Index: lib/Basic/Targets/RISCV.h
===================================================================
--- lib/Basic/Targets/RISCV.h
+++ lib/Basic/Targets/RISCV.h
@@ -88,6 +88,11 @@
     }
     return false;
   }
+
+  void setMaxAtomicWidth() override {
+    if (HasA)
+      MaxAtomicPromoteWidth = MaxAtomicInlineWidth = 32;
+  }
 };
 class LLVM_LIBRARY_VISIBILITY RISCV64TargetInfo : public RISCVTargetInfo {
 public:
@@ -106,6 +111,11 @@
     }
     return false;
   }
+
+  void setMaxAtomicWidth() override {
+    if (HasA)
+      MaxAtomicPromoteWidth = MaxAtomicInlineWidth = 64;
+  }
 };
 } // namespace targets
 } // namespace clang
Index: test/CodeGen/riscv-atomics.c
===================================================================
--- /dev/null
+++ test/CodeGen/riscv-atomics.c
@@ -0,0 +1,68 @@
+// RUN: %clang_cc1 -triple riscv32 -O1 -emit-llvm %s -o - \
+// RUN:   | FileCheck %s -check-prefix=RV32I
+// RUN: %clang_cc1 -triple riscv32 -target-feature +a -O1 -emit-llvm %s -o - \
+// RUN:   | FileCheck %s -check-prefix=RV32IA
+// RUN: %clang_cc1 -triple riscv64 -O1 -emit-llvm %s -o - \
+// RUN:   | FileCheck %s -check-prefix=RV64I
+// RUN: %clang_cc1 -triple riscv64 -target-feature +a -O1 -emit-llvm %s -o - \
+// RUN:   | FileCheck %s -check-prefix=RV64IA
+
+// This test demonstrates that MaxAtomicInlineWidth is set appropriately when
+// the atomics instruction set extension is enabled.
+
+#include <stdatomic.h>
+#include <stdint.h>
+
+void test_i8_atomics(_Atomic(int8_t) * a, int8_t b) {
+  // RV32I:  call zeroext i8 @__atomic_load_1
+  // RV32I:  call void @__atomic_store_1
+  // RV32I:  call zeroext i8 @__atomic_fetch_add_1
+  // RV32IA: load atomic i8, i8* %a seq_cst, align 1
+  // RV32IA: store atomic i8 %b, i8* %a seq_cst, align 1
+  // RV32IA: atomicrmw add i8* %a, i8 %b seq_cst
+  // RV64I:  call zeroext i8 @__atomic_load_1
+  // RV64I:  call void @__atomic_store_1
+  // RV64I:  call zeroext i8 @__atomic_fetch_add_1
+  // RV64IA: load atomic i8, i8* %a seq_cst, align 1
+  // RV64IA: store atomic i8 %b, i8* %a seq_cst, align 1
+  // RV64IA: atomicrmw add i8* %a, i8 %b seq_cst
+  __c11_atomic_load(a, memory_order_seq_cst);
+  __c11_atomic_store(a, b, memory_order_seq_cst);
+  __c11_atomic_fetch_add(a, b, memory_order_seq_cst);
+}
+
+void test_i32_atomics(_Atomic(int32_t) * a, int32_t b) {
+  // RV32I:  call i32 @__atomic_load_4
+  // RV32I:  call void @__atomic_store_4
+  // RV32I:  call i32 @__atomic_fetch_add_4
+  // RV32IA: load atomic i32, i32* %a seq_cst, align 4
+  // RV32IA: store atomic i32 %b, i32* %a seq_cst, align 4
+  // RV32IA: atomicrmw add i32* %a, i32 %b seq_cst
+  // RV64I:  call signext i32 @__atomic_load_4
+  // RV64I:  call void @__atomic_store_4
+  // RV64I:  call signext i32 @__atomic_fetch_add_4
+  // RV64IA: load atomic i32, i32* %a seq_cst, align 4
+  // RV64IA: store atomic i32 %b, i32* %a seq_cst, align 4
+  // RV64IA: atomicrmw add i32* %a, i32 %b seq_cst
+  __c11_atomic_load(a, memory_order_seq_cst);
+  __c11_atomic_store(a, b, memory_order_seq_cst);
+  __c11_atomic_fetch_add(a, b, memory_order_seq_cst);
+}
+
+void test_i64_atomics(_Atomic(int64_t) * a, int64_t b) {
+  // RV32I:  call i64 @__atomic_load_8
+  // RV32I:  call void @__atomic_store_8
+  // RV32I:  call i64 @__atomic_fetch_add_8
+  // RV32IA: call i64 @__atomic_load_8
+  // RV32IA: call void @__atomic_store_8
+  // RV32IA: call i64 @__atomic_fetch_add_8
+  // RV64I:  call i64 @__atomic_load_8
+  // RV64I:  call void @__atomic_store_8
+  // RV64I:  call i64 @__atomic_fetch_add_8
+  // RV64IA: load atomic i64, i64* %a seq_cst, align 8
+  // RV64IA: store atomic i64 %b, i64* %a seq_cst, align 8
+  // RV64IA: atomicrmw add i64* %a, i64 %b seq_cst
+  __c11_atomic_load(a, memory_order_seq_cst);
+  __c11_atomic_store(a, b, memory_order_seq_cst);
+  __c11_atomic_fetch_add(a, b, memory_order_seq_cst);
+}