diff --git a/llvm/include/llvm/CodeGen/GlobalISel/CombinerHelper.h b/llvm/include/llvm/CodeGen/GlobalISel/CombinerHelper.h
--- a/llvm/include/llvm/CodeGen/GlobalISel/CombinerHelper.h
+++ b/llvm/include/llvm/CodeGen/GlobalISel/CombinerHelper.h
@@ -228,6 +228,9 @@
   /// Optimize (cond ? x : x) -> x
   bool matchSelectSameVal(MachineInstr &MI);
 
+  /// Optimize (x op x) -> x
+  bool matchBinOpSameVal(MachineInstr &MI);
+
   /// Try to transform \p MI by using all of the above
   /// combine functions. Returns true if changed.
   bool tryCombine(MachineInstr &MI);
diff --git a/llvm/include/llvm/Target/GlobalISel/Combine.td b/llvm/include/llvm/Target/GlobalISel/Combine.td
--- a/llvm/include/llvm/Target/GlobalISel/Combine.td
+++ b/llvm/include/llvm/Target/GlobalISel/Combine.td
@@ -200,6 +200,14 @@
   (apply [{ return Helper.replaceSingleDefInstWithOperand(*${root}, 1); }])
 >;
 
+// Fold (x op x) - > x
+def binop_same_val: GICombineRule<
+  (defs root:$root),
+  (match (wip_match_opcode G_AND, G_OR):$root,
+    [{ return Helper.matchBinOpSameVal(*${root}); }]),
+  (apply [{ return Helper.replaceSingleDefInstWithOperand(*${root}, 1); }])
+>;
+
 // FIXME: These should use the custom predicate feature once it lands.
 def undef_combines : GICombineGroup<[undef_to_fp_zero, undef_to_int_zero,
                                      undef_to_negative_one,
@@ -207,7 +215,8 @@
                                      propagate_undef_all_ops,
                                      propagate_undef_shuffle_mask]>;
 
-def identity_combines : GICombineGroup<[select_same_val, right_identity_zero]>;
+def identity_combines : GICombineGroup<[select_same_val, right_identity_zero,
+                                        binop_same_val]>;
 
 def trivial_combines : GICombineGroup<[copy_prop, mul_to_shl]>;
 def all_combines : GICombineGroup<[trivial_combines, ptr_add_immed_chain,
diff --git a/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
--- a/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
@@ -1574,6 +1574,12 @@
                        MRI);
 }
 
