From 36a398fe701802e6cdd25a6a8e7ff94bed7631d7 Mon Sep 17 00:00:00 2001
From: Owen Anderson <resistor@mac.com>
Date: Thu, 30 Apr 2015 04:06:32 +0000
Subject: [PATCH] Semantically revert r236031, which is not a good idea for
 in-order targets.

At the least it should be guarded by some kind of target hook.
It also introduced catastrophic compile time and code quality
regressions on some out of tree targets (test case still being
reduced/sanitized).

Sanjay agreed with reverting this patch until these issues can be
resolved.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@236199 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/CodeGen/SelectionDAG/DAGCombiner.cpp | 31 -----------------
 test/CodeGen/X86/fp-fast.ll              | 42 ------------------------
 2 files changed, 73 deletions(-)

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 2a9f8e1d304..a5f558fb79c 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -7647,33 +7647,6 @@ SDValue DAGCombiner::visitFSUBForFMACombine(SDNode *N) {
   return SDValue();
 }
 
-static SDValue ReassociateBinops(SDNode *N, SelectionDAG &DAG) {
-  assert(N->getNumOperands() == 2 && "Invalid node for binop reassociation");
-  SDValue N0 = N->getOperand(0);
-  SDValue N1 = N->getOperand(1);
-  EVT VT = N->getValueType(0);
-  SDLoc DL(N);
-  unsigned Opcode = N->getOpcode();
-
-  // Canonicalize chains of this operation to LHS to allow the following fold.
-  if (N0.getOpcode() != Opcode && N1.getOpcode() == Opcode)
-    return DAG.getNode(Opcode, DL, VT, N1, N0);
-  
-  // Convert a chain of 3 dependent operations into 2 independent operations
-  // and 1 dependent operation:
-  //  (op N0: (op N00: (op z, w), N01: y), N1: x) ->
-  //  (op N00: (op z, w), (op N1: x, N01: y))
-  if (N0.getOpcode() == Opcode && N0.hasOneUse() && N1.getOpcode() != Opcode) {
-    SDValue N00 = N0.getOperand(0);
-    if (N00.getOpcode() == Opcode) {
-      SDValue N01 = N0.getOperand(1);
-      SDValue NewOp = DAG.getNode(Opcode, DL, VT, N1, N01);
-      return DAG.getNode(Opcode, DL, VT, N00, NewOp);
-    }
-  }
-  return SDValue();
-}
-
 SDValue DAGCombiner::visitFADD(SDNode *N) {
   SDValue N0 = N->getOperand(0);
   SDValue N1 = N->getOperand(1);
@@ -7808,10 +7781,6 @@ SDValue DAGCombiner::visitFADD(SDNode *N) {
                            N0.getOperand(0), DAG.getConstantFP(4.0, DL, VT));
       }
     }
-    
-    if (SDValue Reassociated = ReassociateBinops(N, DAG))
-      return Reassociated;
-
   } // enable-unsafe-fp-math
 
   // FADD -> FMA combines:
diff --git a/test/CodeGen/X86/fp-fast.ll b/test/CodeGen/X86/fp-fast.ll
index eb2ebd9119a..27af5738ca3 100644
--- a/test/CodeGen/X86/fp-fast.ll
+++ b/test/CodeGen/X86/fp-fast.ll
@@ -114,45 +114,3 @@ define float @test11(float %a) {
   ret float %t2
 }
 
-; Verify that the first two adds are independent; the destination registers
-; are used as source registers for the third add.
-
-define float @reassociate_adds1(float %a, float %b, float %c, float %d) {
-; CHECK-LABEL: reassociate_adds1:
-; CHECK:       # BB#0:
-; CHECK-NEXT:    vaddss %xmm1, %xmm0, %xmm0
-; CHECK-NEXT:    vaddss %xmm2, %xmm3, %xmm1
-; CHECK-NEXT:    vaddss %xmm1, %xmm0, %xmm0
-; CHECK-NEXT:    retq
-  %add0 = fadd float %a, %b
-  %add1 = fadd float %add0, %c
-  %add2 = fadd float %add1, %d
-  ret float %add2
-}
-
-define float @reassociate_adds2(float %a, float %b, float %c, float %d) {
-; CHECK-LABEL: reassociate_adds2:
-; CHECK:       # BB#0:
-; CHECK-NEXT:    vaddss %xmm1, %xmm0, %xmm0
-; CHECK-NEXT:    vaddss %xmm2, %xmm3, %xmm1
-; CHECK-NEXT:    vaddss %xmm1, %xmm0, %xmm0
-; CHECK-NEXT:    retq
-  %add0 = fadd float %a, %b
-  %add1 = fadd float %c, %add0
-  %add2 = fadd float %add1, %d
-  ret float %add2
-}
-
-define float @reassociate_adds3(float %a, float %b, float %c, float %d) {
-; CHECK-LABEL: reassociate_adds3:
-; CHECK:       # BB#0:
-; CHECK-NEXT:    vaddss %xmm1, %xmm0, %xmm0
-; CHECK-NEXT:    vaddss %xmm2, %xmm3, %xmm1
-; CHECK-NEXT:    vaddss %xmm1, %xmm0, %xmm0
-; CHECK-NEXT:    retq
-  %add0 = fadd float %a, %b
-  %add1 = fadd float %add0, %c
-  %add2 = fadd float %d, %add1
-  ret float %add2
-}
-
-- 
2.34.1