[InstCombine] Fold sub of umin to usub.sat

We were handling sub of umax, but not the conjugated umin case.

https://alive2.llvm.org/ce/z/4fdZfy
https://alive2.llvm.org/ce/z/BhUQBM

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index 0598f75..8a88192 100644 (file)
--- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -2187,12 +2187,23 @@ Instruction *InstCombinerImpl::visitSub(BinaryOperator &I) {
     return replaceInstUsesWith(
         I, Builder.CreateIntrinsic(Intrinsic::usub_sat, {Ty}, {X, Op1}));
 
+  // Op0 - umin(X, Op0) --> usub.sat(Op0, X)
+  if (match(Op1, m_OneUse(m_c_UMin(m_Value(X), m_Specific(Op0)))))
+    return replaceInstUsesWith(
+        I, Builder.CreateIntrinsic(Intrinsic::usub_sat, {Ty}, {Op0, X}));
+
   // Op0 - umax(X, Op0) --> 0 - usub.sat(X, Op0)
   if (match(Op1, m_OneUse(m_c_UMax(m_Value(X), m_Specific(Op0))))) {
     Value *USub = Builder.CreateIntrinsic(Intrinsic::usub_sat, {Ty}, {X, Op0});
     return BinaryOperator::CreateNeg(USub);
   }
 
+  // umin(X, Op1) - Op1 --> 0 - usub.sat(Op1, X)
+  if (match(Op0, m_OneUse(m_c_UMin(m_Value(X), m_Specific(Op1))))) {
+    Value *USub = Builder.CreateIntrinsic(Intrinsic::usub_sat, {Ty}, {Op1, X});
+    return BinaryOperator::CreateNeg(USub);
+  }
+
   // C - ctpop(X) => ctpop(~X) if C is bitwidth
   if (match(Op0, m_SpecificInt(Ty->getScalarSizeInBits())) &&
       match(Op1, m_OneUse(m_Intrinsic<Intrinsic::ctpop>(m_Value(X)))))

diff --git a/llvm/test/Transforms/InstCombine/sub-minmax.ll b/llvm/test/Transforms/InstCombine/sub-minmax.ll
index 5dbf02c..339dd73 100644 (file)
--- a/llvm/test/Transforms/InstCombine/sub-minmax.ll
+++ b/llvm/test/Transforms/InstCombine/sub-minmax.ll
@@ -39,9 +39,8 @@ define i32 @na_minus_max_na_b(i32 %A, i32 %B) {
 
 define i5 @sub_umin(i5 %a, i5 %b) {
 ; CHECK-LABEL: @sub_umin(
-; CHECK-NEXT:    [[UMIN:%.*]] = call i5 @llvm.umin.i5(i5 [[A:%.*]], i5 [[B:%.*]])
-; CHECK-NEXT:    [[R:%.*]] = sub i5 [[A]], [[UMIN]]
-; CHECK-NEXT:    ret i5 [[R]]
+; CHECK-NEXT:    [[TMP1:%.*]] = call i5 @llvm.usub.sat.i5(i5 [[A:%.*]], i5 [[B:%.*]])
+; CHECK-NEXT:    ret i5 [[TMP1]]
 ;
   %umin = call i5 @llvm.umin.i5(i5 %a, i5 %b)
   %r = sub i5 %a, %umin
@@ -50,9 +49,8 @@ define i5 @sub_umin(i5 %a, i5 %b) {
 
 define <2 x i8> @sub_umin_commute_vec(<2 x i8> %a, <2 x i8> %b) {
 ; CHECK-LABEL: @sub_umin_commute_vec(
-; CHECK-NEXT:    [[UMIN:%.*]] = call <2 x i8> @llvm.umin.v2i8(<2 x i8> [[B:%.*]], <2 x i8> [[A:%.*]])
-; CHECK-NEXT:    [[R:%.*]] = sub <2 x i8> [[B]], [[UMIN]]
-; CHECK-NEXT:    ret <2 x i8> [[R]]
+; CHECK-NEXT:    [[TMP1:%.*]] = call <2 x i8> @llvm.usub.sat.v2i8(<2 x i8> [[B:%.*]], <2 x i8> [[A:%.*]])
+; CHECK-NEXT:    ret <2 x i8> [[TMP1]]
 ;
   %umin = call <2 x i8> @llvm.umin.v2i8(<2 x i8> %b, <2 x i8> %a)
   %r = sub <2 x i8> %b, %umin
@@ -569,9 +567,8 @@ define i8 @umax_sub_op1_use(i8 %x, i8 %y) {
 
