[Matrix] Propagate shape information through Select insts

[jroelofs]

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[llvmbot]

@llvm/pr-subscribers-llvm-transforms

Author: Jon Roelofs (jroelofs)

Changes

---

Full diff: https://github.com/llvm/llvm-project/pull/141876.diff

2 Files Affected:

• (modified) llvm/lib/Transforms/Scalar/LowerMatrixIntrinsics.cpp (+47-1)
• (added) llvm/test/Transforms/LowerMatrixIntrinsics/select.ll (+26)

diff --git a/llvm/lib/Transforms/Scalar/LowerMatrixIntrinsics.cpp b/llvm/lib/Transforms/Scalar/LowerMatrixIntrinsics.cpp
index 756a72e6d97bc..6cfe077b602d3 100644
--- a/llvm/lib/Transforms/Scalar/LowerMatrixIntrinsics.cpp
+++ b/llvm/lib/Transforms/Scalar/LowerMatrixIntrinsics.cpp
@@ -269,6 +269,15 @@ computeShapeInfoForInst(Instruction *I,
       return OpShape->second;
   }
 
+  if (isa<SelectInst>(I)) {
+    auto OpShape = ShapeMap.find(I->getOperand(1));
+    if (OpShape != ShapeMap.end())
+      return OpShape->second;
+    OpShape = ShapeMap.find(I->getOperand(2));
+    if (OpShape != ShapeMap.end())
+      return OpShape->second;
+  }
+
   if (isUniformShape(I)) {
     // Find the first operand that has a known shape and use that.
     for (auto &Op : I->operands()) {
@@ -623,7 +632,7 @@ class LowerMatrixIntrinsics {
       default:
         return false;
       }
-    return isUniformShape(V) || isa<StoreInst>(V) || isa<LoadInst>(V);
+    return isUniformShape(V) || isa<StoreInst>(V) || isa<LoadInst>(V) || isa<SelectInst>(V);
   }
 
   /// Propagate the shape information of instructions to their users.
@@ -710,6 +719,12 @@ class LowerMatrixIntrinsics {
       } else if (isa<StoreInst>(V)) {
         // Nothing to do.  We forward-propagated to this so we would just
         // backward propagate to an instruction with an already known shape.
+      } else if (auto *Select = dyn_cast<SelectInst>(V)) {
+        ShapeInfo Shape = ShapeMap[V];
+        if (setShapeInfo(Select->getOperand(1), Shape))
+          pushInstruction(Select, WorkList);
+        if (setShapeInfo(Select->getOperand(2), Shape))
+          pushInstruction(Select, WorkList);
       } else if (isUniformShape(V)) {
         // Propagate to all operands.
         ShapeInfo Shape = ShapeMap[V];
@@ -1068,6 +1083,8 @@ class LowerMatrixIntrinsics {
         Changed |= VisitBinaryOperator(BinOp);
       if (auto *UnOp = dyn_cast<UnaryOperator>(Inst))
         Changed |= VisitUnaryOperator(UnOp);
+      if (auto *Select = dyn_cast<SelectInst>(Inst))
+        Changed |= VisitSelectInst(Select);
       if (match(Inst, m_Load(m_Value(Op1))))
         Changed |= VisitLoad(cast<LoadInst>(Inst), Op1, Builder);
       else if (match(Inst, m_Store(m_Value(Op1), m_Value(Op2))))
@@ -2198,6 +2215,35 @@ class LowerMatrixIntrinsics {
     return true;
   }
 
+  /// Lower selects, if shape information is available.
+  bool VisitSelectInst(SelectInst *Inst) {
+    auto I = ShapeMap.find(Inst);
+    if (I == ShapeMap.end())
+      return false;
+
+    Value *Cond = Inst->getOperand(0);
+    Value *OpA = Inst->getOperand(1);
+    Value *OpB = Inst->getOperand(2);
+
+    IRBuilder<> Builder(Inst);
+    ShapeInfo &Shape = I->second;
+
+    MatrixTy Result;
+    MatrixTy A = getMatrix(OpA, Shape, Builder);
+    MatrixTy B = getMatrix(OpB, Shape, Builder);
+
+    for (unsigned I = 0; I < Shape.getNumVectors(); ++I) {
+      auto *Sel = Builder.CreateSelect(Cond, A.getVector(I), B.getVector(I));
+      Result.addVector(Sel);
+    }
+
+    finalizeLowering(Inst,
+                     Result.addNumComputeOps(getNumOps(Result.getVectorTy()) *
+                                             Result.getNumVectors()),
+                     Builder);
+    return true;
+  }
+
   /// Helper to linearize a matrix expression tree into a string. Currently
   /// matrix expressions are linarized by starting at an expression leaf and
   /// linearizing bottom up.
diff --git a/llvm/test/Transforms/LowerMatrixIntrinsics/select.ll b/llvm/test/Transforms/LowerMatrixIntrinsics/select.ll
new file mode 100644
index 0000000000000..acfd9228ee17a
--- /dev/null
+++ b/llvm/test/Transforms/LowerMatrixIntrinsics/select.ll
@@ -0,0 +1,26 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -passes='lower-matrix-intrinsics' -S < %s | FileCheck %s
+
+define void @select_2x2(i1 %cond, ptr %lhs, ptr %rhs, ptr %out) {
+; CHECK-LABEL: @select_2x2(
+; CHECK-NEXT:    [[COL_LOAD:%.*]] = load <2 x float>, ptr [[LHS:%.*]], align 16
+; CHECK-NEXT:    [[VEC_GEP:%.*]] = getelementptr float, ptr [[LHS]], i64 2
+; CHECK-NEXT:    [[COL_LOAD1:%.*]] = load <2 x float>, ptr [[VEC_GEP]], align 8
+; CHECK-NEXT:    [[COL_LOAD2:%.*]] = load <2 x float>, ptr [[RHS:%.*]], align 16
+; CHECK-NEXT:    [[VEC_GEP3:%.*]] = getelementptr float, ptr [[RHS]], i64 2
+; CHECK-NEXT:    [[COL_LOAD4:%.*]] = load <2 x float>, ptr [[VEC_GEP3]], align 8
+; CHECK-NEXT:    [[TMP1:%.*]] = select i1 [[COND:%.*]], <2 x float> [[COL_LOAD]], <2 x float> [[COL_LOAD2]]
+; CHECK-NEXT:    [[TMP2:%.*]] = select i1 [[COND]], <2 x float> [[COL_LOAD1]], <2 x float> [[COL_LOAD4]]
+; CHECK-NEXT:    store <2 x float> [[TMP1]], ptr [[OUT:%.*]], align 16
+; CHECK-NEXT:    [[VEC_GEP5:%.*]] = getelementptr float, ptr [[OUT]], i64 2
+; CHECK-NEXT:    store <2 x float> [[TMP2]], ptr [[VEC_GEP5]], align 8
+; CHECK-NEXT:    ret void
+;
+  %lhsv = load <4 x float>, ptr %lhs
+  %rhsv = load <4 x float>, ptr %rhs
+  %op = select i1 %cond, <4 x float> %lhsv, <4 x float> %rhsv
+  %opt  = call <4 x float> @llvm.matrix.transpose(<4 x float> %op, i32 2, i32 2)
+  %optt = call <4 x float> @llvm.matrix.transpose(<4 x float> %opt, i32 2, i32 2)
+  store <4 x float> %optt, ptr %out
+  ret void
+}

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