[InstCombine] Optimize sub(sext(add(x,y)),sext(add(x,z))).

llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp

@@ -2807,6 +2807,62 @@ Instruction *InstCombinerImpl::visitSub(BinaryOperator &I) {
   if (Instruction *Res = foldBinOpOfSelectAndCastOfSelectCondition(I))
     return Res;
 
+  // (sub[ nsw][ nuw] (sext (add nsw (X, Y)), sext (X))) --> (sext (Y))
+  {
+    Value *Add0;
+    if (match(Op0, m_SExt(m_Value(Add0))) &&
+        match(Add0, m_Add(m_Value(X), m_Value(Y))) &&
+        match(Op1, m_SExt(m_Specific(X)))) {
+      auto *OBO0 = cast<OverflowingBinaryOperator>(Add0);
+      if (OBO0->hasNoSignedWrap()) {
+        // Non-constant Y requires new SExt.
+        unsigned numOfNewInstrs = !isa<Constant>(Y) ? 1 : 0;
+        // Check if we can trade some of the old instructions for the new ones.
+        unsigned numOfDeadInstrs = 0;
+        numOfDeadInstrs += Op0->hasOneUse() ? 1 : 0;
+        numOfDeadInstrs += Op1->hasOneUse() ? 1 : 0;
+        numOfDeadInstrs += Add0->hasOneUse() ? 1 : 0;
+        if (numOfDeadInstrs >= numOfNewInstrs) {
+          Value *SExtY = Builder.CreateSExt(Y, I.getType());
+          return replaceInstUsesWith(I, SExtY);
+        }
+      }
+    }
+  }
+
+  // (sub[ nsw] (sext (add nsw (X, Y)), sext (add nsw (X, Z)))) -->
+  // --> (sub[ nsw] (sext (Y), sext(Z)))
+  {
+    Value *Z, *Add0, *Add1;
+    if (match(Op0, m_SExt(m_Value(Add0))) &&
+        match(Add0, m_Add(m_Value(X), m_Value(Y))) &&
+        match(Op1, m_SExt(m_Value(Add1))) &&
+        match(Add1, m_Add(m_Specific(X), m_Value(Z)))) {
+      auto *OBO0 = cast<OverflowingBinaryOperator>(Add0);
+      auto *OBO1 = cast<OverflowingBinaryOperator>(Add1);
+      if (OBO0->hasNoSignedWrap() && OBO1->hasNoSignedWrap()) {
+        unsigned numOfNewInstrs = 0;
+        // Non-constant Y, Z require new SExt.
+        numOfNewInstrs += !isa<Constant>(Y) ? 1 : 0;
+        numOfNewInstrs += !isa<Constant>(Z) ? 1 : 0;
+        // Check if we can trade some of the old instructions for the new ones.
+        unsigned numOfDeadInstrs = 0;
+        numOfDeadInstrs += Op0->hasOneUse() ? 1 : 0;
+        numOfDeadInstrs += Op1->hasOneUse() ? 1 : 0;
+        numOfDeadInstrs += Add0->hasOneUse() ? 1 : 0;
+        numOfDeadInstrs += Add1->hasOneUse() ? 1 : 0;
+        if (numOfDeadInstrs >= numOfNewInstrs) {
+          Value *SExtY = Builder.CreateSExt(Y, I.getType());
+          Value *SExtZ = Builder.CreateSExt(Z, I.getType());
+          Value *Sub = Builder.CreateSub(SExtY, SExtZ, "",
+                                         /* HasNUW */ false,
+                                         /* HasNSW */ I.hasNoSignedWrap());
+          return replaceInstUsesWith(I, Sub);
+        }
+      }
+    }
+  }
+
   return TryToNarrowDeduceFlags();
 }
 