 define i8 @umin_sub_op1(i8 %x, i8 %y) {
 ; CHECK-LABEL: @umin_sub_op1(
-; CHECK-NEXT:    [[U:%.*]] = call i8 @llvm.umin.i8(i8 [[Y:%.*]], i8 [[X:%.*]])
-; CHECK-NEXT:    [[R:%.*]] = sub i8 [[Y]], [[U]]
-; CHECK-NEXT:    ret i8 [[R]]
+; CHECK-NEXT:    [[TMP1:%.*]] = call i8 @llvm.usub.sat.i8(i8 [[Y:%.*]], i8 [[X:%.*]])
+; CHECK-NEXT:    ret i8 [[TMP1]]
 ;
   %u = call i8 @llvm.umin.i8(i8 %y, i8 %x)
   %r = sub i8 %y, %u
@@ -580,9 +577,8 @@ define i8 @umin_sub_op1(i8 %x, i8 %y) {
 
 define i8 @umin_sub_op1_commute(i8 %x, i8 %y) {
 ; CHECK-LABEL: @umin_sub_op1_commute(
-; CHECK-NEXT:    [[U:%.*]] = call i8 @llvm.umin.i8(i8 [[X:%.*]], i8 [[Y:%.*]])
-; CHECK-NEXT:    [[R:%.*]] = sub i8 [[Y]], [[U]]
-; CHECK-NEXT:    ret i8 [[R]]
+; CHECK-NEXT:    [[TMP1:%.*]] = call i8 @llvm.usub.sat.i8(i8 [[Y:%.*]], i8 [[X:%.*]])
+; CHECK-NEXT:    ret i8 [[TMP1]]
 ;
   %u = call i8 @llvm.umin.i8(i8 %x, i8 %y)
   %r = sub i8 %y, %u
@@ -591,8 +587,8 @@ define i8 @umin_sub_op1_commute(i8 %x, i8 %y) {
 
 define i8 @umin_sub_op0(i8 %x, i8 %y) {
 ; CHECK-LABEL: @umin_sub_op0(
-; CHECK-NEXT:    [[U:%.*]] = call i8 @llvm.umin.i8(i8 [[Y:%.*]], i8 [[X:%.*]])
-; CHECK-NEXT:    [[R:%.*]] = sub i8 [[U]], [[Y]]
+; CHECK-NEXT:    [[TMP1:%.*]] = call i8 @llvm.usub.sat.i8(i8 [[Y:%.*]], i8 [[X:%.*]])
+; CHECK-NEXT:    [[R:%.*]] = sub i8 0, [[TMP1]]
 ; CHECK-NEXT:    ret i8 [[R]]
 ;
   %u = call i8 @llvm.umin.i8(i8 %y, i8 %x)
@@ -602,8 +598,8 @@ define i8 @umin_sub_op0(i8 %x, i8 %y) {
 
 define i8 @umin_sub_op0_commute(i8 %x, i8 %y) {
 ; CHECK-LABEL: @umin_sub_op0_commute(
-; CHECK-NEXT:    [[U:%.*]] = call i8 @llvm.umin.i8(i8 [[X:%.*]], i8 [[Y:%.*]])
-; CHECK-NEXT:    [[R:%.*]] = sub i8 [[U]], [[Y]]
+; CHECK-NEXT:    [[TMP1:%.*]] = call i8 @llvm.usub.sat.i8(i8 [[Y:%.*]], i8 [[X:%.*]])
+; CHECK-NEXT:    [[R:%.*]] = sub i8 0, [[TMP1]]
 ; CHECK-NEXT:    ret i8 [[R]]
 ;
   %u = call i8 @llvm.umin.i8(i8 %x, i8 %y)