[InstCombine] Add select simplifications

In these cases, two selects have constant selectable operands for
both the true and false components and have the same conditional
expression.
We then create two arithmetic operations of the same type and feed a
final select operation using the result of the true arithmetic for the true
operand and the result of the false arithmetic for the false operand and reuse
the original conditionl expression.
The arithmetic operations are naturally folded as a consequence, leaving
only the newly formed select to replace the old arithmetic operation.

Patch by: Michael Berg <michael_c_berg@apple.com>
Differential Revision: https://reviews.llvm.org/D37019

llvm-svn: 313774

4 files changed, 44 insertions, 52 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index 0d14f62b3e9..bcd60bca177 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1387,30 +1387,9 @@ Instruction *InstCombiner::visitFAdd(BinaryOperator &I) {
     }
   }
 
-  // select C, 0, B + select C, A, 0 -> select C, A, B
-  {
-    Value *A1, *B1, *C1, *A2, *B2, *C2;
-    if (match(LHS, m_Select(m_Value(C1), m_Value(A1), m_Value(B1))) &&
-        match(RHS, m_Select(m_Value(C2), m_Value(A2), m_Value(B2)))) {
-      if (C1 == C2) {
-        Constant *Z1=nullptr, *Z2=nullptr;
-        Value *A, *B, *C=C1;
-        if (match(A1, m_AnyZero()) && match(B2, m_AnyZero())) {
-            Z1 = dyn_cast<Constant>(A1); A = A2;
-            Z2 = dyn_cast<Constant>(B2); B = B1;
-        } else if (match(B1, m_AnyZero()) && match(A2, m_AnyZero())) {
-            Z1 = dyn_cast<Constant>(B1); B = B2;
-            Z2 = dyn_cast<Constant>(A2); A = A1;
-        }
-
-        if (Z1 && Z2 &&
-            (I.hasNoSignedZeros() ||
-             (Z1->isNegativeZeroValue() && Z2->isNegativeZeroValue()))) {
-          return SelectInst::Create(C, A, B);
-        }
-      }
-    }
-  }
+  // Handle specials cases for FAdd with selects feeding the operation
+  if (Value *V = SimplifySelectsFeedingBinaryOp(I, LHS, RHS))
+    return replaceInstUsesWith(I, V);
 
   if (I.hasUnsafeAlgebra()) {
     if (Value *V = FAddCombine(Builder).simplify(&I))
@@ -1760,6 +1739,10 @@ Instruction *InstCombiner::visitFSub(BinaryOperator &I) {
     }
   }
 
+  // Handle specials cases for FSub with selects feeding the operation
+  if (Value *V = SimplifySelectsFeedingBinaryOp(I, Op0, Op1))
+    return replaceInstUsesWith(I, V);
+
   if (I.hasUnsafeAlgebra()) {
     if (Value *V = FAddCombine(Builder).simplify(&I))
       return replaceInstUsesWith(I, V);
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
index 5f110dac26b..22edcfa0444 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
+++ b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
@@ -600,6 +600,11 @@ private:
   /// value, or null if it didn't simplify.
   Value *SimplifyUsingDistributiveLaws(BinaryOperator &I);
 
+  // Binary Op helper for select operations where the expression can be
+  // efficiently reorganized.
+  Value *SimplifySelectsFeedingBinaryOp(BinaryOperator &I, Value *LHS,
+                                        Value *RHS);
+
   /// This tries to simplify binary operations by factorizing out common terms
   /// (e. g. "(A*B)+(A*C)" -> "A*(B+C)").
   Value *tryFactorization(BinaryOperator &, Instruction::BinaryOps, Value *,
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index c99f757dfef..0f762710fde 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -736,6 +736,10 @@ Instruction *InstCombiner::visitFMul(BinaryOperator &I) {
       }
     }
 
+    // Handle specials cases for FMul with selects feeding the operation
+    if (Value *V = SimplifySelectsFeedingBinaryOp(I, Op0, Op1))
+      return replaceInstUsesWith(I, V);
+
     // (X*Y) * X => (X*X) * Y where Y != X
     //  The purpose is two-fold:
     //   1) to form a power expression (of X).
diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index 8f2b44036f6..f51b8381445 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -719,36 +719,36 @@ Value *InstCombiner::SimplifyUsingDistributiveLaws(BinaryOperator &I) {
     }
   }
 
-  // (op (select (a, c, b)), (select (a, d, b))) -> (select (a, (op c, d), 0))
-  // (op (select (a, b, c)), (select (a, b, d))) -> (select (a, 0, (op c, d)))
-  if (auto *SI0 = dyn_cast<SelectInst>(LHS)) {
-    if (auto *SI1 = dyn_cast<SelectInst>(RHS)) {
-      if (SI0->getCondition() == SI1->getCondition()) {
-        Value *SI = nullptr;
-        if (Value *V =
-                SimplifyBinOp(TopLevelOpcode, SI0->getFalseValue(),
-                              SI1->getFalseValue(), SQ.getWithInstruction(&I)))
-          SI = Builder.CreateSelect(SI0->getCondition(),
-                                    Builder.CreateBinOp(TopLevelOpcode,
-                                                        SI0->getTrueValue(),
-                                                        SI1->getTrueValue()),
-                                    V);
-        if (Value *V =
-                SimplifyBinOp(TopLevelOpcode, SI0->getTrueValue(),
-                              SI1->getTrueValue(), SQ.getWithInstruction(&I)))
-          SI = Builder.CreateSelect(
-              SI0->getCondition(), V,
-              Builder.CreateBinOp(TopLevelOpcode, SI0->getFalseValue(),
-                                  SI1->getFalseValue()));
-        if (SI) {
-          SI->takeName(&I);
-          return SI;
-        }
-      }
-    }
+  return SimplifySelectsFeedingBinaryOp(I, LHS, RHS);
+}
+
+Value *InstCombiner::SimplifySelectsFeedingBinaryOp(BinaryOperator &I,
+                                                    Value *LHS, Value *RHS) {
+  Instruction::BinaryOps Opcode = I.getOpcode();
+  // (op (select (a, b, c)), (select (a, d, e))) -> (select (a, (op b, d), (op
+  // c, e)))
+  Value *A, *B, *C, *D, *E;
+  Value *SI = nullptr;
+  if (match(LHS, m_Select(m_Value(A), m_Value(B), m_Value(C))) &&
+      match(RHS, m_Select(m_Specific(A), m_Value(D), m_Value(E)))) {
+    BuilderTy::FastMathFlagGuard Guard(Builder);
+    if (isa<FPMathOperator>(&I))
+      Builder.setFastMathFlags(I.getFastMathFlags());
+
+    Value *V1 = SimplifyBinOp(Opcode, C, E, SQ.getWithInstruction(&I));
+    Value *V2 = SimplifyBinOp(Opcode, B, D, SQ.getWithInstruction(&I));
+    if (V1 && V2)
+      SI = Builder.CreateSelect(A, V2, V1);
+    else if (V2)
+      SI = Builder.CreateSelect(A, V2, Builder.CreateBinOp(Opcode, C, E));
+    else if (V1)
+      SI = Builder.CreateSelect(A, Builder.CreateBinOp(Opcode, B, D), V1);
+
+    if (SI)
+      SI->takeName(&I);
   }
 
-  return nullptr;
+  return SI;
 }
 
 /// Given a 'sub' instruction, return the RHS of the instruction if the LHS is a