diff --git a/llvm/lib/Target/AArch64/AArch64Combine.td b/llvm/lib/Target/AArch64/AArch64Combine.td
--- a/llvm/lib/Target/AArch64/AArch64Combine.td
+++ b/llvm/lib/Target/AArch64/AArch64Combine.td
@@ -203,6 +203,7 @@
                         extractvecelt_pairwise_add, redundant_or,
                         mul_const, redundant_sext_inreg,
                         form_bitfield_extract, rotate_out_of_range,
-                        icmp_to_true_false_known_bits, merge_unmerge]> {
+                        icmp_to_true_false_known_bits, merge_unmerge,
+                        select_combines]> {
   let DisableRuleOption = "aarch64postlegalizercombiner-disable-rule";
 }
diff --git a/llvm/test/CodeGen/AArch64/GlobalISel/arm64-atomic-128.ll b/llvm/test/CodeGen/AArch64/GlobalISel/arm64-atomic-128.ll
--- a/llvm/test/CodeGen/AArch64/GlobalISel/arm64-atomic-128.ll
+++ b/llvm/test/CodeGen/AArch64/GlobalISel/arm64-atomic-128.ll
@@ -351,27 +351,14 @@
 ; CHECK-LLSC-O1-NEXT:    sub x9, x8, #64 // =64
 ; CHECK-LLSC-O1-NEXT:  .LBB4_1: // %atomicrmw.start
 ; CHECK-LLSC-O1-NEXT:    // =>This Inner Loop Header: Depth=1
-; CHECK-LLSC-O1-NEXT:    ldxp x11, x10, [x2]
-; CHECK-LLSC-O1-NEXT:    sub x12, x8, #64 // =64
-; CHECK-LLSC-O1-NEXT:    tst wzr, #0x1
-; CHECK-LLSC-O1-NEXT:    lsl x13, x10, x8
-; CHECK-LLSC-O1-NEXT:    lsr x14, x10, x9
-; CHECK-LLSC-O1-NEXT:    lsl x10, x10, x12
-; CHECK-LLSC-O1-NEXT:    csel x10, x14, x10, ne
-; CHECK-LLSC-O1-NEXT:    csel x13, x13, xzr, ne
-; CHECK-LLSC-O1-NEXT:    csel x10, xzr, x10, ne
-; CHECK-LLSC-O1-NEXT:    orr x11, x11, x13
-; CHECK-LLSC-O1-NEXT:    lsl x13, x10, x9
-; CHECK-LLSC-O1-NEXT:    lsr x12, x10, x12
-; CHECK-LLSC-O1-NEXT:    orr x13, x13, x11, lsr #0
-; CHECK-LLSC-O1-NEXT:    tst wzr, #0x1
-; CHECK-LLSC-O1-NEXT:    csel x12, x13, x12, ne
-; CHECK-LLSC-O1-NEXT:    csel x12, x11, x12, ne
-; CHECK-LLSC-O1-NEXT:    stxp w13, x11, x12, [x2]
-; CHECK-LLSC-O1-NEXT:    cbnz w13, .LBB4_1
+; CHECK-LLSC-O1-NEXT:    ldxp x10, x8, [x2]
+; CHECK-LLSC-O1-NEXT:    lsl x8, x8, x9
+; CHECK-LLSC-O1-NEXT:    lsr x11, x8, x9
+; CHECK-LLSC-O1-NEXT:    stxp w12, x10, x11, [x2]
+; CHECK-LLSC-O1-NEXT:    cbnz w12, .LBB4_1
 ; CHECK-LLSC-O1-NEXT:  // %bb.2: // %atomicrmw.end
-; CHECK-LLSC-O1-NEXT:    mov v0.d[0], x11
-; CHECK-LLSC-O1-NEXT:    mov v0.d[1], x10
+; CHECK-LLSC-O1-NEXT:    mov v0.d[0], x10
+; CHECK-LLSC-O1-NEXT:    mov v0.d[1], x8
 ; CHECK-LLSC-O1-NEXT:    str q0, [x3]
 ; CHECK-LLSC-O1-NEXT:    ret
 ;
@@ -381,27 +368,14 @@
