[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

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);

llvm/lib/Transforms/InstCombine/InstCombineInternal.h

@@ -600,6 +600,11 @@ class LLVM_LIBRARY_VISIBILITY InstCombiner
   /// 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 *,

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).

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

llvm/test/Transforms/InstCombine/select_arithmetic.ll

@@ -0,0 +1,40 @@
+; RUN: opt < %s -instcombine -S | FileCheck %s
+
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+
+; Tests folding constants from two similar selects that feed a add
+define float @test1(i1 zeroext %arg) #0 {
+  %tmp = select i1 %arg, float 5.000000e+00, float 6.000000e+00
+  %tmp1 = select i1 %arg, float 1.000000e+00, float 9.000000e+00
+  %tmp2 = fadd float %tmp, %tmp1
+  ret float %tmp2
+; CHECK-LABEL: @test1(
+; CHECK: %tmp2 = select i1 %arg, float 6.000000e+00, float 1.500000e+01
+; CHECK-NOT: fadd
+; CHECK: ret float %tmp2
+}
+
+; Tests folding constants from two similar selects that feed a sub
+define float @test2(i1 zeroext %arg) #0 {
+  %tmp = select i1 %arg, float 5.000000e+00, float 6.000000e+00
+  %tmp1 = select i1 %arg, float 1.000000e+00, float 9.000000e+00
+  %tmp2 = fsub float %tmp, %tmp1
+  ret float %tmp2
+; CHECK-LABEL: @test2(
+; CHECK: %tmp2 = select i1 %arg, float 4.000000e+00, float -3.000000e+00
+; CHECK-NOT: fsub
+; CHECK: ret float %tmp2
+}
+
+; Tests folding constants from two similar selects that feed a mul
+define float @test3(i1 zeroext %arg) #0 {
+  %tmp = select i1 %arg, float 5.000000e+00, float 6.000000e+00
+  %tmp1 = select i1 %arg, float 1.000000e+00, float 9.000000e+00
+  %tmp2 = fmul float %tmp, %tmp1
+  ret float %tmp2
+; CHECK-LABEL: @test3(
+; CHECK: %tmp2 = select i1 %arg, float 5.000000e+00, float 5.400000e+01
+; CHECK-NOT: fmul
+; CHECK: ret float %tmp2
+}
+