[InstCombine] Improve coverage of foldSelectValueEquivalence for non-constants

There are a few more cases we can easily cover.
   - If f(Y) simplifies to Y
   - If replace X with Y makes X one-use (and make Y non one-use).

These all require that Y is not undef or poison

Author: goldsteinn

llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp

@@ -1300,6 +1300,8 @@ Instruction *InstCombinerImpl::foldSelectValueEquivalence(SelectInst &Sel,
     if (TrueVal == OldOp)
       return nullptr;
 
+    bool NewOpNeverUndef = false;
+
     if (Value *V = simplifyWithOpReplaced(TrueVal, OldOp, NewOp, SQ,
                                           /* AllowRefinement=*/true)) {
       // Need some guarantees about the new simplified op to ensure we don't inf
@@ -1312,11 +1314,52 @@ Instruction *InstCombinerImpl::foldSelectValueEquivalence(SelectInst &Sel,
         return nullptr;
       }
 
-      // If NewOp is a constant and OldOp is not replace iff NewOp doesn't
-      // contain and undef elements.
-      if (match(NewOp, m_ImmConstant()) &&
-          isGuaranteedNotToBeUndef(NewOp, SQ.AC, &Sel, &DT))
+      // We can't do any further replacement if NewOp may be undef/poison.
+      if (!isGuaranteedNotToBeUndefOrPoison(NewOp, SQ.AC, &Sel, &DT))
+        return nullptr;
+
+      // If NewOp is a constant, replace.
+      if (match(NewOp, m_ImmConstant()))
+        return replaceOperand(Sel, Swapped ? 2 : 1, V);
+
+      // If we simplified the TrueArm -> NewOp then replace.
+      // This handles things like `select`/`min`/`max`/`or`/`and`/etc...
+      if (NewOp == V)
         return replaceOperand(Sel, Swapped ? 2 : 1, V);
+
+      NewOpNeverUndef = true;
+    }
+
+    // If we can't simplify, but we will either:
+    //  1) Create a new binop where both ops are NewOp i.e (add x, y) is "worse"
+    //     than (add y, y) in this case, wait until the second call so we don't
+    //     miss a one-use simplification.
+    //  2) Create a new one-use instruction.
+    // proceed.
+    if (TrueVal->hasOneUse() && isa<Instruction>(TrueVal)) {
+      bool BinOpMatch =
+          match(TrueVal, m_c_BinOp(m_Specific(OldOp), m_Specific(NewOp)));
+      bool NewOneUse = isa<Instruction>(OldOp) && OldOp->hasNUses(2) &&
+                       (!isa<Instruction>(NewOp) || !NewOp->hasOneUse());
+      if (BinOpMatch || NewOneUse) {
+        bool Replaced = false;
+        auto *TrueIns = cast<Instruction>(TrueVal);
+        for (unsigned OpIdx = 0; OpIdx < TrueIns->getNumOperands(); ++OpIdx) {
+          if (TrueIns->getOperand(OpIdx) != OldOp)
+            continue;
+          // Need to ensure NewOp is noundef (same reason as above). Wait
+          // until the last moment to do this check as it can be relatively
+          // expensive.
+          if (!NewOpNeverUndef &&
+              !isGuaranteedNotToBeUndefOrPoison(NewOp, SQ.AC, &Sel, &DT))
+            break;
+          NewOpNeverUndef = true;
+          TrueIns->setOperand(OpIdx, NewOp);
+          Replaced = true;
+        }
+        if (Replaced)
+          return replaceOperand(Sel, Swapped ? 2 : 1, TrueIns);
+      }
     }
 