+bool CombinerHelper::matchBinOpSameVal(MachineInstr &MI) {
+  return matchEqualDefs(MI.getOperand(1), MI.getOperand(2)) &&
+         canReplaceReg(MI.getOperand(0).getReg(), MI.getOperand(1).getReg(),
+                       MRI);
+}
+
 bool CombinerHelper::replaceInstWithFConstant(MachineInstr &MI, double C) {
   assert(MI.getNumDefs() == 1 && "Expected only one def?");
   Builder.setInstr(MI);
diff --git a/llvm/test/CodeGen/AArch64/GlobalISel/arm64-fallback.ll b/llvm/test/CodeGen/AArch64/GlobalISel/arm64-fallback.ll
--- a/llvm/test/CodeGen/AArch64/GlobalISel/arm64-fallback.ll
+++ b/llvm/test/CodeGen/AArch64/GlobalISel/arm64-fallback.ll
@@ -153,7 +153,9 @@
 define void @nonpow2_or_narrowing() {
   %a = add i128 undef, undef
   %b = trunc i128 %a to i96
-  %dummy = or i96 %b, %b
+  %a2 = add i128 undef, undef
+  %b2 = trunc i128 %a2 to i96
+  %dummy = or i96 %b, %b2
   store i96 %dummy, i96* undef
   ret void
 }
diff --git a/llvm/test/CodeGen/AArch64/GlobalISel/prelegalizercombiner-binop-same-val.mir b/llvm/test/CodeGen/AArch64/GlobalISel/prelegalizercombiner-binop-same-val.mir
new file mode 100644
--- /dev/null
+++ b/llvm/test/CodeGen/AArch64/GlobalISel/prelegalizercombiner-binop-same-val.mir
@@ -0,0 +1,96 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc -mtriple aarch64 -run-pass=aarch64-prelegalizer-combiner -verify-machineinstrs %s -o - | FileCheck %s
+
+name:            or_same
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    liveins: $x0
+
+    ; Fold: x or x -> x
+    ; CHECK-LABEL: name: or_same
+    ; CHECK: liveins: $x0
+    ; CHECK: %copy:_(s64) = COPY $x0
+    ; CHECK: $x0 = COPY %copy(s64)
+    ; CHECK: RET_ReallyLR implicit $x0
+    %copy:_(s64) = COPY $x0
+    %or:_(s64) = G_OR %copy, %copy
+    $x0 = COPY %or(s64)
+    RET_ReallyLR implicit $x0
+
+...
+---
+name:            and_same
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    liveins: $x0
+
+    ; Fold: x and x -> x
+
+    ; CHECK-LABEL: name: and_same
+    ; CHECK: liveins: $x0
+    ; CHECK: %copy:_(s64) = COPY $x0
+    ; CHECK: $x0 = COPY %copy(s64)
+    ; CHECK: RET_ReallyLR implicit $x0
+    %copy:_(s64) = COPY $x0
+    %and:_(s64) = G_AND %copy, %copy
+    $x0 = COPY %and(s64)
+    RET_ReallyLR implicit $x0
+
+...
+---
+name:            and_same2
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    liveins: $x0, $x1
+
+    ; We can fold when the LHS and RHS are guaranteed to be identical.
+
+    ; CHECK-LABEL: name: and_same2
+    ; CHECK: liveins: $x0, $x1
+    ; CHECK: %copy1:_(s64) = COPY $x0
+    ; CHECK: %copy2:_(s64) = COPY $x1
+    ; CHECK: %or:_(s64) = G_OR %copy1, %copy2
+    ; CHECK: $x0 = COPY %or(s64)
+    ; CHECK: RET_ReallyLR implicit $x0
+    %copy1:_(s64) = COPY $x0
+    %copy2:_(s64) = COPY $x1
+    %or:_(s64) = G_OR %copy1, %copy2
+    %same_as_or:_(s64) = COPY %or(s64)
+    %and:_(s64) = G_AND %or, %same_as_or
+    $x0 = COPY %and(s64)
+    RET_ReallyLR implicit $x0
+
+...
+---
+name:            or_and_not_same
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    liveins: $x0, $x1, $x2
+
+    ; None of the G_ORs or G_ANDs should be eliminated here, because their LHS
+    ; and RHS values are different.
+
+    ; CHECK-LABEL: name: or_and_not_same
+    ; CHECK: liveins: $x0, $x1, $x2
+    ; CHECK: %copy1:_(s64) = COPY $x0
+    ; CHECK: %copy2:_(s64) = COPY $x1
+    ; CHECK: %copy3:_(s64) = COPY $x2
+    ; CHECK: %or1:_(s64) = G_OR %copy1, %copy2
+    ; CHECK: %or2:_(s64) = G_OR %copy1, %copy3
+    ; CHECK: %and:_(s64) = G_AND %or1, %or2
+    ; CHECK: $x0 = COPY %and(s64)
+    ; CHECK: RET_ReallyLR implicit $x0
+    %copy1:_(s64) = COPY $x0
+    %copy2:_(s64) = COPY $x1
+    %copy3:_(s64) = COPY $x2
+    %or1:_(s64) = G_OR %copy1, %copy2
+    %or2:_(s64) = G_OR %copy1, %copy3
+    %and:_(s64) = G_AND %or1, %or2
+    $x0 = COPY %and(s64)
+    RET_ReallyLR implicit $x0
+
+...