llvm/test/Transforms/InstCombine/sub-sext-add.ll

@@ -0,0 +1,89 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -passes=instcombine -S | FileCheck %s
+
+define i64 @src_2add_2sext_sub(i32 %x, i32 %y, i32 %z) {
+; CHECK-LABEL: define i64 @src_2add_2sext_sub(
+; CHECK-SAME: i32 [[X:%.*]], i32 [[Y:%.*]], i32 [[Z:%.*]]) {
+; CHECK-NEXT:    [[SEXT1:%.*]] = sext i32 [[Y]] to i64
+; CHECK-NEXT:    [[SEXT2:%.*]] = sext i32 [[Z]] to i64
+; CHECK-NEXT:    [[SUB:%.*]] = sub nsw i64 [[SEXT1]], [[SEXT2]]
+; CHECK-NEXT:    ret i64 [[SUB]]
+;
+  %add1 = add nsw i32 %x, %y
+  %add2 = add nsw i32 %x, %z
+  %sext1 = sext i32 %add1 to i64
+  %sext2 = sext i32 %add2 to i64
+  %sub = sub i64 %sext1, %sext2
+  ret i64 %sub
+}
+
+define i64 @src_2add_2sext_sub_nsw(i32 %x, i32 %y, i32 %z) {
+; CHECK-LABEL: define i64 @src_2add_2sext_sub_nsw(
+; CHECK-SAME: i32 [[X:%.*]], i32 [[Y:%.*]], i32 [[Z:%.*]]) {
+; CHECK-NEXT:    [[SEXT1:%.*]] = sext i32 [[Y]] to i64
+; CHECK-NEXT:    [[SEXT2:%.*]] = sext i32 [[Z]] to i64
+; CHECK-NEXT:    [[SUB:%.*]] = sub nsw i64 [[SEXT1]], [[SEXT2]]
+; CHECK-NEXT:    ret i64 [[SUB]]
+;
+  %add1 = add nsw i32 %x, %y
+  %add2 = add nsw i32 %x, %z
+  %sext1 = sext i32 %add1 to i64
+  %sext2 = sext i32 %add2 to i64
+  %sub = sub nsw i64 %sext1, %sext2
+  ret i64 %sub
+}
+
+define i64 @src_2add_2sext_sub_nuw(i32 %x, i32 %y, i32 %z) {
+; CHECK-LABEL: define i64 @src_2add_2sext_sub_nuw(
+; CHECK-SAME: i32 [[X:%.*]], i32 [[Y:%.*]], i32 [[Z:%.*]]) {
+; CHECK-NEXT:    [[TMP1:%.*]] = sext i32 [[Y]] to i64
+; CHECK-NEXT:    [[TMP2:%.*]] = sext i32 [[Z]] to i64
+; CHECK-NEXT:    [[SUB:%.*]] = sub nsw i64 [[TMP1]], [[TMP2]]
+; CHECK-NEXT:    ret i64 [[SUB]]
+;
+  %add1 = add nsw i32 %x, %y
+  %add2 = add nsw i32 %x, %z
+  %sext1 = sext i32 %add1 to i64
+  %sext2 = sext i32 %add2 to i64
+  %sub = sub nuw i64 %sext1, %sext2
+  ret i64 %sub
+}
+
+define i64 @src_x_add_2sext_sub(i32 %x, i32 %y) {
+; CHECK-LABEL: define i64 @src_x_add_2sext_sub(
+; CHECK-SAME: i32 [[X:%.*]], i32 [[Y:%.*]]) {
+; CHECK-NEXT:    [[SUB:%.*]] = sext i32 [[Y]] to i64
+; CHECK-NEXT:    ret i64 [[SUB]]
+;
+  %add1 = add nsw i32 %x, %y
+  %sext1 = sext i32 %add1 to i64
+  %sext2 = sext i32 %x to i64
+  %sub = sub i64 %sext1, %sext2
+  ret i64 %sub
+}
+
+define i64 @src_x_add_2sext_sub_nsw(i32 %x, i32 %y) {
+; CHECK-LABEL: define i64 @src_x_add_2sext_sub_nsw(
+; CHECK-SAME: i32 [[X:%.*]], i32 [[Y:%.*]]) {
+; CHECK-NEXT:    [[SUB:%.*]] = sext i32 [[Y]] to i64
+; CHECK-NEXT:    ret i64 [[SUB]]
+;
+  %add1 = add nsw i32 %x, %y
+  %sext1 = sext i32 %add1 to i64
+  %sext2 = sext i32 %x to i64
+  %sub = sub nsw i64 %sext1, %sext2
+  ret i64 %sub
+}
+
+define i64 @src_x_add_2sext_sub_nuw(i32 %x, i32 %y) {
+; CHECK-LABEL: define i64 @src_x_add_2sext_sub_nuw(
+; CHECK-SAME: i32 [[X:%.*]], i32 [[Y:%.*]]) {
+; CHECK-NEXT:    [[SUB:%.*]] = sext i32 [[Y]] to i64
+; CHECK-NEXT:    ret i64 [[SUB]]
+;
+  %add1 = add nsw i32 %x, %y
+  %sext1 = sext i32 %add1 to i64
+  %sext2 = sext i32 %x to i64
+  %sub = sub nuw i64 %sext1, %sext2
+  ret i64 %sub
+}