1. Hoist minus sign as high as possible in an attempt to reveal

   some optimization opportunities (in the enclosing supper-expressions).

   rule 1. (-0.0 - X ) * Y => -0.0 - (X * Y)
     if expression "-0.0 - X" has only one reference.

   rule 2. (0.0 - X ) * Y => -0.0 - (X * Y)
     if expression "0.0 - X" has only one reference, and
        the instruction is marked "noSignedZero".

2. Eliminate negation (The compiler was already able to handle these
    opt if the 0.0s are replaced with -0.0.)

   rule 3: (0.0 - X) * (0.0 - Y) => X * Y
   rule 4: (0.0 - X) * C => X * -C
   if the expr is flagged "noSignedZero".

3. 
  Rule 5: (X*Y) * X => (X*X) * Y
   if X!=Y and the expression is flagged with "UnsafeAlgebra".

   The purpose of this transformation is two-fold:
    a) to form a power expression (of X).
    b) potentially shorten the critical path: After transformation, the
       latency of the instruction Y is amortized by the expression of X*X,
       and therefore Y is in a "less critical" position compared to what it
      was before the transformation. 

4. Remove the InstCombine code about simplifiying "X * select".
   
   The reasons are following:
    a) The "select" is somewhat architecture-dependent, therefore the
       higher level optimizers are not able to precisely predict if
       the simplification really yields any performance improvement
       or not.

    b) The "select" operator is bit complicate, and tends to obscure
       optimization opportunities. It is btter to keep it as low as
       possible in expr tree, and let CodeGen to tackle the optimization.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@172551 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 60 insertions, 31 deletions

diff --git a/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index 29846c1..8e4267f 100644
--- a/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -377,6 +377,8 @@ Instruction *InstCombiner::visitFMul(BinaryOperator &I) {
   if (Value *V = SimplifyFMulInst(Op0, Op1, I.getFastMathFlags(), TD))
     return ReplaceInstUsesWith(I, V);
 
+  bool AllowReassociate = I.hasUnsafeAlgebra();
+
   // Simplify mul instructions with a constant RHS.
   if (isa<Constant>(Op1)) {
     // Try to fold constant mul into select arguments.
@@ -389,7 +391,7 @@ Instruction *InstCombiner::visitFMul(BinaryOperator &I) {
         return NV;
 
     ConstantFP *C = dyn_cast<ConstantFP>(Op1);
-    if (C && I.hasUnsafeAlgebra() && C->getValueAPF().isNormal()) {
+    if (C && AllowReassociate && C->getValueAPF().isNormal()) {
       // Let MDC denote an expression in one of these forms:
       // X * C, C/X, X/C, where C is a constant.
       //
@@ -430,7 +432,7 @@ Instruction *InstCombiner::visitFMul(BinaryOperator &I) {
                         BinaryOperator::CreateFAdd(M0, M1) :
                         BinaryOperator::CreateFSub(M0, M1);
             Instruction *RI = cast<Instruction>(R);
-            RI->setHasUnsafeAlgebra(true);
+            RI->copyFastMathFlags(&I);
             return RI;
           }
         }
@@ -438,9 +440,6 @@ Instruction *InstCombiner::visitFMul(BinaryOperator &I) {
     }
   }
 
-  if (Value *Op0v = dyn_castFNegVal(Op0))     // -X * -Y = X*Y
-    if (Value *Op1v = dyn_castFNegVal(Op1))
-      return BinaryOperator::CreateFMul(Op0v, Op1v);
 
   // Under unsafe algebra do:
   // X * log2(0.5*Y) = X*log2(Y) - X
@@ -469,36 +468,66 @@ Instruction *InstCombiner::visitFMul(BinaryOperator &I) {
     }
   }
 
