DAG: Improve fminimum/fmaximum vector expansion logic (#93579)

First, expandFMINIMUM_FMAXIMUM should be a never-fail API. The client
wanted it expanded, and it can always be expanded. This logic was tied
up with what the VectorLegalizer wanted.
    
Prefer using the min/max opcodes, and unrolling if we don't have a
vselect.
This seems to produce better code in all the changed tests.

Author: arsenm

llvm/lib/CodeGen/SelectionDAG/LegalizeVectorOps.cpp

@@ -992,11 +992,8 @@ void VectorLegalizer::Expand(SDNode *Node, SmallVectorImpl<SDValue> &Results) {
     break;
   case ISD::FMINIMUM:
   case ISD::FMAXIMUM:
-    if (SDValue Expanded = TLI.expandFMINIMUM_FMAXIMUM(Node, DAG)) {
-      Results.push_back(Expanded);
-      return;
-    }
-    break;
+    Results.push_back(TLI.expandFMINIMUM_FMAXIMUM(Node, DAG));
+    return;
   case ISD::SMIN:
   case ISD::SMAX:
   case ISD::UMIN:

llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp

@@ -8427,10 +8427,6 @@ SDValue TargetLowering::expandFMINIMUM_FMAXIMUM(SDNode *N,
   bool IsMax = Opc == ISD::FMAXIMUM;
   SDNodeFlags Flags = N->getFlags();
 
-  if (VT.isVector() &&
-      isOperationLegalOrCustomOrPromote(Opc, VT.getScalarType()))
-    return SDValue();
-
   // First, implement comparison not propagating NaN. If no native fmin or fmax
   // available, use plain select with setcc instead.
   SDValue MinMax;
@@ -8447,6 +8443,9 @@ SDValue TargetLowering::expandFMINIMUM_FMAXIMUM(SDNode *N,
   } else if (isOperationLegalOrCustom(CompOpc, VT)) {
     MinMax = DAG.getNode(CompOpc, DL, VT, LHS, RHS, Flags);
   } else {
+    if (VT.isVector() && !isOperationLegalOrCustom(ISD::VSELECT, VT))
+      return DAG.UnrollVectorOp(N);
+
     // NaN (if exists) will be propagated later, so orderness doesn't matter.
     SDValue Compare =
         DAG.getSetCC(DL, CCVT, LHS, RHS, IsMax ? ISD::SETGT : ISD::SETLT);

