Index: lib/CodeGen/GlobalISel/LegalizerHelper.cpp
===================================================================
--- lib/CodeGen/GlobalISel/LegalizerHelper.cpp
+++ lib/CodeGen/GlobalISel/LegalizerHelper.cpp
@@ -861,6 +861,46 @@
     widenScalarDst(MI, WideTy.getScalarType(), 0);
     return Legalized;
   }
+  case TargetOpcode::G_MERGE_VALUES: {
+    if (TypeIdx != 1)
+      return UnableToLegalize;
+
+    unsigned DstReg = MI.getOperand(0).getReg();
+    LLT DstTy = MRI.getType(DstReg);
+    if (!DstTy.isScalar())
+      return UnableToLegalize;
+
+    unsigned NumSrc = MI.getNumOperands() - 1;
+    unsigned EltSize = DstTy.getSizeInBits() / NumSrc;
+    LLT EltTy = LLT::scalar(EltSize);
+
+    unsigned ResultReg = MRI.createGenericVirtualRegister(DstTy);
+    unsigned Offset = 0;
+    for (unsigned I = 1, E = MI.getNumOperands(); I != E; ++I,
+           Offset += EltSize) {
+      assert(MRI.getType(MI.getOperand(I).getReg()) == EltTy);
+
+      unsigned ShiftAmt = MRI.createGenericVirtualRegister(DstTy);
+      unsigned Shl = MRI.createGenericVirtualRegister(DstTy);
+      unsigned ZextInput = MRI.createGenericVirtualRegister(DstTy);
+      MIRBuilder.buildZExt(ZextInput, MI.getOperand(I).getReg());
+
+      if (Offset != 0) {
+        unsigned NextResult = I + 1 == E ? DstReg :
+          MRI.createGenericVirtualRegister(DstTy);
+
+        MIRBuilder.buildConstant(ShiftAmt, Offset);
+        MIRBuilder.buildShl(Shl, ZextInput, ShiftAmt);
+        MIRBuilder.buildOr(NextResult, ResultReg, Shl);
+        ResultReg = NextResult;
+      } else {
+        ResultReg = ZextInput;
+      }
+    }
+
+    MI.eraseFromParent();
+    return Legalized;
+  }
   case TargetOpcode::G_UADDO:
   case TargetOpcode::G_USUBO: {
     if (TypeIdx == 1)
Index: lib/Target/AMDGPU/AMDGPULegalizerInfo.cpp
===================================================================
--- lib/Target/AMDGPU/AMDGPULegalizerInfo.cpp
+++ lib/Target/AMDGPU/AMDGPULegalizerInfo.cpp
@@ -184,7 +184,8 @@
     .legalFor({{S64, S32}, {S32, S16}, {S64, S16},
                {S32, S1}, {S64, S1}, {S16, S1},
                // FIXME: Hack
-               {S128, S32}, {S128, S64}})
+               {S128, S32}, {S128, S64}, {S32, LLT::scalar(24)}})
+
     .scalarize(0);
 
   getActionDefinitionsBuilder({G_SITOFP, G_UITOFP})
@@ -508,6 +509,13 @@
     };
 
     getActionDefinitionsBuilder(Op)
+      .widenScalarToNextPow2(LitTyIdx, /*Min*/ 16)
+      // Clamp the little scalar to s8-s256 and make it a power of 2. It's not
+      // worth considering the multiples of 64 since 2*192 and 2*384 are not
+      // valid.
+      .clampScalar(LitTyIdx, S16, S256)
+      .widenScalarToNextPow2(LitTyIdx, /*Min*/ 32)
+
       // Break up vectors with weird elements into scalars
       .fewerElementsIf(
         [=](const LegalityQuery &Query) { return notValidElt(Query, 0); },
@@ -534,12 +542,6 @@
           }
           return std::make_pair(BigTyIdx, LLT::scalar(NewSizeInBits));
         })
-      .widenScalarToNextPow2(LitTyIdx, /*Min*/ 16)
-      // Clamp the little scalar to s8-s256 and make it a power of 2. It's not
-      // worth considering the multiples of 64 since 2*192 and 2*384 are not
-      // valid.
