Index: llvm/lib/Target/RISCV/RISCVTargetMachine.cpp
===================================================================
--- llvm/lib/Target/RISCV/RISCVTargetMachine.cpp
+++ llvm/lib/Target/RISCV/RISCVTargetMachine.cpp
@@ -210,9 +210,13 @@
     addPass(createBarrierNoopPass());
   }
 
-  if (EnableGlobalMerge == cl::BOU_TRUE) {
-    addPass(createGlobalMergePass(TM, /* MaxOffset */ 2047,
-                                  /* OnlyOptimizeForSize */ false,
+  if ((TM->getOptLevel() != CodeGenOpt::None &&
+       EnableGlobalMerge == cl::BOU_UNSET) ||
+      EnableGlobalMerge == cl::BOU_TRUE) {
+    bool OnlyOptimizeForSize = (TM->getOptLevel() < CodeGenOpt::Aggressive) &&
+                               (EnableGlobalMerge == cl::BOU_UNSET);
+
+    addPass(createGlobalMergePass(TM, /* MaxOffset */ 2047, OnlyOptimizeForSize,
                                   /* MergeExternalByDefault */ true));
   }
 
Index: llvm/test/CodeGen/RISCV/O3-pipeline.ll
===================================================================
--- llvm/test/CodeGen/RISCV/O3-pipeline.ll
+++ llvm/test/CodeGen/RISCV/O3-pipeline.ll
@@ -63,6 +63,7 @@
 ; CHECK-NEXT:       Exception handling preparation
 ; CHECK-NEXT:     A No-Op Barrier Pass
 ; CHECK-NEXT:     FunctionPass Manager
+; CHECK-NEXT:       Merge internal globals
 ; CHECK-NEXT:       Safe Stack instrumentation pass
 ; CHECK-NEXT:       Insert stack protectors
 ; CHECK-NEXT:       Module Verifier
Index: llvm/test/CodeGen/RISCV/global-merge-minsize.ll
===================================================================
--- /dev/null
+++ llvm/test/CodeGen/RISCV/global-merge-minsize.ll
@@ -0,0 +1,43 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -mtriple=riscv32 -verify-machineinstrs < %s \
+; RUN:   | FileCheck %s
+; RUN: llc -mtriple=riscv64 -verify-machineinstrs < %s \
+; RUN:   | FileCheck %s
+
+@eg1 = dso_local global i32 0, align 4
+@eg2 = dso_local global i32 0, align 4
+@eg3 = dso_local global i32 0, align 4
+@eg4 = dso_local global i32 0, align 4
+
+; Demonstrate that at the default optimisation level, global merging takes
+; place for globals referenced in minsize functions but not others.
+
+define void @f1(i32 %a) nounwind {
+; CHECK-LABEL: f1:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    lui a1, %hi(eg1)
+; CHECK-NEXT:    sw a0, %lo(eg1)(a1)
+; CHECK-NEXT:    lui a1, %hi(eg2)
+; CHECK-NEXT:    sw a0, %lo(eg2)(a1)
+; CHECK-NEXT:    ret
+  store i32 %a, ptr @eg1, align 4
+  store i32 %a, ptr @eg2, align 4
+  ret void
+}
+
+; TODO: It would be better for code size to alter the first store below by
+; first fully materialising .L_MergedGlobals in a1 and then storing to it with
+; a 0 offset.
+
+define void @f2(i32 %a) nounwind minsize optsize {
+; CHECK-LABEL: f2:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    lui a1, %hi(.L_MergedGlobals)
+; CHECK-NEXT:    sw a0, %lo(.L_MergedGlobals)(a1)
+; CHECK-NEXT:    addi a1, a1, %lo(.L_MergedGlobals)
+; CHECK-NEXT:    sw a0, 4(a1)
+; CHECK-NEXT:    ret
+  store i32 %a, ptr @eg3, align 4
+  store i32 %a, ptr @eg4, align 4
+  ret void
+}