 ; CHECK-CAS-O1-NEXT:    sub x9, x8, #64 // =64
 ; CHECK-CAS-O1-NEXT:  .LBB4_1: // %atomicrmw.start
 ; CHECK-CAS-O1-NEXT:    // =>This Inner Loop Header: Depth=1
-; CHECK-CAS-O1-NEXT:    ldxp x11, x10, [x2]
-; CHECK-CAS-O1-NEXT:    sub x12, x8, #64 // =64
-; CHECK-CAS-O1-NEXT:    lsl x13, x10, x8
-; CHECK-CAS-O1-NEXT:    lsr x14, x10, x9
-; CHECK-CAS-O1-NEXT:    lsl x10, x10, x12
-; CHECK-CAS-O1-NEXT:    tst wzr, #0x1
-; CHECK-CAS-O1-NEXT:    csel x13, x13, xzr, ne
-; CHECK-CAS-O1-NEXT:    csel x10, x14, x10, ne
-; CHECK-CAS-O1-NEXT:    csel x10, xzr, x10, ne
-; CHECK-CAS-O1-NEXT:    orr x11, x11, x13
-; CHECK-CAS-O1-NEXT:    lsl x13, x10, x9
-; CHECK-CAS-O1-NEXT:    orr x13, x13, x11, lsr #0
-; CHECK-CAS-O1-NEXT:    lsr x12, x10, x12
-; CHECK-CAS-O1-NEXT:    tst wzr, #0x1
-; CHECK-CAS-O1-NEXT:    csel x12, x13, x12, ne
-; CHECK-CAS-O1-NEXT:    csel x12, x11, x12, ne
-; CHECK-CAS-O1-NEXT:    stxp w13, x11, x12, [x2]
-; CHECK-CAS-O1-NEXT:    cbnz w13, .LBB4_1
+; CHECK-CAS-O1-NEXT:    ldxp x10, x8, [x2]
+; CHECK-CAS-O1-NEXT:    lsl x8, x8, x9
+; CHECK-CAS-O1-NEXT:    lsr x11, x8, x9
+; CHECK-CAS-O1-NEXT:    stxp w12, x10, x11, [x2]
+; CHECK-CAS-O1-NEXT:    cbnz w12, .LBB4_1
 ; CHECK-CAS-O1-NEXT:  // %bb.2: // %atomicrmw.end
-; CHECK-CAS-O1-NEXT:    mov v0.d[0], x11
-; CHECK-CAS-O1-NEXT:    mov v0.d[1], x10
+; CHECK-CAS-O1-NEXT:    mov v0.d[0], x10
+; CHECK-CAS-O1-NEXT:    mov v0.d[1], x8
 ; CHECK-CAS-O1-NEXT:    str q0, [x3]
 ; CHECK-CAS-O1-NEXT:    ret
 ;
diff --git a/llvm/test/CodeGen/AArch64/GlobalISel/postlegalizercombiner-select.mir b/llvm/test/CodeGen/AArch64/GlobalISel/postlegalizercombiner-select.mir
new file mode 100644
--- /dev/null
+++ b/llvm/test/CodeGen/AArch64/GlobalISel/postlegalizercombiner-select.mir
@@ -0,0 +1,67 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc -run-pass=aarch64-postlegalizer-combiner -verify-machineinstrs -mtriple aarch64-unknown-unknown %s -o - | FileCheck %s
+---
+# select (c, x, x) -> x
+name:            test_combine_select_same_res
+legalized:       true
+body:             |
+  bb.1:
+    liveins: $x0, $x1
+    ; CHECK-LABEL: name: test_combine_select_same_res
+    ; CHECK: [[COPY:%[0-9]+]]:_(s64) = COPY $x0
+    ; CHECK: [[TRUNC:%[0-9]+]]:_(s1) = G_TRUNC [[COPY]](s64)
+    ; CHECK: [[SELECT:%[0-9]+]]:_(s64) = G_SELECT [[TRUNC]](s1), [[COPY]], [[COPY]]
+    ; CHECK: $x0 = COPY [[SELECT]](s64)
+    %0:_(s64) = COPY $x0
+    %1:_(s1) = G_TRUNC %0
+    %2:_(s64) = G_SELECT %1, %0, %0
+    $x0 = COPY %2(s64)
+...
