DAGCombiner: Improve DAGCombiner select normalization

The current code normalizes select(C0, x, select(C1, x, y)) towards
select(C0|C1, x, y) if the targets prefers that form. This patch adds an
additional rule that if the select(C1, x, y) part already exists in the
function then we want to normalize into the other direction because the
effects of reusing the existing value are bigger than transforming into
the target preferred form.

This addresses regressions following r238793, see also:
http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20150727/290272.html

Differential Revision: http://reviews.llvm.org/D11616

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@245350 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index faa9d351e4693ebe5a5161e4c3c50b6511066a80..d2f6354f712051b81632ee9f65c19cd5fbfad67f 100644 (file)
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -4956,36 +4956,46 @@ SDValue DAGCombiner::visitSELECT(SDNode *N) {
     return SDValue(N, 0);  // Don't revisit N.
 
   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);
+    // The code in this block deals with the following 2 equivalences:
+    //    select(C0|C1, x, y) <=> select(C0, x, select(C1, x, y))
+    //    select(C0&C1, x, y) <=> select(C0, select(C1, x, y), y)
+    // The target can specify its prefered form with the
+    // shouldNormalizeToSelectSequence() callback. However we always transform
+    // to the right anyway if we find the inner select exists in the DAG anyway
+    // and we always transform to the left side if we know that we can further
+    // optimize the combination of the conditions.
+    bool normalizeToSequence
+      = 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);
+      if (normalizeToSequence || !InnerSelect.use_empty())
         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);
+    }
+    // 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);
+      if (normalizeToSequence || !InnerSelect.use_empty())
         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) {
+    if (N1->getOpcode() == ISD::SELECT && N1->hasOneUse()) {
       SDValue N1_0 = N1->getOperand(0);
       SDValue N1_1 = N1->getOperand(1);
       SDValue N1_2 = N1->getOperand(2);
       if (N1_2 == N2 && N0.getValueType() == N1_0.getValueType()) {
         // Create the actual and node if we can generate good code for it.
-        if (!TLI.shouldNormalizeToSelectSequence(*DAG.getContext(), VT)) {
+        if (!normalizeToSequence) {
           SDValue And = DAG.getNode(ISD::AND, SDLoc(N), N0.getValueType(),
                                     N0, N1_0);
           return DAG.getNode(ISD::SELECT, SDLoc(N), N1.getValueType(), And,
@@ -4998,13 +5008,13 @@ SDValue DAGCombiner::visitSELECT(SDNode *N) {
       }
     }
     // select Cond0, X, (select Cond1, X, Y) -> select (or Cond0, Cond1), X, Y
-    if (N2->getOpcode() == ISD::SELECT) {
+    if (N2->getOpcode() == ISD::SELECT && N2->hasOneUse()) {
       SDValue N2_0 = N2->getOperand(0);
       SDValue N2_1 = N2->getOperand(1);
       SDValue N2_2 = N2->getOperand(2);
       if (N2_1 == N1 && N0.getValueType() == N2_0.getValueType()) {
         // Create the actual or node if we can generate good code for it.
-        if (!TLI.shouldNormalizeToSelectSequence(*DAG.getContext(), VT)) {
+        if (!normalizeToSequence) {
           SDValue Or = DAG.getNode(ISD::OR, SDLoc(N), N0.getValueType(),
                                    N0, N2_0);
           return DAG.getNode(ISD::SELECT, SDLoc(N), N1.getValueType(), Or,

diff --git a/test/CodeGen/AArch64/dag-combine-select.ll b/test/CodeGen/AArch64/dag-combine-select.ll
index 01934e91a71f02e44ba18c2a1dfcc0d6a5afbb7b..95204e77f8c2cc91ae5c7674412a789eab2d3d53 100644 (file)
--- a/test/CodeGen/AArch64/dag-combine-select.ll
+++ b/test/CodeGen/AArch64/dag-combine-select.ll
@@ -1,6 +1,8 @@
 ; RUN: llc -o - %s | FileCheck %s
 target triple = "arm64--"
 
+@out = internal global i32 0, align 4
+
 ; Ensure that we transform select(C0, x, select(C1, x, y)) towards
 ; select(C0 | C1, x, y) so we can use CMP;CCMP for the implementation.
 ; CHECK-LABEL: test0:
@@ -15,3 +17,31 @@ define i32 @test0(i32 %v0, i32 %v1, i32 %v2) {
   %sel1 = select i1 %cmp2, i32 %v1, i32 %sel0
   ret i32 %sel1
 }
+
+; Usually we keep select(C0 | C1, x, y) as is on aarch64 to create CMP;CCMP
+; sequences. This case should be transformed to select(C0, select(C1, x, y), y)
+; anyway to get CSE effects.
+; CHECK-LABEL: test1:
+; CHECK-NOT: ccmp
+; CHECK: cmp w0, #7
+; CHECK: adrp x[[OUTNUM:[0-9]+]], out
+; CHECK: csel w[[SEL0NUM:[0-9]+]], w1, w2, eq
+; CHECK: cmp w[[SEL0NUM]], #13
+; CHECK: csel w[[SEL1NUM:[0-9]+]], w1, w2, lo
+; CHECK: cmp w0, #42
+; CHECK: csel w[[SEL2NUM:[0-9]+]], w1, w[[SEL1NUM]], eq
+; CHECK: str w[[SEL1NUM]], [x[[OUTNUM]], :lo12:out]
+; CHECK: str w[[SEL2NUM]], [x[[OUTNUM]], :lo12:out]
+; CHECK: ret
+define void @test1(i32 %bitset, i32 %val0, i32 %val1) {
+  %cmp1 = icmp eq i32 %bitset, 7
+  %cond = select i1 %cmp1, i32 %val0, i32 %val1
+  %cmp5 = icmp ult i32 %cond, 13
+  %cond11 = select i1 %cmp5, i32 %val0, i32 %val1
+  %cmp3 = icmp eq i32 %bitset, 42
+  %or.cond = or i1 %cmp3, %cmp5
+  %cond17 = select i1 %or.cond, i32 %val0, i32 %val1
+  store volatile i32 %cond11, i32* @out, align 4
+  store volatile i32 %cond17, i32* @out, align 4
+  ret void
+}