llvm/test/CodeGen/AMDGPU/fmaximum3.ll

@@ -554,28 +554,14 @@ define <2 x half> @v_maximum_v2f16(<2 x half> %src0, <2 x half> %src1) {
 ; GFX8-NEXT:    s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
 ; GFX8-NEXT:    v_lshrrev_b32_e32 v2, 16, v1
 ; GFX8-NEXT:    v_lshrrev_b32_e32 v3, 16, v0
-; GFX8-NEXT:    v_cmp_gt_f16_e32 vcc, v3, v2
-; GFX8-NEXT:    v_cndmask_b32_e32 v4, v2, v3, vcc
+; GFX8-NEXT:    v_max_f16_e32 v4, v3, v2
 ; GFX8-NEXT:    v_mov_b32_e32 v5, 0x7e00
 ; GFX8-NEXT:    v_cmp_o_f16_e32 vcc, v3, v2
-; GFX8-NEXT:    v_cndmask_b32_e32 v4, v5, v4, vcc
-; GFX8-NEXT:    v_cmp_class_f16_e64 vcc, v3, 64
-; GFX8-NEXT:    v_cndmask_b32_e32 v3, v4, v3, vcc
-; GFX8-NEXT:    v_cmp_class_f16_e64 vcc, v2, 64
-; GFX8-NEXT:    v_cndmask_b32_e32 v2, v3, v2, vcc
-; GFX8-NEXT:    v_cmp_eq_f16_e32 vcc, 0, v4
-; GFX8-NEXT:    v_cndmask_b32_e32 v2, v4, v2, vcc
-; GFX8-NEXT:    v_cmp_gt_f16_e32 vcc, v0, v1
-; GFX8-NEXT:    v_cndmask_b32_e32 v3, v1, v0, vcc
+; GFX8-NEXT:    v_cndmask_b32_e32 v2, v5, v4, vcc
+; GFX8-NEXT:    v_max_f16_e32 v3, v0, v1
 ; GFX8-NEXT:    v_cmp_o_f16_e32 vcc, v0, v1
-; GFX8-NEXT:    v_cndmask_b32_e32 v3, v5, v3, vcc
-; GFX8-NEXT:    v_cmp_class_f16_e64 vcc, v0, 64
-; GFX8-NEXT:    v_cndmask_b32_e32 v0, v3, v0, vcc
-; GFX8-NEXT:    v_cmp_class_f16_e64 vcc, v1, 64
-; GFX8-NEXT:    v_cndmask_b32_e32 v0, v0, v1, vcc
-; GFX8-NEXT:    v_cmp_eq_f16_e32 vcc, 0, v3
 ; GFX8-NEXT:    v_lshlrev_b32_e32 v2, 16, v2
-; GFX8-NEXT:    v_cndmask_b32_e32 v0, v3, v0, vcc
+; GFX8-NEXT:    v_cndmask_b32_e32 v0, v5, v3, vcc
 ; GFX8-NEXT:    v_or_b32_sdwa v0, v0, v2 dst_sel:DWORD dst_unused:UNUSED_PAD src0_sel:WORD_0 src1_sel:DWORD
 ; GFX8-NEXT:    s_setpc_b64 s[30:31]
 ;
@@ -669,26 +655,9 @@ define <2 x half> @v_maximum_v2f16__nnan(<2 x half> %src0, <2 x half> %src1) {
 ; GFX8-LABEL: v_maximum_v2f16__nnan:
 ; GFX8:       ; %bb.0:
 ; GFX8-NEXT:    s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
-; GFX8-NEXT:    v_lshrrev_b32_e32 v2, 16, v1
-; GFX8-NEXT:    v_lshrrev_b32_e32 v3, 16, v0
-; GFX8-NEXT:    v_cmp_gt_f16_e32 vcc, v3, v2
-; GFX8-NEXT:    v_cndmask_b32_e32 v4, v2, v3, vcc
-; GFX8-NEXT:    v_cmp_class_f16_e64 vcc, v3, 64
-; GFX8-NEXT:    v_cndmask_b32_e32 v3, v4, v3, vcc
-; GFX8-NEXT:    v_cmp_class_f16_e64 vcc, v2, 64
-; GFX8-NEXT:    v_cndmask_b32_e32 v2, v3, v2, vcc
-; GFX8-NEXT:    v_cmp_eq_f16_e32 vcc, 0, v4
-; GFX8-NEXT:    v_cndmask_b32_e32 v2, v4, v2, vcc
-; GFX8-NEXT:    v_cmp_gt_f16_e32 vcc, v0, v1
-; GFX8-NEXT:    v_cndmask_b32_e32 v3, v1, v0, vcc
-; GFX8-NEXT:    v_cmp_class_f16_e64 vcc, v0, 64
-; GFX8-NEXT:    v_cndmask_b32_e32 v0, v3, v0, vcc
-; GFX8-NEXT:    v_cmp_class_f16_e64 vcc, v1, 64
-; GFX8-NEXT:    v_cndmask_b32_e32 v0, v0, v1, vcc
-; GFX8-NEXT:    v_cmp_eq_f16_e32 vcc, 0, v3
-; GFX8-NEXT:    v_lshlrev_b32_e32 v2, 16, v2
-; GFX8-NEXT:    v_cndmask_b32_e32 v0, v3, v0, vcc
-; GFX8-NEXT:    v_or_b32_sdwa v0, v0, v2 dst_sel:DWORD dst_unused:UNUSED_PAD src0_sel:WORD_0 src1_sel:DWORD
+; GFX8-NEXT:    v_max_f16_sdwa v2, v0, v1 dst_sel:WORD_1 dst_unused:UNUSED_PAD src0_sel:WORD_1 src1_sel:WORD_1
+; GFX8-NEXT:    v_max_f16_e32 v0, v0, v1
+; GFX8-NEXT:    v_or_b32_e32 v0, v0, v2
 ; GFX8-NEXT:    s_setpc_b64 s[30:31]
 ;
 ; GFX9-LABEL: v_maximum_v2f16__nnan:
@@ -754,13 +723,11 @@ define <2 x half> @v_maximum_v2f16__nsz(<2 x half> %src0, <2 x half> %src1) {
 ; GFX8-NEXT:    s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
