From 898d11e86468564d796ec87457ca060320ff46a1 Mon Sep 17 00:00:00 2001
From: Matthias Braun <matze@braunis.de>
Date: Fri, 6 Mar 2015 19:49:10 +0000
Subject: DAGCombiner: Canonicalize select(and/or,x,y) depending on target.

This is based on the following equivalences:
select(C0 & C1, X, Y) <=> select(C0, select(C1, X, Y), Y)
select(C0 | C1, X, Y) <=> select(C0, X, select(C1, X, Y))

Many target cannot perform and/or on the CPU flags and therefore the
right side should be choosen to avoid materializign the i1 flags in an
integer register. If the target can perform this operation efficiently
we normalize to the left form.

Differential Revision: http://reviews.llvm.org/D7622

llvm-svn: 231507
---
 llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp | 63 +++++++++++++++++++++++++++
 1 file changed, 63 insertions(+)

(limited to 'llvm/lib/CodeGen/SelectionDAG')

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index e247961a7ba..64228a1aa9b 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -4819,6 +4819,69 @@ SDValue DAGCombiner::visitSELECT(SDNode *N) {
     return SimplifySelect(SDLoc(N), N0, N1, N2);
   }
 
+  if (VT0 == MVT::i1) {
+    if (TLI.shouldNormalizeToSelectSequence(*DAG.getContext(), VT)) {
+      // select (and Cond0, Cond1), X, Y
+      //   -> select Cond0, (select Cond1, X, Y), Y
+      if (N0->getOpcode() == ISD::AND && N0->hasOneUse()) {
+        SDValue Cond0 = N0->getOperand(0);
+        SDValue Cond1 = N0->getOperand(1);
+        SDValue InnerSelect = DAG.getNode(ISD::SELECT, SDLoc(N),
+                                          N1.getValueType(), Cond1, N1, N2);
+        return DAG.getNode(ISD::SELECT, SDLoc(N), N1.getValueType(), Cond0,
+                           InnerSelect, N2);
+      }
+      // select (or Cond0, Cond1), X, Y -> select Cond0, X, (select Cond1, X, Y)
+      if (N0->getOpcode() == ISD::OR && N0->hasOneUse()) {
+        SDValue Cond0 = N0->getOperand(0);
+        SDValue Cond1 = N0->getOperand(1);
+        SDValue InnerSelect = DAG.getNode(ISD::SELECT, SDLoc(N),
+                                          N1.getValueType(), Cond1, N1, N2);
+        return DAG.getNode(ISD::SELECT, SDLoc(N), N1.getValueType(), Cond0, N1,
+                           InnerSelect);
+      }
+    }
+
+    // select Cond0, (select Cond1, X, Y), Y -> select (and Cond0, Cond1), X, Y
+    if (N1->getOpcode() == ISD::SELECT) {
+      SDValue N1_0 = N1->getOperand(0);
+      SDValue N1_1 = N1->getOperand(1);
+      SDValue N1_2 = N1->getOperand(2);
+      if (N1_2 == N2) {
+        // Create the actual and node if we can generate good code for it.
+        if (!TLI.shouldNormalizeToSelectSequence(*DAG.getContext(), VT)) {
+          SDValue And = DAG.getNode(ISD::AND, SDLoc(N), N0.getValueType(),
+                                    N0, N1_0);
+          return DAG.getNode(ISD::SELECT, SDLoc(N), N1.getValueType(), And,
+                             N1_1, N2);
+        }
+        // Otherwise see if we can optimize the "and" to a better pattern.
+        if (SDValue Combined = visitANDLike(N0, N1_0, N))
+          return DAG.getNode(ISD::SELECT, SDLoc(N), N1.getValueType(), Combined,
+                             N1_1, N2);
+      }
+    }
+    // select Cond0, X, (select Cond1, X, Y) -> select (or Cond0, Cond1), X, Y
+    if (N2->getOpcode() == ISD::SELECT) {
+      SDValue N2_0 = N2->getOperand(0);
+      SDValue N2_1 = N2->getOperand(1);
+      SDValue N2_2 = N2->getOperand(2);
+      if (N2_1 == N1) {
+        // Create the actual or node if we can generate good code for it.
+        if (!TLI.shouldNormalizeToSelectSequence(*DAG.getContext(), VT)) {
+          SDValue Or = DAG.getNode(ISD::OR, SDLoc(N), N0.getValueType(),
+                                   N0, N2_0);
+          return DAG.getNode(ISD::SELECT, SDLoc(N), N1.getValueType(), Or,
+                             N1, N2_2);
+        }
+        // Otherwise see if we can optimize to a better pattern.
+        if (SDValue Combined = visitORLike(N0, N2_0, N))
+          return DAG.getNode(ISD::SELECT, SDLoc(N), N1.getValueType(), Combined,
+                             N1, N2_2);
+      }
+    }
+  }
+
   return SDValue();
 }
 
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