[AMDGPU] Add InstCombine rule for ballot.i64 intrinsic in wave32 mode. (#71556)

Substitute with zero-extended to i64 ballot.i32 intrinsic.

Author: vpykhtin

clang/test/CodeGenOpenCL/builtins-amdgcn-wave32.cl

@@ -24,23 +24,19 @@ void test_ballot_wave32_target_attr(global uint* out, int a, int b)
 }
 
 // CHECK-LABEL: @test_read_exec(
-// CHECK: call i64 @llvm.amdgcn.ballot.i64(i1 true)
+// CHECK: call i32 @llvm.amdgcn.ballot.i32(i1 true)
 void test_read_exec(global uint* out) {
   *out = __builtin_amdgcn_read_exec();
 }
 
-// CHECK: declare i64 @llvm.amdgcn.ballot.i64(i1) #[[$NOUNWIND_READONLY:[0-9]+]]
-
 // CHECK-LABEL: @test_read_exec_lo(
 // CHECK: call i32 @llvm.amdgcn.ballot.i32(i1 true)
 void test_read_exec_lo(global uint* out) {
   *out = __builtin_amdgcn_read_exec_lo();
 }
 
 // CHECK-LABEL: @test_read_exec_hi(
-// CHECK: call i64 @llvm.amdgcn.ballot.i64(i1 true)
-// CHECK: lshr i64 [[A:%.*]], 32
-// CHECK: trunc i64 [[B:%.*]] to i32
+// CHECK: store i32 0, ptr addrspace(1) %out
 void test_read_exec_hi(global uint* out) {
   *out = __builtin_amdgcn_read_exec_hi();
 }

llvm/lib/Target/AMDGPU/AMDGPUISelDAGToDAG.cpp

@@ -2382,7 +2382,7 @@ void AMDGPUDAGToDAGISel::SelectBRCOND(SDNode *N) {
     auto CC = cast<CondCodeSDNode>(Cond->getOperand(2))->get();
     if ((CC == ISD::SETEQ || CC == ISD::SETNE) &&
         isNullConstant(Cond->getOperand(1)) &&
-        // TODO: make condition below an assert after fixing ballot bitwidth.
+        // We may encounter ballot.i64 in wave32 mode on -O0.
         VCMP.getValueType().getSizeInBits() == ST->getWavefrontSize()) {
       // %VCMP = i(WaveSize) AMDGPUISD::SETCC ...
       // %C = i1 ISD::SETCC %VCMP, 0, setne/seteq

llvm/lib/Target/AMDGPU/AMDGPUInstCombineIntrinsic.cpp

@@ -990,6 +990,19 @@ GCNTTIImpl::instCombineIntrinsic(InstCombiner &IC, IntrinsicInst &II) const {
         return IC.replaceInstUsesWith(II, Constant::getNullValue(II.getType()));
       }
     }
+    if (ST->isWave32() && II.getType()->getIntegerBitWidth() == 64) {
+      // %b64 = call i64 ballot.i64(...)
+      // =>
+      // %b32 = call i32 ballot.i32(...)
+      // %b64 = zext i32 %b32 to i64
+      Value *Call = IC.Builder.CreateZExt(
+          IC.Builder.CreateIntrinsic(Intrinsic::amdgcn_ballot,
+                                     {IC.Builder.getInt32Ty()},
+                                     {II.getArgOperand(0)}),
+          II.getType());
+      Call->takeName(&II);
+      return IC.replaceInstUsesWith(II, Call);
+    }
     break;
   }
   case Intrinsic::amdgcn_wqm_vote: {

llvm/test/Transforms/InstCombine/AMDGPU/amdgcn-intrinsics.ll

@@ -2599,7 +2599,8 @@ declare i32 @llvm.amdgcn.ballot.i32(i1) nounwind readnone convergent
 
 define i64 @ballot_nocombine_64(i1 %i) {
 ; CHECK-LABEL: @ballot_nocombine_64(
-; CHECK-NEXT:    [[B:%.*]] = call i64 @llvm.amdgcn.ballot.i64(i1 [[I:%.*]])
+; CHECK-NEXT:    [[TMP1:%.*]] = call i32 @llvm.amdgcn.ballot.i32(i1 [[I:%.*]])
+; CHECK-NEXT:    [[B:%.*]] = zext i32 [[TMP1]] to i64
 ; CHECK-NEXT:    ret i64 [[B]]
 ;
   %b = call i64 @llvm.amdgcn.ballot.i64(i1 %i)
@@ -2616,7 +2617,8 @@ define i64 @ballot_zero_64() {
 
 define i64 @ballot_one_64() {
 ; CHECK-LABEL: @ballot_one_64(
-; CHECK-NEXT:    [[B:%.*]] = call i64 @llvm.amdgcn.ballot.i64(i1 true)
+; CHECK-NEXT:    [[TMP1:%.*]] = call i32 @llvm.amdgcn.ballot.i32(i1 true)
+; CHECK-NEXT:    [[B:%.*]] = zext i32 [[TMP1]] to i64
 ; CHECK-NEXT:    ret i64 [[B]]
 ;
   %b = call i64 @llvm.amdgcn.ballot.i64(i1 1)