 ; GFX8-NEXT:    v_lshrrev_b32_e32 v2, 16, v1
 ; GFX8-NEXT:    v_lshrrev_b32_e32 v3, 16, v0
-; GFX8-NEXT:    v_cmp_gt_f16_e32 vcc, v3, v2
-; GFX8-NEXT:    v_cndmask_b32_e32 v4, v2, v3, vcc
+; GFX8-NEXT:    v_max_f16_e32 v4, v3, v2
 ; GFX8-NEXT:    v_mov_b32_e32 v5, 0x7e00
 ; GFX8-NEXT:    v_cmp_o_f16_e32 vcc, v3, v2
 ; GFX8-NEXT:    v_cndmask_b32_e32 v2, v5, v4, vcc
-; GFX8-NEXT:    v_cmp_gt_f16_e32 vcc, v0, v1
-; GFX8-NEXT:    v_cndmask_b32_e32 v3, v1, v0, vcc
+; GFX8-NEXT:    v_max_f16_e32 v3, v0, v1
 ; GFX8-NEXT:    v_cmp_o_f16_e32 vcc, v0, v1
 ; GFX8-NEXT:    v_lshlrev_b32_e32 v2, 16, v2
 ; GFX8-NEXT:    v_cndmask_b32_e32 v0, v5, v3, vcc
@@ -857,14 +824,9 @@ define <2 x half> @v_maximum_v2f16__nnan_nsz(<2 x half> %src0, <2 x half> %src1)
 ; GFX8-LABEL: v_maximum_v2f16__nnan_nsz:
 ; GFX8:       ; %bb.0:
 ; GFX8-NEXT:    s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
-; GFX8-NEXT:    v_lshrrev_b32_e32 v2, 16, v1
-; GFX8-NEXT:    v_lshrrev_b32_e32 v3, 16, v0
-; GFX8-NEXT:    v_cmp_gt_f16_e32 vcc, v3, v2
-; GFX8-NEXT:    v_cndmask_b32_e32 v2, v2, v3, vcc
-; GFX8-NEXT:    v_cmp_gt_f16_e32 vcc, v0, v1
-; GFX8-NEXT:    v_lshlrev_b32_e32 v2, 16, v2
-; GFX8-NEXT:    v_cndmask_b32_e32 v0, v1, v0, vcc
-; GFX8-NEXT:    v_or_b32_sdwa v0, v0, v2 dst_sel:DWORD dst_unused:UNUSED_PAD src0_sel:WORD_0 src1_sel:DWORD
+; GFX8-NEXT:    v_max_f16_sdwa v2, v0, v1 dst_sel:WORD_1 dst_unused:UNUSED_PAD src0_sel:WORD_1 src1_sel:WORD_1
+; GFX8-NEXT:    v_max_f16_e32 v0, v0, v1
+; GFX8-NEXT:    v_or_b32_e32 v0, v0, v2
 ; GFX8-NEXT:    s_setpc_b64 s[30:31]
 ;
 ; GFX9-LABEL: v_maximum_v2f16__nnan_nsz:
@@ -938,31 +900,15 @@ define void @s_maximum_v2f16(<2 x half> inreg %src0, <2 x half> inreg %src1) {
 ; GFX8-NEXT:    s_lshr_b32 s6, s5, 16
 ; GFX8-NEXT:    s_lshr_b32 s7, s4, 16
 ; GFX8-NEXT:    v_mov_b32_e32 v0, s6
-; GFX8-NEXT:    v_mov_b32_e32 v1, s7
-; GFX8-NEXT:    v_cmp_gt_f16_e32 vcc, s7, v0
-; GFX8-NEXT:    v_cndmask_b32_e32 v2, v0, v1, vcc
-; GFX8-NEXT:    v_mov_b32_e32 v3, 0x7e00
+; GFX8-NEXT:    v_max_f16_e32 v1, s7, v0
+; GFX8-NEXT:    v_mov_b32_e32 v2, 0x7e00
 ; GFX8-NEXT:    v_cmp_o_f16_e32 vcc, s7, v0
-; GFX8-NEXT:    v_cndmask_b32_e32 v2, v3, v2, vcc
-; GFX8-NEXT:    v_cmp_class_f16_e64 vcc, s7, 64
-; GFX8-NEXT:    v_cndmask_b32_e32 v1, v2, v1, vcc
-; GFX8-NEXT:    v_cmp_class_f16_e64 vcc, s6, 64
-; GFX8-NEXT:    v_cndmask_b32_e32 v0, v1, v0, vcc
-; GFX8-NEXT:    v_cmp_eq_f16_e32 vcc, 0, v2
+; GFX8-NEXT:    v_cndmask_b32_e32 v0, v2, v1, vcc
 ; GFX8-NEXT:    v_mov_b32_e32 v1, s5
-; GFX8-NEXT:    v_cndmask_b32_e32 v0, v2, v0, vcc
-; GFX8-NEXT:    v_mov_b32_e32 v2, s4
-; GFX8-NEXT:    v_cmp_gt_f16_e32 vcc, s4, v1
-; GFX8-NEXT:    v_cndmask_b32_e32 v4, v1, v2, vcc
+; GFX8-NEXT:    v_max_f16_e32 v3, s4, v1
 ; GFX8-NEXT:    v_cmp_o_f16_e32 vcc, s4, v1
-; GFX8-NEXT:    v_cndmask_b32_e32 v3, v3, v4, vcc
-; GFX8-NEXT:    v_cmp_class_f16_e64 vcc, s4, 64
-; GFX8-NEXT:    v_cndmask_b32_e32 v2, v3, v2, vcc
-; GFX8-NEXT:    v_cmp_class_f16_e64 vcc, s5, 64
-; GFX8-NEXT:    v_cndmask_b32_e32 v1, v2, v1, vcc
-; GFX8-NEXT:    v_cmp_eq_f16_e32 vcc, 0, v3
 ; GFX8-NEXT:    v_lshlrev_b32_e32 v0, 16, v0
-; GFX8-NEXT:    v_cndmask_b32_e32 v1, v3, v1, vcc
+; GFX8-NEXT:    v_cndmask_b32_e32 v1, v2, v3, vcc
 ; GFX8-NEXT:    v_or_b32_sdwa v0, v1, v0 dst_sel:DWORD dst_unused:UNUSED_PAD src0_sel:WORD_0 src1_sel:DWORD
 ; GFX8-NEXT:    ;;#ASMSTART
 ; GFX8-NEXT:    ; use v0