-      .clampScalar(LitTyIdx, S16, S256)
-      .widenScalarToNextPow2(LitTyIdx, /*Min*/ 32)
       .legalIf([=](const LegalityQuery &Query) {
           const LLT &BigTy = Query.Types[BigTyIdx];
           const LLT &LitTy = Query.Types[LitTyIdx];
Index: test/CodeGen/AArch64/GlobalISel/legalize-merge-values.mir
===================================================================
--- test/CodeGen/AArch64/GlobalISel/legalize-merge-values.mir
+++ test/CodeGen/AArch64/GlobalISel/legalize-merge-values.mir
@@ -1,30 +1,37 @@
-# RUN: llc -O0 -run-pass=legalizer -global-isel-abort=0 -pass-remarks-missed='gisel*' %s -o - 2>&1 | FileCheck %s
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc  -march=aarch64 -O0 -run-pass=legalizer  %s -o - | FileCheck %s
 
---- |
-  target datalayout = "e-m:o-i64:64-i128:128-n32:64-S128"
-  target triple = "aarch64--"
-  define void @test_merge_s4() {
-    ret void
-  }
-...
+# Previously, LegalizerInfo was assuming all G_MERGE_VALUES and G_UNMERGE_VALUES
+# instructions are legal. Make sure that is no longer happening.
 
 ---
 name:            test_merge_s4
-registers:
-  - { id: 0, class: _ }
-  - { id: 1, class: _ }
-  - { id: 2, class: _ }
-  - { id: 3, class: _ }
-  - { id: 4, class: _ }
 body: |
   bb.0:
-    %0(s64) = G_CONSTANT i64 0
-    %1(s4) = G_TRUNC %0(s64)
-    ; Previously, LegalizerInfo was assuming all G_MERGE_VALUES and G_UNMERGE_VALUES
-    ; instructions are legal. Make sure that is no longer happening.
-    ; CHECK: unable to legalize instruction: {{.*}} G_MERGE_VALUES
-    %2(s8) = G_MERGE_VALUES %1(s4), %1(s4)
-    %3(s8) = COPY %2(s8)
-    %4(s64) = G_ANYEXT %3(s8)
-    $x0 = COPY %4(s64)
+    ; CHECK-LABEL: name: test_merge_s4
+    ; CHECK: [[C:%[0-9]+]]:_(s64) = G_CONSTANT i64 0
+    ; CHECK: [[C1:%[0-9]+]]:_(s32) = G_CONSTANT i32 4
+    ; CHECK: [[C2:%[0-9]+]]:_(s32) = G_CONSTANT i32 15
+    ; CHECK: [[TRUNC:%[0-9]+]]:_(s32) = G_TRUNC [[C]](s64)
+    ; CHECK: [[AND:%[0-9]+]]:_(s32) = G_AND [[TRUNC]], [[C2]]
+    ; CHECK: [[C3:%[0-9]+]]:_(s32) = G_CONSTANT i32 255
+    ; CHECK: [[COPY:%[0-9]+]]:_(s32) = COPY [[C1]](s32)
+    ; CHECK: [[AND1:%[0-9]+]]:_(s32) = G_AND [[COPY]], [[C3]]
+    ; CHECK: [[SHL:%[0-9]+]]:_(s32) = G_SHL [[AND]], [[AND1]](s32)
+    ; CHECK: [[C4:%[0-9]+]]:_(s32) = G_CONSTANT i32 15
+    ; CHECK: [[TRUNC1:%[0-9]+]]:_(s32) = G_TRUNC [[C]](s64)
+    ; CHECK: [[AND2:%[0-9]+]]:_(s32) = G_AND [[TRUNC1]], [[C4]]
+    ; CHECK: [[COPY1:%[0-9]+]]:_(s32) = COPY [[SHL]](s32)
+    ; CHECK: [[OR:%[0-9]+]]:_(s32) = G_OR [[AND2]], [[COPY1]]
+    ; CHECK: [[TRUNC2:%[0-9]+]]:_(s8) = G_TRUNC [[OR]](s32)
+    ; CHECK: [[COPY2:%[0-9]+]]:_(s8) = COPY [[TRUNC2]](s8)
+    ; CHECK: [[ANYEXT:%[0-9]+]]:_(s64) = G_ANYEXT [[COPY2]](s8)
+    ; CHECK: $x0 = COPY [[ANYEXT]](s64)
+    %0:_(s64) = G_CONSTANT i64 0
+    %1:_(s4) = G_TRUNC %0
+
+    %2:_(s8) = G_MERGE_VALUES %1, %1
+    %3:_(s8) = COPY %2
+    %4:_(s64) = G_ANYEXT %3
+    $x0 = COPY %4
 ...
