[RISCV] Match fmaxnum and fminnum to reduction ops. (#159244)

This patch tries to match fmaxnum and fminnum to vector reductions.

Author: tclin914

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

@@ -15144,6 +15144,10 @@ static unsigned getVecReduceOpcode(unsigned Opc) {
   case ISD::FADD:
     // Note: This is the associative form of the generic reduction opcode.
     return ISD::VECREDUCE_FADD;
+  case ISD::FMAXNUM:
+    return ISD::VECREDUCE_FMAX;
+  case ISD::FMINNUM:
+    return ISD::VECREDUCE_FMIN;
   }
 }
 
@@ -15172,13 +15176,22 @@ combineBinOpOfExtractToReduceTree(SDNode *N, SelectionDAG &DAG,
   const EVT VT = N->getValueType(0);
   const unsigned Opc = N->getOpcode();
 
-  // For FADD, we only handle the case with reassociation allowed.  We
-  // could handle strict reduction order, but at the moment, there's no
-  // known reason to, and the complexity isn't worth it.
-  // TODO: Handle fminnum and fmaxnum here
-  if (!VT.isInteger() &&
-      (Opc != ISD::FADD || !N->getFlags().hasAllowReassociation()))
-    return SDValue();
+  if (!VT.isInteger()) {
+    switch (Opc) {
+    default:
+      return SDValue();
+    case ISD::FADD:
+      // For FADD, we only handle the case with reassociation allowed.  We
+      // could handle strict reduction order, but at the moment, there's no
+      // known reason to, and the complexity isn't worth it.
+      if (!N->getFlags().hasAllowReassociation())
+        return SDValue();
+      break;
+    case ISD::FMAXNUM:
+    case ISD::FMINNUM:
+      break;
+    }
+  }
 
   const unsigned ReduceOpc = getVecReduceOpcode(Opc);
   assert(Opc == ISD::getVecReduceBaseOpcode(ReduceOpc) &&

llvm/test/CodeGen/RISCV/rvv/fixed-vectors-reduction-formation.ll

@@ -904,3 +904,33 @@ define float @reduce_fadd_4xi32_non_associative2(ptr %p) {
   %fadd2 = fadd fast float %fadd1, %e3
   ret float %fadd2
 }
+
+define float @reduce_fmaxnum_16xf32_prefix2(ptr %p) {
+; CHECK-LABEL: reduce_fmaxnum_16xf32_prefix2:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    vsetivli zero, 2, e32, mf2, ta, ma
+; CHECK-NEXT:    vle32.v v8, (a0)
+; CHECK-NEXT:    vfredmax.vs v8, v8, v8
+; CHECK-NEXT:    vfmv.f.s fa0, v8
+; CHECK-NEXT:    ret
+  %v = load <16 x float>, ptr %p, align 256
+  %e0 = extractelement <16 x float> %v, i32 0
+  %e1 = extractelement <16 x float> %v, i32 1
+  %fmax0 = call float @llvm.maxnum.f32(float %e0, float %e1)
+  ret float %fmax0
+}
+
+define float @reduce_fminnum_16xf32_prefix2(ptr %p) {
+; CHECK-LABEL: reduce_fminnum_16xf32_prefix2:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    vsetivli zero, 2, e32, mf2, ta, ma
+; CHECK-NEXT:    vle32.v v8, (a0)
+; CHECK-NEXT:    vfredmin.vs v8, v8, v8
+; CHECK-NEXT:    vfmv.f.s fa0, v8
+; CHECK-NEXT:    ret
+  %v = load <16 x float>, ptr %p, align 256
+  %e0 = extractelement <16 x float> %v, i32 0
+  %e1 = extractelement <16 x float> %v, i32 1
+  %fmax0 = call float @llvm.minnum.f32(float %e0, float %e1)
+  ret float %fmax0
+}