[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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@313774 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index 0d14f62b3e9d95cebbbea748aaa8ad01ba672047..bcd60bca177bb97e18e416443abb57d363b83f8a 100644 (file)
--- a/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/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/lib/Transforms/InstCombine/InstCombineInternal.h b/lib/Transforms/InstCombine/InstCombineInternal.h
index 5f110dac26b9676667aae31ff52e3e706db363e1..22edcfa044415fac7b341f0b2908b3af86dbfca7 100644 (file)
--- a/lib/Transforms/InstCombine/InstCombineInternal.h
+++ b/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/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index c99f757dfef9329643c92bbe47b590e25562ddec..0f762710fdeedcc1030d209c07fa63c6c2985a5f 100644 (file)
--- a/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/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/lib/Transforms/InstCombine/InstructionCombining.cpp b/lib/Transforms/InstCombine/InstructionCombining.cpp
index 8f2b44036f66e645577df8da68825908afe544c9..f51b838144555b280b6a82201b676e9ba886e5f7 100644 (file)
--- a/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/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

diff --git a/test/Transforms/InstCombine/select_arithmetic.ll b/test/Transforms/InstCombine/select_arithmetic.ll
new file mode 100644 (file)
index 0000000..d33bbdd
--- /dev/null
+++ b/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
+}
+