[llvm] DAG: Fix assuming f16 is the only 16-bit fp type in concat vector combine (PR #121637)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-selectiondag

Author: Matt Arsenault (arsenm)

<details>
<summary>Changes</summary>

Fixes #<!-- -->121601

---
Full diff: https://github.com/llvm/llvm-project/pull/121637.diff


2 Files Affected:

- (modified) llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp (+13-17) 
- (added) llvm/test/CodeGen/AMDGPU/issue121601-combine-concat-vectors-assumes-f16.ll (+19) 


``````````diff
diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 6b2501591c81a3..9ef0660bf07199 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -24291,8 +24291,8 @@ static SDValue combineConcatVectorOfScalars(SDNode *N, SelectionDAG &DAG) {
   EVT SVT = EVT::getIntegerVT(*DAG.getContext(), OpVT.getSizeInBits());
 
   // Keep track of what we encounter.
-  bool AnyInteger = false;
-  bool AnyFP = false;
+  EVT AnyFPVT;
+
   for (const SDValue &Op : N->ops()) {
     if (ISD::BITCAST == Op.getOpcode() &&
         !Op.getOperand(0).getValueType().isVector())
@@ -24306,27 +24306,23 @@ static SDValue combineConcatVectorOfScalars(SDNode *N, SelectionDAG &DAG) {
     // If it's neither, bail out, it could be something weird like x86mmx.
     EVT LastOpVT = Ops.back().getValueType();
     if (LastOpVT.isFloatingPoint())
-      AnyFP = true;
-    else if (LastOpVT.isInteger())
-      AnyInteger = true;
-    else
+      AnyFPVT = LastOpVT;
+    else if (!LastOpVT.isInteger())
       return SDValue();
   }
 
   // If any of the operands is a floating point scalar bitcast to a vector,
   // use floating point types throughout, and bitcast everything.
   // Replace UNDEFs by another scalar UNDEF node, of the final desired type.
-  if (AnyFP) {
-    SVT = EVT::getFloatingPointVT(OpVT.getSizeInBits());
-    if (AnyInteger) {
-      for (SDValue &Op : Ops) {
-        if (Op.getValueType() == SVT)
-          continue;
-        if (Op.isUndef())
-          Op = DAG.getNode(ISD::UNDEF, DL, SVT);
-        else
-          Op = DAG.getBitcast(SVT, Op);
-      }
+  if (AnyFPVT != EVT()) {
+    SVT = AnyFPVT;
+    for (SDValue &Op : Ops) {
+      if (Op.getValueType() == SVT)
+        continue;
+      if (Op.isUndef())
+        Op = DAG.getNode(ISD::UNDEF, DL, SVT);
+      else
+        Op = DAG.getBitcast(SVT, Op);
     }
   }
 
diff --git a/llvm/test/CodeGen/AMDGPU/issue121601-combine-concat-vectors-assumes-f16.ll b/llvm/test/CodeGen/AMDGPU/issue121601-combine-concat-vectors-assumes-f16.ll
new file mode 100644
index 00000000000000..1a87887e28d72e
--- /dev/null
+++ b/llvm/test/CodeGen/AMDGPU/issue121601-combine-concat-vectors-assumes-f16.ll
@@ -0,0 +1,19 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
+; RUN: llc -mtriple=amdgcn-amd-amdhsa -mcpu=gfx942 < %s | FileCheck %s
+
+define <4 x float> @issue121601(bfloat %fptrunc) {
+; CHECK-LABEL: issue121601:
+; CHECK:       ; %bb.0: ; %bb
+; CHECK-NEXT:    s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
+; CHECK-NEXT:    v_lshlrev_b32_e32 v0, 16, v0
+; CHECK-NEXT:    v_mov_b32_e32 v1, v0
+; CHECK-NEXT:    v_mov_b32_e32 v2, 0
+; CHECK-NEXT:    v_mov_b32_e32 v3, 0
+; CHECK-NEXT:    s_setpc_b64 s[30:31]
+bb:
+  %bitcast = bitcast bfloat %fptrunc to <1 x bfloat>
+  %shufflevector = shufflevector <1 x bfloat> %bitcast, <1 x bfloat> zeroinitializer, <2 x i32> zeroinitializer
+  %fpext = fpext <2 x bfloat> %shufflevector to <2 x float>
+  %shufflevector1 = shufflevector <2 x float> %fpext, <2 x float> zeroinitializer, <4 x i32> <i32 0, i32 1, i32 2, i32 3>
+  ret <4 x float> %shufflevector1
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/121637