[AMDGPU][GISel] Add missing V2S16 BUILD_VECTOR_TRUNC legalization

[Pierre-vh]

Summary

Previously we would be unable to legalize V2S16 BUILD_VECTOR_TRUNC on GFX8 & below as the custom legalization was missing.

[arsenm]

llvm/lib/Target/AMDGPU/AMDGPULegalizerInfo.cpp

2901–2902

Src0 = B.buildTrunc(S16, ...).getReg(0)

llvm/test/CodeGen/AMDGPU/GlobalISel/legalize-build-vector-trunc.mir

6

Should add a bonaire run line too

[Pierre-vh]

Comments

[arsenm]

llvm/lib/Target/AMDGPU/AMDGPULegalizerInfo.cpp

2904–2905

These asserts are redundant. The verifier or asserts in buildMerge would catch this being wrong

llvm/lib/Target/AMDGPU/AMDGPULegalizerInfo.cpp

case TargetOpcode::G_FLOG10:
     return legalizeFlog(MI, B, numbers::ln2f / numbers::ln10f);
   case TargetOpcode::G_FEXP:
     return legalizeFExp(MI, B);
   case TargetOpcode::G_FPOW:
     return legalizeFPow(MI, B);
   case TargetOpcode::G_FFLOOR:
     return legalizeFFloor(MI, MRI, B);
   case TargetOpcode::G_BUILD_VECTOR:
+  case TargetOpcode::G_BUILD_VECTOR_TRUNC:
     return legalizeBuildVector(MI, MRI, B);
   case TargetOpcode::G_MUL:
     return legalizeMul(Helper, MI);
   case TargetOpcode::G_CTLZ:
   case TargetOpcode::G_CTTZ:
     return legalizeCTLZ_CTTZ(MI, MRI, B);
   case TargetOpcode::G_INTRINSIC_FPTRUNC_ROUND:
     return legalizeFPTruncRound(MI, B);

 }
 
 // Turn an illegal packed v2s16 build vector into bit operations.
 // TODO: This should probably be a bitcast action in LegalizerHelper.
 bool AMDGPULegalizerInfo::legalizeBuildVector(
   MachineInstr &MI, MachineRegisterInfo &MRI, MachineIRBuilder &B) const {
   Register Dst = MI.getOperand(0).getReg();
   const LLT S32 = LLT::scalar(32);
+  const LLT S16 = LLT::scalar(16);
   assert(MRI.getType(Dst) == LLT::fixed_vector(2, 16));
 
   Register Src0 = MI.getOperand(1).getReg();
   Register Src1 = MI.getOperand(2).getReg();
-  assert(MRI.getType(Src0) == LLT::scalar(16));
+
+  if (MI.getOpcode() == AMDGPU::G_BUILD_VECTOR_TRUNC) {
+    assert(MRI.getType(Src0) == S32);
+
+    Src0 = MRI.createGenericVirtualRegister(S16);
+    B.buildTrunc(Src0, MI.getOperand(1).getReg());
+
+    Src1 = MRI.createGenericVirtualRegister(S16);
+    B.buildTrunc(Src1, MI.getOperand(2).getReg());
+  }
+
+  assert(MRI.getType(Src0) == S16);
+  assert(MRI.getType(Src1) == S16);
 
   auto Merge = B.buildMerge(S32, {Src0, Src1});
   B.buildBitcast(Dst, Merge);
 
   MI.eraseFromParent();
   return true;
 }
 

llvm/test/CodeGen/AMDGPU/GlobalISel/legalize-build-vector-trunc.mir

 # NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
 # RUN: llc -mtriple=amdgcn-amd-amdhsa -mcpu=gfx900 -O0 -run-pass=legalizer %s -o - | FileCheck -check-prefix=GFX9 %s
 # RUN: llc -mtriple=amdgcn-amd-amdhsa -mcpu=gfx1010 -O0 -run-pass=legalizer %s -o - | FileCheck -check-prefix=GFX9 %s
 # RUN: llc -mtriple=amdgcn-amd-amdhsa -mcpu=gfx1100 -O0 -run-pass=legalizer %s -o - | FileCheck -check-prefix=GFX9 %s
+# RUN: llc -mtriple=amdgcn-amd-amdhsa -mcpu=fiji -O0 -run-pass=legalizer %s -o - | FileCheck -check-prefix=VI %s
 
 ---
 name: legal_s32_to_v2s16
 body: |
   bb.0:
     liveins: $vgpr0, $vgpr1
 
     ; GFX9-LABEL: name: legal_s32_to_v2s16
     ; GFX9: liveins: $vgpr0, $vgpr1
     ; GFX9-NEXT: {{  $}}
     ; GFX9-NEXT: [[COPY:%[0-9]+]]:_(s32) = COPY $vgpr0
     ; GFX9-NEXT: [[COPY1:%[0-9]+]]:_(s32) = COPY $vgpr1
     ; GFX9-NEXT: [[BUILD_VECTOR_TRUNC:%[0-9]+]]:_(<2 x s16>) = G_BUILD_VECTOR_TRUNC [[COPY]](s32), [[COPY1]](s32)
     ; GFX9-NEXT: S_NOP 0, implicit [[BUILD_VECTOR_TRUNC]](<2 x s16>)
+    ; VI-LABEL: name: legal_s32_to_v2s16
+    ; VI: liveins: $vgpr0, $vgpr1
+    ; VI-NEXT: {{  $}}
+    ; VI-NEXT: [[COPY:%[0-9]+]]:_(s32) = COPY $vgpr0
+    ; VI-NEXT: [[COPY1:%[0-9]+]]:_(s32) = COPY $vgpr1
+    ; VI-NEXT: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 65535
+    ; VI-NEXT: [[AND:%[0-9]+]]:_(s32) = G_AND [[COPY]], [[C]]
+    ; VI-NEXT: [[AND1:%[0-9]+]]:_(s32) = G_AND [[COPY1]], [[C]]
+    ; VI-NEXT: [[C1:%[0-9]+]]:_(s32) = G_CONSTANT i32 16
+    ; VI-NEXT: [[SHL:%[0-9]+]]:_(s32) = G_SHL [[AND1]], [[C1]](s32)
+    ; VI-NEXT: [[OR:%[0-9]+]]:_(s32) = G_OR [[AND]], [[SHL]]
+    ; VI-NEXT: [[BITCAST:%[0-9]+]]:_(<2 x s16>) = G_BITCAST [[OR]](s32)
+    ; VI-NEXT: S_NOP 0, implicit [[BITCAST]](<2 x s16>)
     %0:_(s32) = COPY $vgpr0
     %1:_(s32) = COPY $vgpr1
     %2:_(<2 x s16>) = G_BUILD_VECTOR_TRUNC %0, %1
     S_NOP 0, implicit %2
 ...