[InstCombine] Fold its select user into select for true value

Refactor with a lambda function to address both false and true value.

Author: vfdff

llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp

@@ -509,28 +509,38 @@ static bool simplifySeqSelectWithSameCond(SelectInst &SI,
   if (isa<Constant>(CondVal))
     return false;
 
-  Type *CondType = CondVal->getType();
-  SelectInst *SINext = &SI;
-  Type *SelType = SINext->getType();
-  Value *FalseVal = SINext->getFalseValue();
-  Value *CondNext;
-  while (match(FalseVal, m_Select(m_Value(CondNext), m_Value(), m_Value()))) {
-    // If the type of select is not an integer type or if the condition and
-    // the selection type are not both scalar nor both vector types, there is no
-    // point in attempting to match these patterns.
-    if (CondNext == CondVal && SelType->isIntOrIntVectorTy() &&
-        CondType->isVectorTy() == SelType->isVectorTy())
-      if (Value *S = simplifyWithOpReplaced(FalseVal, CondVal,
-                                            ConstantInt::getFalse(CondType), SQ,
-                                            /* AllowRefinement */ true)) {
-        IC.replaceOperand(*SINext, 2, S);
-        return true;
-      }
+  auto TrysimplifySeqSelect = [=, &SI, &IC](unsigned OpIndex) {
+    assert((OpIndex == 1 || OpIndex == 2) && "Unexpected operand index");
+    Type *CondType = CondVal->getType();
+    Value *RepOp = OpIndex == 1 ? ConstantInt::getTrue(CondType)
+                                : ConstantInt::getFalse(CondType);
+    SelectInst *SINext = &SI;
+    Type *SelType = SINext->getType();
+    Value *ValOp = SINext->getOperand(OpIndex);
+    Value *CondNext;
+    while (match(ValOp, m_Select(m_Value(CondNext), m_Value(), m_Value()))) {
+      if (CondNext == CondVal && SelType->isIntOrIntVectorTy() &&
+          CondType->isVectorTy() == SelType->isVectorTy())
+        if (Value *S = simplifyWithOpReplaced(ValOp, CondVal, RepOp, SQ,
+                                              /* AllowRefinement */ true)) {
+          IC.replaceOperand(*SINext, OpIndex, S);
+          return true;
+        }
 
-    SINext = cast<SelectInst>(FalseVal);
-    SelType = SINext->getType();
-    FalseVal = SINext->getFalseValue();
-  }
+      SINext = cast<SelectInst>(ValOp);
+      SelType = SINext->getType();
+      ValOp = SINext->getOperand(OpIndex);
+    }
+    return false;
+  };
+
+  // Try to simplify the true value of select.
+  if (TrysimplifySeqSelect(1))
+    return true;
+
+  // Try to simplify the false value of select.
+  if (TrysimplifySeqSelect(2))
+    return true;
 
   return false;
 }

llvm/test/Transforms/InstCombine/select.ll

@@ -3724,9 +3724,8 @@ define i32 @sequence_select_with_same_cond_flase (i1 %c1, i1 %c2){
 ; https://alive2.llvm.org/ce/z/HHF-VD
 define i32 @sequence_select_with_same_cond_true (i1 %c1, i1 %c2){
 ; CHECK-LABEL: @sequence_select_with_same_cond_true(
-; CHECK-NEXT:    [[S1:%.*]] = select i1 [[C1:%.*]], i32 45, i32 23
-; CHECK-NEXT:    [[S2:%.*]] = select i1 [[C2:%.*]], i32 [[S1]], i32 666
-; CHECK-NEXT:    [[S3:%.*]] = select i1 [[C1]], i32 [[S2]], i32 789
+; CHECK-NEXT:    [[S2:%.*]] = select i1 [[C2:%.*]], i32 45, i32 666
+; CHECK-NEXT:    [[S3:%.*]] = select i1 [[C1:%.*]], i32 [[S2]], i32 789
 ; CHECK-NEXT:    ret i32 [[S3]]
 ;
   %s1 = select i1 %c1, i32 45, i32 23