Index: lib/CodeGen/CGStmt.cpp
===================================================================
--- lib/CodeGen/CGStmt.cpp
+++ lib/CodeGen/CGStmt.cpp
@@ -1750,6 +1750,16 @@
                                          const TargetInfo::ConstraintInfo &Info,
                                            const Expr *InputExpr,
                                            std::string &ConstraintStr) {
+  // If this can't be a register or memory, i.e., has to be a constant
+  // (immediate or symbolic), try to emit it as such.
+  if (!Info.allowsRegister() && !Info.allowsMemory()) {
+    llvm::APSInt Result;
+    if (InputExpr->isIntegerConstantExpr(Result, getContext()))
+      return llvm::ConstantInt::get(getLLVMContext(), Result);
+    assert(!Info.requiresImmediateConstant() &&
+           "Required-immediate inlineasm arg isn't constant?");
+  }
+
   if (Info.allowsRegister() || !Info.allowsMemory())
     if (CodeGenFunction::hasScalarEvaluationKind(InputExpr->getType()))
       return EmitScalarExpr(InputExpr);
Index: test/CodeGen/inline-asm-immediate-ubsan.c
===================================================================
--- test/CodeGen/inline-asm-immediate-ubsan.c
+++ test/CodeGen/inline-asm-immediate-ubsan.c
@@ -0,0 +1,25 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown -emit-llvm -o - %s \
+// RUN:     -fsanitize=signed-integer-overflow \
+// RUN:   | FileCheck %s --check-prefix=CHECK
+
+// Verify we emit constants for "immediate" inline assembly arguments.
+// Emitting a scalar expression can make the immediate be generated as
+// overflow intrinsics, if the overflow sanitizer is enabled.
+
+// Check both 'i' and 'I':
+// - 'i' accepts symbolic constants.
+// - 'I' doesn't, and is really an immediate-required constraint.
+
+// See also PR23517.
+
+// CHECK-LABEL: @test_inlineasm_i
+// CHECK: call void asm sideeffect "int $0", "i{{.*}}"(i32 2)
+void test_inlineasm_i() {
+  __asm__ __volatile__("int %0" :: "i"(1 + 1));
+}
+
+// CHECK-LABEL: @test_inlineasm_I
+// CHECK: call void asm sideeffect "int $0", "I{{.*}}"(i32 2)
+void test_inlineasm_I() {
+  __asm__ __volatile__("int %0" :: "I"(1 + 1));
+}