Index: test/CodeGen/AMDGPU/GlobalISel/legalize-merge-values.mir
===================================================================
--- /dev/null
+++ test/CodeGen/AMDGPU/GlobalISel/legalize-merge-values.mir
@@ -0,0 +1,156 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc -mtriple=amdgcn-mesa-mesa3d -mcpu=tahiti -O0 -run-pass=legalizer %s -o - | FileCheck %s
+
+---
+name: test_merge_s16_s8_s8
+body: |
+  bb.0:
+    ; CHECK-LABEL: name: test_merge_s16_s8_s8
+    ; CHECK: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 0
+    ; CHECK: [[C1:%[0-9]+]]:_(s32) = G_CONSTANT i32 1
+    ; CHECK: [[C2:%[0-9]+]]:_(s32) = G_CONSTANT i32 8
+    ; CHECK: [[C3:%[0-9]+]]:_(s32) = G_CONSTANT i32 255
+    ; CHECK: [[COPY:%[0-9]+]]:_(s32) = COPY [[C1]](s32)
+    ; CHECK: [[AND:%[0-9]+]]:_(s32) = G_AND [[COPY]], [[C3]]
+    ; CHECK: [[C4:%[0-9]+]]:_(s32) = G_CONSTANT i32 65535
+    ; CHECK: [[COPY1:%[0-9]+]]:_(s32) = COPY [[C2]](s32)
+    ; CHECK: [[AND1:%[0-9]+]]:_(s32) = G_AND [[COPY1]], [[C4]]
+    ; CHECK: [[SHL:%[0-9]+]]:_(s32) = G_SHL [[AND]], [[AND1]](s32)
+    ; CHECK: [[C5:%[0-9]+]]:_(s32) = G_CONSTANT i32 255
+    ; CHECK: [[COPY2:%[0-9]+]]:_(s32) = COPY [[C]](s32)
+    ; CHECK: [[AND2:%[0-9]+]]:_(s32) = G_AND [[COPY2]], [[C5]]
+    ; CHECK: [[COPY3:%[0-9]+]]:_(s32) = COPY [[SHL]](s32)
+    ; CHECK: [[OR:%[0-9]+]]:_(s32) = G_OR [[AND2]], [[COPY3]]
+    ; CHECK: [[COPY4:%[0-9]+]]:_(s32) = COPY [[OR]](s32)
+    ; CHECK: $vgpr0 = COPY [[COPY4]](s32)
+    %0:_(s8) = G_CONSTANT i8 0
+    %1:_(s8) = G_CONSTANT i8 1
+    %2:_(s16) = G_MERGE_VALUES %0, %1
+    %3:_(s32) = G_ANYEXT %2
+    $vgpr0 = COPY %3
+...
+
+---
+name: test_merge_s24_s8_s8_s8
+body: |
+  bb.0:
+    ; CHECK-LABEL: name: test_merge_s24_s8_s8_s8
+    ; CHECK: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 0
+    ; CHECK: [[C1:%[0-9]+]]:_(s32) = G_CONSTANT i32 1
+    ; CHECK: [[C2:%[0-9]+]]:_(s32) = G_CONSTANT i32 2
+    ; CHECK: [[C3:%[0-9]+]]:_(s32) = G_CONSTANT i32 8
+    ; CHECK: [[C4:%[0-9]+]]:_(s32) = G_CONSTANT i32 255
+    ; CHECK: [[COPY:%[0-9]+]]:_(s32) = COPY [[C1]](s32)
+    ; CHECK: [[AND:%[0-9]+]]:_(s32) = G_AND [[COPY]], [[C4]]
+    ; CHECK: [[C5:%[0-9]+]]:_(s32) = G_CONSTANT i32 16777215
+    ; CHECK: [[COPY1:%[0-9]+]]:_(s32) = COPY [[C3]](s32)
+    ; CHECK: [[AND1:%[0-9]+]]:_(s32) = G_AND [[COPY1]], [[C5]]
+    ; CHECK: [[SHL:%[0-9]+]]:_(s32) = G_SHL [[AND]], [[AND1]](s32)
