[InstSimplify] allow partial undef constants for vector min/max folds

Author: rotateright

llvm/lib/Analysis/InstructionSimplify.cpp

@@ -5266,16 +5266,15 @@ static Value *simplifyBinaryIntrinsic(Function *F, Value *Op0, Value *Op1,
     if (isa<Constant>(Op0))
       std::swap(Op0, Op1);
 
-    // TODO: Allow partial undef vector constants.
     const APInt *C;
-    if (!match(Op1, m_APInt(C)))
+    if (!match(Op1, m_APIntAllowUndef(C)))
       break;
 
     if ((IID == Intrinsic::smax && C->isMaxSignedValue()) ||
         (IID == Intrinsic::smin && C->isMinSignedValue()) ||
         (IID == Intrinsic::umax && C->isMaxValue()) ||
         (IID == Intrinsic::umin && C->isMinValue()))
-      return Op1;
+      return ConstantInt::get(ReturnType, *C);
 
     break;
   }

llvm/test/Transforms/InstSimplify/maxmin_intrinsics.ll

@@ -218,35 +218,31 @@ define <2 x i8> @umin_maxval_commute(<2 x i8> %x) {
 
 define <2 x i8> @smax_maxval_partial_undef(<2 x i8> %x) {
 ; CHECK-LABEL: @smax_maxval_partial_undef(
-; CHECK-NEXT:    [[R:%.*]] = call <2 x i8> @llvm.smax.v2i8(<2 x i8> <i8 undef, i8 127>, <2 x i8> [[X:%.*]])
-; CHECK-NEXT:    ret <2 x i8> [[R]]
+; CHECK-NEXT:    ret <2 x i8> <i8 127, i8 127>
 ;
   %r = call <2 x i8> @llvm.smax.v2i8(<2 x i8> <i8 undef, i8 127>, <2 x i8> %x)
   ret <2 x i8> %r
 }
 
 define <2 x i8> @smin_minval_partial_undef(<2 x i8> %x) {
 ; CHECK-LABEL: @smin_minval_partial_undef(
-; CHECK-NEXT:    [[R:%.*]] = call <2 x i8> @llvm.smin.v2i8(<2 x i8> [[X:%.*]], <2 x i8> <i8 -128, i8 undef>)
-; CHECK-NEXT:    ret <2 x i8> [[R]]
+; CHECK-NEXT:    ret <2 x i8> <i8 -128, i8 -128>
 ;
   %r = call <2 x i8> @llvm.smin.v2i8(<2 x i8> %x, <2 x i8> <i8 -128, i8 undef>)
   ret <2 x i8> %r
 }
 
 define <2 x i8> @umax_maxval_partial_undef(<2 x i8> %x) {
 ; CHECK-LABEL: @umax_maxval_partial_undef(
-; CHECK-NEXT:    [[R:%.*]] = call <2 x i8> @llvm.umax.v2i8(<2 x i8> <i8 -1, i8 undef>, <2 x i8> [[X:%.*]])
-; CHECK-NEXT:    ret <2 x i8> [[R]]
+; CHECK-NEXT:    ret <2 x i8> <i8 -1, i8 -1>
 ;
   %r = call <2 x i8> @llvm.umax.v2i8(<2 x i8> <i8 255, i8 undef>, <2 x i8> %x)
   ret <2 x i8> %r
 }
 
 define <2 x i8> @umin_minval_partial_undef(<2 x i8> %x) {
 ; CHECK-LABEL: @umin_minval_partial_undef(
-; CHECK-NEXT:    [[R:%.*]] = call <2 x i8> @llvm.umin.v2i8(<2 x i8> [[X:%.*]], <2 x i8> <i8 undef, i8 0>)
-; CHECK-NEXT:    ret <2 x i8> [[R]]
+; CHECK-NEXT:    ret <2 x i8> zeroinitializer
 ;
   %r = call <2 x i8> @llvm.umin.v2i8(<2 x i8> %x, <2 x i8> <i8 undef, i8 0>)
   ret <2 x i8> %r