizer check is
+      // not emitted here
+      llvm::Value *RHS = EmitScalarConversion(Previous, SrcType, ICE->getType(),
+                                              ICE->getExprLoc());
+      RV = RValue::get(RHS);
+    }
+
+    if (!Previous)
+      RV = EmitAnyExpr(E->getRHS());
+
     LValue LV = EmitCheckedLValue(E->getLHS(), TCK_Store);
+
     if (RV.isScalar())
       EmitNullabilityCheck(LV, RV.getScalarVal(), E->getExprLoc());
-    EmitStoreThroughLValue(RV, LV);
+
+    // Passing a pointer EmitStoreThroughBitfieldLValue will emit the result
+    // If sanitizer checks are not used, we do not use the result
+    // Hence, use EmitStoreThroughLValue instead
+    if (SanOpts.hasOneOf(SanitizerKind::ImplicitBitfieldConversion) &&
+        LV.isBitField() && RV.isScalar()) {
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rjmccall wrote:

Integer types always use scalar emission.

https://github.com/llvm/llvm-project/pull/75481