+    ; CHECK: [[C6:%[0-9]+]]:_(s32) = G_CONSTANT i32 255
+    ; CHECK: [[COPY2:%[0-9]+]]:_(s32) = COPY [[C]](s32)
+    ; CHECK: [[AND2:%[0-9]+]]:_(s32) = G_AND [[COPY2]], [[C6]]
+    ; CHECK: [[COPY3:%[0-9]+]]:_(s32) = COPY [[SHL]](s32)
+    ; CHECK: [[OR:%[0-9]+]]:_(s32) = G_OR [[AND2]], [[COPY3]]
+    ; CHECK: [[C7:%[0-9]+]]:_(s32) = G_CONSTANT i32 16
+    ; CHECK: [[C8:%[0-9]+]]:_(s32) = G_CONSTANT i32 255
+    ; CHECK: [[COPY4:%[0-9]+]]:_(s32) = COPY [[C2]](s32)
+    ; CHECK: [[AND3:%[0-9]+]]:_(s32) = G_AND [[COPY4]], [[C8]]
+    ; CHECK: [[C9:%[0-9]+]]:_(s32) = G_CONSTANT i32 16777215
+    ; CHECK: [[COPY5:%[0-9]+]]:_(s32) = COPY [[C7]](s32)
+    ; CHECK: [[AND4:%[0-9]+]]:_(s32) = G_AND [[COPY5]], [[C9]]
+    ; CHECK: [[SHL1:%[0-9]+]]:_(s32) = G_SHL [[AND3]], [[AND4]](s32)
+    ; CHECK: [[COPY6:%[0-9]+]]:_(s32) = COPY [[OR]](s32)
+    ; CHECK: [[COPY7:%[0-9]+]]:_(s32) = COPY [[SHL1]](s32)
+    ; CHECK: [[OR1:%[0-9]+]]:_(s32) = G_OR [[COPY6]], [[COPY7]]
+    ; CHECK: [[COPY8:%[0-9]+]]:_(s32) = COPY [[OR1]](s32)
+    ; CHECK: $vgpr0 = COPY [[COPY8]](s32)
+    %0:_(s8) = G_CONSTANT i8 0
+    %1:_(s8) = G_CONSTANT i8 1
+    %2:_(s8) = G_CONSTANT i8 2
+    %3:_(s24) = G_MERGE_VALUES %0, %1, %2
+    %4:_(s32) = G_ANYEXT %3
+    $vgpr0 = COPY %4
+...
+
+---
+name: test_merge_s32_s8_s8_s8_s8
+body: |
+  bb.0:
+    ; CHECK-LABEL: name: test_merge_s32_s8_s8_s8_s8
+    ; CHECK: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 0
+    ; CHECK: [[C1:%[0-9]+]]:_(s32) = G_CONSTANT i32 1
+    ; CHECK: [[C2:%[0-9]+]]:_(s32) = G_CONSTANT i32 2
+    ; CHECK: [[C3:%[0-9]+]]:_(s32) = G_CONSTANT i32 3
+    ; CHECK: [[C4:%[0-9]+]]:_(s32) = G_CONSTANT i32 255
+    ; CHECK: [[COPY:%[0-9]+]]:_(s32) = COPY [[C]](s32)
+    ; CHECK: [[AND:%[0-9]+]]:_(s32) = G_AND [[COPY]], [[C4]]
+    ; CHECK: [[C5:%[0-9]+]]:_(s32) = G_CONSTANT i32 255
+    ; CHECK: [[COPY1:%[0-9]+]]:_(s32) = COPY [[C1]](s32)
+    ; CHECK: [[AND1:%[0-9]+]]:_(s32) = G_AND [[COPY1]], [[C5]]
+    ; CHECK: [[C6:%[0-9]+]]:_(s32) = G_CONSTANT i32 8
+    ; CHECK: [[SHL:%[0-9]+]]:_(s32) = G_SHL [[AND1]], [[C6]](s32)
+    ; CHECK: [[OR:%[0-9]+]]:_(s32) = G_OR [[AND]], [[SHL]]
+    ; CHECK: [[C7:%[0-9]+]]:_(s32) = G_CONSTANT i32 255
+    ; CHECK: [[COPY2:%[0-9]+]]:_(s32) = COPY [[C2]](s32)
+    ; CHECK: [[AND2:%[0-9]+]]:_(s32) = G_AND [[COPY2]], [[C7]]