-  // X * cond ? 1.0 : 0.0 => cond ? X : 0.0
-  if (I.hasNoNaNs() && I.hasNoSignedZeros()) {
-    Value *V0 = I.getOperand(0);
-    Value *V1 = I.getOperand(1);
-    Value *Cond, *SLHS, *SRHS;
-    bool Match = false;
-
-    if (match(V0, m_Select(m_Value(Cond), m_Value(SLHS), m_Value(SRHS)))) {
-      Match = true;
-    } else if (match(V1, m_Select(m_Value(Cond), m_Value(SLHS), 
-                     m_Value(SRHS)))) {
-      Match = true;
-      std::swap(V0, V1);
+  // Handle symmetric situation in a 2-iteration loop
+  Value *Opnd0 = Op0;
+  Value *Opnd1 = Op1;
+  for (int i = 0; i < 2; i++) {
+    bool IgnoreZeroSign = I.hasNoSignedZeros();
+    if (BinaryOperator::isFNeg(Opnd0, IgnoreZeroSign)) {
+      Value *N0 = dyn_castFNegVal(Opnd0, IgnoreZeroSign);
+      Value *N1 = dyn_castFNegVal(Opnd1, IgnoreZeroSign);
+
+      // -X * -Y => X*Y
+      if (N1)
+        return BinaryOperator::CreateFMul(N0, N1);
+
+      if (Opnd0->hasOneUse()) {
+        // -X * Y => -(X*Y) (Promote negation as high as possible)
+        Value *T = Builder->CreateFMul(N0, Opnd1);
+        cast<Instruction>(T)->setDebugLoc(I.getDebugLoc());
+        Instruction *Neg = BinaryOperator::CreateFNeg(T);
+        if (I.getFastMathFlags().any()) {
+          cast<Instruction>(T)->copyFastMathFlags(&I);
+          Neg->copyFastMathFlags(&I);
+        }
+        return Neg;
+      }
     }
 
-    if (Match) {
-      ConstantFP *C0 = dyn_cast<ConstantFP>(SLHS);
-      ConstantFP *C1 = dyn_cast<ConstantFP>(SRHS);
-
-      if (C0 && C1 &&
-          ((C0->isZero() && C1->isExactlyValue(1.0)) ||
-           (C1->isZero() && C0->isExactlyValue(1.0)))) {
-        Value *T;
-        if (C0->isZero())
-          T = Builder->CreateSelect(Cond, SLHS, V1);
-        else
-          T = Builder->CreateSelect(Cond, V1, SRHS);
-        return ReplaceInstUsesWith(I, T);
+    // (X*Y) * X => (X*X) * Y where Y != X
+    //  The purpose is two-fold: 
+    //   1) to form a power expression (of X).
+    //   2) potentially shorten the critical path: After transformation, the
+    //  latency of the instruction Y is amortized by the expression of X*X,
+    //  and therefore Y is in a "less critical" position compared to what it
+    //  was before the transformation.
+    //
+    if (AllowReassociate) {
+      Value *Opnd0_0, *Opnd0_1;
+      if (Opnd0->hasOneUse() &&
+          match(Opnd0, m_FMul(m_Value(Opnd0_0), m_Value(Opnd0_1)))) {
+        Value *Y = 0;
+        if (Opnd0_0 == Opnd1 && Opnd0_1 != Opnd1)
+          Y = Opnd0_1;
+        else if (Opnd0_1 == Opnd1 && Opnd0_0 != Opnd1)
+          Y = Opnd0_0;
+
+        if (Y) {
+          Instruction *T = cast<Instruction>(Builder->CreateFMul(Opnd1, Opnd1));
+          T->copyFastMathFlags(&I);
+          T->setDebugLoc(I.getDebugLoc());
+
+          Instruction *R = BinaryOperator::CreateFMul(T, Y);
+          R->copyFastMathFlags(&I);
+          return R;
+        }
       }
     }
+
+    if (!isa<Constant>(Op1))
+      std::swap(Opnd0, Opnd1);
+    else
+      break;
   }
 
   return Changed ? &I : 0;