     // Even if TrueVal does not simplify, we can directly replace a use of

llvm/test/Transforms/InstCombine/select-cmp-eq-op-fold.ll

@@ -6,8 +6,7 @@ declare void @use.i8(i8)
 define i8 @replace_with_y_noundef(i8 %x, i8 noundef %y, i8 %z) {
 ; CHECK-LABEL: @replace_with_y_noundef(
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i8 [[X:%.*]], [[Y:%.*]]
-; CHECK-NEXT:    [[AND:%.*]] = and i8 [[X]], [[Y]]
-; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[CMP]], i8 [[AND]], i8 [[Z:%.*]]
+; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[CMP]], i8 [[Y]], i8 [[Z:%.*]]
 ; CHECK-NEXT:    ret i8 [[SEL]]
 ;
   %cmp = icmp eq i8 %x, %y
@@ -20,8 +19,7 @@ define i8 @replace_with_x_noundef(i8 noundef %x, i8 %y, i8 %z) {
 ; CHECK-LABEL: @replace_with_x_noundef(
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp ne i8 [[X:%.*]], [[Y:%.*]]
 ; CHECK-NEXT:    call void @use.i1(i1 [[CMP]])
-; CHECK-NEXT:    [[AND:%.*]] = or i8 [[X]], [[Y]]
-; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[CMP]], i8 [[Z:%.*]], i8 [[AND]]
+; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[CMP]], i8 [[Z:%.*]], i8 [[X]]
 ; CHECK-NEXT:    ret i8 [[SEL]]
 ;
   %cmp = icmp ne i8 %x, %y
@@ -50,7 +48,7 @@ define i8 @replace_with_y_for_new_oneuse(i8 noundef %xx, i8 noundef %y, i8 %z) {
 ; CHECK-LABEL: @replace_with_y_for_new_oneuse(
 ; CHECK-NEXT:    [[X:%.*]] = mul i8 [[XX:%.*]], 13
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i8 [[X]], [[Y:%.*]]
-; CHECK-NEXT:    [[ADD:%.*]] = add nuw i8 [[X]], [[Y]]
+; CHECK-NEXT:    [[ADD:%.*]] = shl nuw i8 [[Y]], 1
 ; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[CMP]], i8 [[ADD]], i8 [[Z:%.*]]
 ; CHECK-NEXT:    ret i8 [[SEL]]
 ;
@@ -65,7 +63,7 @@ define i8 @replace_with_y_for_new_oneuse2(i8 %xx, i8 noundef %y, i8 %z, i8 %q) {
 ; CHECK-LABEL: @replace_with_y_for_new_oneuse2(
 ; CHECK-NEXT:    [[X:%.*]] = mul i8 [[XX:%.*]], 13
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i8 [[X]], [[Y:%.*]]
-; CHECK-NEXT:    [[ADD:%.*]] = add nuw i8 [[X]], [[Q:%.*]]
+; CHECK-NEXT:    [[ADD:%.*]] = add nuw i8 [[Y]], [[Q:%.*]]
 ; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[CMP]], i8 [[ADD]], i8 [[Z:%.*]]
 ; CHECK-NEXT:    ret i8 [[SEL]]
 ;
@@ -81,7 +79,7 @@ define i8 @replace_with_x_for_new_oneuse(i8 noundef %xx, i8 noundef %yy, i8 %z,
 ; CHECK-NEXT:    [[X:%.*]] = mul i8 [[XX:%.*]], 13
 ; CHECK-NEXT:    [[Y:%.*]] = add i8 [[YY:%.*]], [[W:%.*]]
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i8 [[X]], [[Y]]
-; CHECK-NEXT:    [[MUL:%.*]] = mul i8 [[X]], [[Y]]
+; CHECK-NEXT:    [[MUL:%.*]] = mul i8 [[X]], [[X]]
 ; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[CMP]], i8 [[MUL]], i8 [[Z:%.*]]
 ; CHECK-NEXT:    ret i8 [[SEL]]
 ;
@@ -115,7 +113,7 @@ define i8 @replace_with_x_for_simple_binop(i8 noundef %xx, i8 %yy, i8 %z, i8 %w)
 ; CHECK-NEXT:    [[X:%.*]] = mul i8 [[XX:%.*]], 13
 ; CHECK-NEXT:    [[Y:%.*]] = add i8 [[YY:%.*]], [[W:%.*]]
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i8 [[X]], [[Y]]
-; CHECK-NEXT:    [[MUL:%.*]] = mul i8 [[X]], [[Y]]
+; CHECK-NEXT:    [[MUL:%.*]] = mul i8 [[X]], [[X]]
 ; CHECK-NEXT:    call void @use.i8(i8 [[Y]])
 ; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[CMP]], i8 [[MUL]], i8 [[Z:%.*]]
 ; CHECK-NEXT:    ret i8 [[SEL]]
@@ -147,7 +145,7 @@ define i8 @replace_with_none_for_new_oneuse_fail_maybe_undef(i8 %xx, i8 %y, i8 %
 define i8 @replace_with_y_for_simple_binop(i8 %x, i8 noundef %y, i8 %z) {
 ; CHECK-LABEL: @replace_with_y_for_simple_binop(
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i8 [[X:%.*]], [[Y:%.*]]
-; CHECK-NEXT:    [[MUL:%.*]] = mul nsw i8 [[X]], [[Y]]
+; CHECK-NEXT:    [[MUL:%.*]] = mul nsw i8 [[Y]], [[Y]]
 ; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[CMP]], i8 [[MUL]], i8 [[Z:%.*]]
 ; CHECK-NEXT:    ret i8 [[SEL]]
 ;