+    ; CHECK: [[C8:%[0-9]+]]:_(s32) = G_CONSTANT i32 16
+    ; CHECK: [[SHL1:%[0-9]+]]:_(s32) = G_SHL [[AND2]], [[C8]](s32)
+    ; CHECK: [[OR1:%[0-9]+]]:_(s32) = G_OR [[OR]], [[SHL1]]
+    ; CHECK: [[C9:%[0-9]+]]:_(s32) = G_CONSTANT i32 255
+    ; CHECK: [[COPY3:%[0-9]+]]:_(s32) = COPY [[C3]](s32)
+    ; CHECK: [[AND3:%[0-9]+]]:_(s32) = G_AND [[COPY3]], [[C9]]
+    ; CHECK: [[C10:%[0-9]+]]:_(s32) = G_CONSTANT i32 24
+    ; CHECK: [[SHL2:%[0-9]+]]:_(s32) = G_SHL [[AND3]], [[C10]](s32)
+    ; CHECK: [[OR2:%[0-9]+]]:_(s32) = G_OR [[OR1]], [[SHL2]]
+    ; CHECK: $vgpr0 = COPY [[OR2]](s32)
+    %0:_(s8) = G_CONSTANT i8 0
+    %1:_(s8) = G_CONSTANT i8 1
+    %2:_(s8) = G_CONSTANT i8 2
+    %3:_(s8) = G_CONSTANT i8 3
+    %4:_(s32) = G_MERGE_VALUES %0, %1, %2, %3
+    $vgpr0 = COPY %4
+...
+
+---
+name: test_merge_s64_s32_s32
+body: |
+  bb.0:
+    liveins: $vgpr0, $vgpr1
+    ; CHECK-LABEL: name: test_merge_s64_s32_s32
+    ; CHECK: [[COPY:%[0-9]+]]:_(s32) = COPY $vgpr0
+    ; CHECK: [[COPY1:%[0-9]+]]:_(s32) = COPY $vgpr1
+    ; CHECK: [[MV:%[0-9]+]]:_(s64) = G_MERGE_VALUES [[COPY]](s32), [[COPY1]](s32)
+    ; CHECK: $vgpr1_vgpr2 = COPY [[MV]](s64)
+    %0:_(s32) = COPY $vgpr0
+    %1:_(s32) = COPY $vgpr1
+    %2:_(s64) = G_MERGE_VALUES %0, %1
+    $vgpr1_vgpr2 = COPY %2
+...
+
+---
+name: test_merge_s64_s16_s16_s16_s16
+body: |
+  bb.0:
+    liveins: $vgpr0, $vgpr1, $vgpr2, $vgpr3
+    ; CHECK-LABEL: name: test_merge_s64_s16_s16_s16_s16
+    ; CHECK: [[COPY:%[0-9]+]]:_(s32) = COPY $vgpr0
+    ; CHECK: [[COPY1:%[0-9]+]]:_(s32) = COPY $vgpr1
+    ; CHECK: [[COPY2:%[0-9]+]]:_(s32) = COPY $vgpr2
+    ; CHECK: [[COPY3:%[0-9]+]]:_(s32) = COPY $vgpr3
+    ; CHECK: [[TRUNC:%[0-9]+]]:_(s16) = G_TRUNC [[COPY]](s32)
+    ; CHECK: [[TRUNC1:%[0-9]+]]:_(s16) = G_TRUNC [[COPY1]](s32)
+    ; CHECK: [[TRUNC2:%[0-9]+]]:_(s16) = G_TRUNC [[COPY2]](s32)
+    ; CHECK: [[TRUNC3:%[0-9]+]]:_(s16) = G_TRUNC [[COPY3]](s32)
+    ; CHECK: [[MV:%[0-9]+]]:_(s64) = G_MERGE_VALUES [[TRUNC]](s16), [[TRUNC1]](s16), [[TRUNC2]](s16), [[TRUNC3]](s16)
+    ; CHECK: $vgpr1_vgpr2 = COPY [[MV]](s64)
+    %0:_(s32) = COPY $vgpr0
+    %1:_(s32) = COPY $vgpr1
+    %2:_(s32) = COPY $vgpr2
+    %3:_(s32) = COPY $vgpr3
+    %4:_(s16) = G_TRUNC %0
+    %5:_(s16) = G_TRUNC %1
+    %6:_(s16) = G_TRUNC %2
+    %7:_(s16) = G_TRUNC %3
+    %8:_(s64) = G_MERGE_VALUES %4, %5, %6, %7
+    $vgpr1_vgpr2 = COPY %8
+...