[CodeGen] Emit Constants for immediate inlineasm arguments.

For inline assembly immediate constraints, we currently always use
EmitScalarExpr, instead of directly emitting the constant. When the
overflow sanitizer is enabled, this generates overflow intrinsics
instead of constants.

Instead, emit a constant for constraints that either require an
immediate (e.g. 'I' on X86), or only accepts constants (immediate
or symbolic; i.e., don't accept registers or memory).

Fixes PR19763.

Differential Revision: http://reviews.llvm.org/D10255

llvm-svn: 239549

clang/lib/CodeGen/CGStmt.cpp

@@ -1750,6 +1750,16 @@ llvm::Value* CodeGenFunction::EmitAsmInput(
                                          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);

clang/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));
+}