Address review comments

Author: ckoparkar

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -6200,21 +6200,11 @@ SDValue DAGCombiner::visitIMINMAX(SDNode *N) {
     return SD;
 
   // (umin (sub a, b) a) -> (usubo a, b); (select usubo.1, a, usubo.0)
-  //
-  // IR:
-  //   %sub  = sub %a, %b
-  //   %cond = umin %sub, %a
-  //   ->
-  //   %usubo    = usubo %a, %b
-  //   %overflow = extractvalue %usubo, 1
-  //   %sub      = extractvalue %usubo, 0
-  //   %cond     = select %overflow, %a, %sub
   if (N0.getOpcode() == ISD::SUB) {
-    SDValue A, B, C;
-    if (sd_match(N, m_UMin(m_Sub(m_Value(A), m_Value(B)), m_Value(C)))) {
-      EVT AVT = A.getValueType();
-      if (A == C && TLI.isOperationLegalOrCustom(ISD::USUBO, AVT)) {
-        SDVTList VTs = DAG.getVTList(AVT, MVT::i1);
+    SDValue A, B;
+    if (sd_match(N, m_UMin(m_Sub(m_Value(A), m_Value(B)), m_Deferred(A)))) {
+      if (TLI.isOperationLegalOrCustom(ISD::USUBO, VT)) {
+        SDVTList VTs = DAG.getVTList(VT, MVT::i1);
         SDValue USO = DAG.getNode(ISD::USUBO, DL, VTs, A, B);
         return DAG.getSelect(DL, VT, USO.getValue(1), A, USO.getValue(0));
       }

llvm/test/CodeGen/AArch64/underflow-compare-fold.ll

@@ -0,0 +1,14 @@
+; RUN: llc < %s -mtriple=aarch64 | FileCheck %s
+
+; GitHub issue #161036
+
+define i64 @underflow_compare_fold(i64 %a, i64 %b) {
+; CHECK-LABEL: underflow_compare_fold
+; CHECK:      // %bb.0:
+; CHECK-NEXT: subs x8, x0, x1
+; CHECK-NEXT: csel x0, x0, x8, lo
+; CHECK-NEXT: ret
+  %sub = sub i64 %a, %b
+  %cond = tail call i64 @llvm.umin.i64(i64 %sub, i64 %a)
+  ret i64 %cond
+}

llvm/test/CodeGen/X86/underflow-compare-fold.ll

@@ -2,14 +2,13 @@
 
 ; GitHub issue #161036
 
-define i64 @subIfNoUnderflow_umin(i64 %a, i64 %b) {
-; CHECK-LABEL: subIfNoUnderflow_umin
+define i64 @underflow_compare_fold(i64 %a, i64 %b) {
+; CHECK-LABEL: underflow_compare_fold
 ; CHECK-LABEL: %bb.0
 ; CHECK-NEXT: movq    %rdi, %rax
 ; CHECK-NEXT: subq    %rsi, %rax
 ; CHECK-NEXT: cmovbq  %rdi, %rax
 ; CHECK-NEXT: retq
-entry:
   %sub = sub i64 %a, %b
   %cond = tail call i64 @llvm.umin.i64(i64 %sub, i64 %a)
   ret i64 %cond