+---
+# select (undef, x, y) -> y
+name:            test_combine_select_undef_res0_res1
+legalized:       true
+body:             |
+  bb.1:
+    liveins: $x0, $x1
+    ; CHECK-LABEL: name: test_combine_select_undef_res0_res1
+    ; CHECK: [[COPY:%[0-9]+]]:_(s64) = COPY $x0
+    ; CHECK: $x0 = COPY [[COPY]](s64)
+    %0:_(s64) = COPY $x0
+    %1:_(s64) = COPY $x1
+    %2:_(s1) = G_IMPLICIT_DEF
+    %3:_(s64) = G_SELECT %2, %0, %1
+    $x0 = COPY %3(s64)
+...
+---
+# select (false, x, y) -> y
+name:            test_combine_select_false_res0_res1
+legalized:       true
+body:             |
+  bb.1:
+    liveins: $x0, $x1
+    ; CHECK-LABEL: name: test_combine_select_false_res0_res1
+    ; CHECK: [[COPY:%[0-9]+]]:_(s64) = COPY $x1
+    ; CHECK: $x0 = COPY [[COPY]](s64)
+    %0:_(s64) = COPY $x0
+    %1:_(s64) = COPY $x1
+    %2:_(s1) = G_CONSTANT i1 false
+    %3:_(s64) = G_SELECT %2, %0, %1
+    $x0 = COPY %3(s64)
+...
+---
+# select (true, x, y) -> x
+name:            test_combine_select_true_res0_res1
+legalized:       true
+body:             |
+  bb.1:
+    liveins: $x0, $x1
+    ; CHECK-LABEL: name: test_combine_select_true_res0_res1
+    ; CHECK: [[COPY:%[0-9]+]]:_(s64) = COPY $x0
+    ; CHECK: $x0 = COPY [[COPY]](s64)
+    %0:_(s64) = COPY $x0
+    %1:_(s64) = COPY $x1
+    %2:_(s1) = G_CONSTANT i1 true
+    %3:_(s64) = G_SELECT %2, %0, %1
+    $x0 = COPY %3(s64)
+...
diff --git a/llvm/test/CodeGen/AArch64/fold-global-offsets.ll b/llvm/test/CodeGen/AArch64/fold-global-offsets.ll
--- a/llvm/test/CodeGen/AArch64/fold-global-offsets.ll
+++ b/llvm/test/CodeGen/AArch64/fold-global-offsets.ll
@@ -132,16 +132,10 @@
 ; GISEL-NEXT:    add x8, x8, :lo12:x3+88
 ; GISEL-NEXT:    mov v0.d[1], x8
 ; GISEL-NEXT:    mov w9, #64
-; GISEL-NEXT:    mov d1, v0.d[1]
+; GISEL-NEXT:    mov d0, v0.d[1]
 ; GISEL-NEXT:    sub x8, x9, #64 // =64
-; GISEL-NEXT:    fmov x10, d1
 ; GISEL-NEXT:    fmov x9, d0
-; GISEL-NEXT:    lsl x11, x10, x8
-; GISEL-NEXT:    lsr x8, x10, x8
-; GISEL-NEXT:    orr x10, x11, x9, lsr #0
-; GISEL-NEXT:    tst wzr, #0x1
-; GISEL-NEXT:    csel x8, x10, x8, ne
-; GISEL-NEXT:    csel x8, x9, x8, ne
+; GISEL-NEXT:    lsr x8, x9, x8
 ; GISEL-NEXT:    ldr w0, [x8, #20]
 ; GISEL-NEXT:    ret