DAG: Make isKnownNeverNaN partially handle minnum/maxnum

[arsenm]

Summary

Only do the most conservative handling until there
is an agreement on what the actual snan behavior is.

http://lists.llvm.org/pipermail/llvm-dev/2018-July/124770.html

lib/CodeGen/SelectionDAG/SelectionDAG.cpp

bool SelectionDAG::isKnownNeverNaN(SDValue Op, bool SNaN, unsigned Depth) const {
   case ISD::FLOG10:
   case ISD::FPOWI:
   case ISD::FPOW: {
     if (SNaN)
       return true;
     // TODO: Refine on operand
     return false;
   }
-
-  // TODO: Handle FMINNUM/FMAXNUM/FMINNAN/FMAXNAN when there is an agreement on
-  // what they should do.
+  case ISD::FMINNUM:
+  case ISD::FMAXNUM:
+  case ISD::FMINNAN:
+  case ISD::FMAXNAN: {
+    // TODO: This could be better if there was an agreement on snan behavior.
+    return isKnownNeverNaN(Op.getOperand(0), SNaN, Depth + 1) &&
+           isKnownNeverNaN(Op.getOperand(1), SNaN, Depth + 1);
+  }
   default:
     if (Opcode >= ISD::BUILTIN_OP_END ||
         Opcode == ISD::INTRINSIC_WO_CHAIN ||
         Opcode == ISD::INTRINSIC_W_CHAIN ||
         Opcode == ISD::INTRINSIC_VOID) {
       return TLI->isKnownNeverNaNForTargetNode(Op, *this, SNaN, Depth);
     }
 

test/CodeGen/AMDGPU/known-never-snan.ll

 
 define float @v_test_known_not_snan_minnum_input_fmed3_r_i_i_f32(float %a, float %b) #0 {
 ; GCN-LABEL: v_test_known_not_snan_minnum_input_fmed3_r_i_i_f32:
 ; GCN:       ; %bb.0:
 ; GCN-NEXT:    s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
 ; GCN-NEXT:    v_rcp_f32_e32 v0, v0
 ; GCN-NEXT:    v_add_f32_e32 v1, 1.0, v1
 ; GCN-NEXT:    v_min_f32_e32 v0, v0, v1
-; GCN-NEXT:    v_max_f32_e32 v0, 2.0, v0
-; GCN-NEXT:    v_min_f32_e32 v0, 4.0, v0
+; GCN-NEXT:    v_med3_f32 v0, v0, 2.0, 4.0
 ; GCN-NEXT:    s_setpc_b64 s[30:31]
   %a.nnan.add = fdiv nnan float 1.0, %a
   %b.nnan.add = fadd nnan float %b, 1.0
   %known.not.snan = call float @llvm.minnum.f32(float %a.nnan.add, float %b.nnan.add)
   %max = call float @llvm.maxnum.f32(float %known.not.snan, float 2.0)
   %med = call float @llvm.minnum.f32(float %max, float 4.0)
   ret float %med
 }
 
+define float @v_test_known_not_minnum_maybe_nan_src0_input_fmed3_r_i_i_f32(float %a, float %b) #0 {
+; GCN-LABEL: v_test_known_not_minnum_maybe_nan_src0_input_fmed3_r_i_i_f32:
+; GCN:       ; %bb.0:
+; GCN-NEXT:    s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
+; GCN-NEXT:    v_add_f32_e32 v1, 1.0, v1
+; GCN-NEXT:    v_min_f32_e32 v0, v0, v1
+; GCN-NEXT:    v_max_f32_e32 v0, 2.0, v0
+; GCN-NEXT:    v_min_f32_e32 v0, 4.0, v0
+; GCN-NEXT:    s_setpc_b64 s[30:31]
+  %b.nsnan = fadd float %b, 1.0
+  %known.not.snan = call float @llvm.minnum.f32(float %a, float %b.nsnan)
+  %max = call float @llvm.maxnum.f32(float %known.not.snan, float 2.0)
+  %med = call float @llvm.minnum.f32(float %max, float 4.0)
+  ret float %med
+}
+
+define float @v_test_known_not_minnum_maybe_nan_src1_input_fmed3_r_i_i_f32(float %a, float %b) #0 {
+; GCN-LABEL: v_test_known_not_minnum_maybe_nan_src1_input_fmed3_r_i_i_f32:
+; GCN:       ; %bb.0:
+; GCN-NEXT:    s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
+; GCN-NEXT:    v_add_f32_e32 v0, 1.0, v0
+; GCN-NEXT:    v_min_f32_e32 v0, v0, v1
+; GCN-NEXT:    v_max_f32_e32 v0, 2.0, v0
+; GCN-NEXT:    v_min_f32_e32 v0, 4.0, v0
+; GCN-NEXT:    s_setpc_b64 s[30:31]
+  %a.nsnan = fadd float %a, 1.0
+  %known.not.snan = call float @llvm.minnum.f32(float %a.nsnan, float %b)
+  %max = call float @llvm.maxnum.f32(float %known.not.snan, float 2.0)
+  %med = call float @llvm.minnum.f32(float %max, float 4.0)
+  ret float %med
+}
+
 define float @v_minnum_possible_nan_lhs_input_fmed3_r_i_i_f32(float %a, float %b) #0 {
 ; GCN-LABEL: v_minnum_possible_nan_lhs_input_fmed3_r_i_i_f32:
 ; GCN:       ; %bb.0:
 ; GCN-NEXT:    s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
 ; GCN-NEXT:    v_add_f32_e32 v1, 1.0, v1
 ; GCN-NEXT:    v_min_f32_e32 v0, v0, v1
 ; GCN-NEXT:    v_max_f32_e32 v0, 2.0, v0
 ; GCN-NEXT:    v_min_f32_e32 v0, 4.0, v0

 }
 
 define float @v_test_known_not_snan_maxnum_input_fmed3_r_i_i_f32(float %a, float %b) #0 {
 ; GCN-LABEL: v_test_known_not_snan_maxnum_input_fmed3_r_i_i_f32:
 ; GCN:       ; %bb.0:
 ; GCN-NEXT:    s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
 ; GCN-NEXT:    v_rcp_f32_e32 v0, v0
 ; GCN-NEXT:    v_add_f32_e32 v1, 1.0, v1
-; GCN-NEXT:    v_max3_f32 v0, v0, v1, 2.0
-; GCN-NEXT:    v_min_f32_e32 v0, 4.0, v0
+; GCN-NEXT:    v_max_f32_e32 v0, v0, v1
+; GCN-NEXT:    v_med3_f32 v0, v0, 2.0, 4.0
 ; GCN-NEXT:    s_setpc_b64 s[30:31]
   %a.nnan.add = fdiv nnan float 1.0, %a
   %b.nnan.add = fadd nnan float %b, 1.0
   %known.not.snan = call float @llvm.maxnum.f32(float %a.nnan.add, float %b.nnan.add)
   %max = call float @llvm.maxnum.f32(float %known.not.snan, float 2.0)
   %med = call float @llvm.minnum.f32(float %max, float 4.0)
   ret float %med
 }