From 1c81ad149de69dd1c53146a3587b536f279d2a58 Mon Sep 17 00:00:00 2001
From: Matthias Braun <matze@braunis.de>
Date: Tue, 18 Aug 2015 20:48:29 +0000
Subject: [PATCH] DAGCombiner: Optimize SELECTs first before turning them into
 SELECT_CC

This is part of http://reviews.llvm.org/D11616 - I just decided to split
this up into a separate commit.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@245349 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/CodeGen/SelectionDAG/DAGCombiner.cpp   | 64 +++++++++++-----------
 test/CodeGen/AArch64/dag-combine-select.ll | 17 ++++++
 2 files changed, 49 insertions(+), 32 deletions(-)
 create mode 100644 test/CodeGen/AArch64/dag-combine-select.ll

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 585cff0de0b..faa9d351e46 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -4955,38 +4955,6 @@ SDValue DAGCombiner::visitSELECT(SDNode *N) {
   if (SimplifySelectOps(N, N1, N2))
     return SDValue(N, 0);  // Don't revisit N.
 
-  // fold selects based on a setcc into other things, such as min/max/abs
-  if (N0.getOpcode() == ISD::SETCC) {
-    // select x, y (fcmp lt x, y) -> fminnum x, y
-    // select x, y (fcmp gt x, y) -> fmaxnum x, y
-    //
-    // This is OK if we don't care about what happens if either operand is a
-    // NaN.
-    //
-
-    // FIXME: Instead of testing for UnsafeFPMath, this should be checking for
-    // no signed zeros as well as no nans.
-    const TargetOptions &Options = DAG.getTarget().Options;
-    if (Options.UnsafeFPMath &&
-        VT.isFloatingPoint() && N0.hasOneUse() &&
-        DAG.isKnownNeverNaN(N1) && DAG.isKnownNeverNaN(N2)) {
-      ISD::CondCode CC = cast<CondCodeSDNode>(N0.getOperand(2))->get();
-
-      if (SDValue FMinMax = combineMinNumMaxNum(SDLoc(N), VT, N0.getOperand(0),
-                                                N0.getOperand(1), N1, N2, CC,
-                                                TLI, DAG))
-        return FMinMax;
-    }
-
-    if ((!LegalOperations &&
-         TLI.isOperationLegalOrCustom(ISD::SELECT_CC, VT)) ||
-        TLI.isOperationLegal(ISD::SELECT_CC, VT))
-      return DAG.getNode(ISD::SELECT_CC, SDLoc(N), VT,
-                         N0.getOperand(0), N0.getOperand(1),
-                         N1, N2, N0.getOperand(2));
-    return SimplifySelect(SDLoc(N), N0, N1, N2);
-  }
-
   if (VT0 == MVT::i1) {
     if (TLI.shouldNormalizeToSelectSequence(*DAG.getContext(), VT)) {
       // select (and Cond0, Cond1), X, Y
@@ -5050,6 +5018,38 @@ SDValue DAGCombiner::visitSELECT(SDNode *N) {
     }
   }
 
+  // fold selects based on a setcc into other things, such as min/max/abs
+  if (N0.getOpcode() == ISD::SETCC) {
+    // select x, y (fcmp lt x, y) -> fminnum x, y
+    // select x, y (fcmp gt x, y) -> fmaxnum x, y
+    //
+    // This is OK if we don't care about what happens if either operand is a
+    // NaN.
+    //
+
+    // FIXME: Instead of testing for UnsafeFPMath, this should be checking for
+    // no signed zeros as well as no nans.
+    const TargetOptions &Options = DAG.getTarget().Options;
+    if (Options.UnsafeFPMath &&
+        VT.isFloatingPoint() && N0.hasOneUse() &&
+        DAG.isKnownNeverNaN(N1) && DAG.isKnownNeverNaN(N2)) {
+      ISD::CondCode CC = cast<CondCodeSDNode>(N0.getOperand(2))->get();
+
+      if (SDValue FMinMax = combineMinNumMaxNum(SDLoc(N), VT, N0.getOperand(0),
+                                                N0.getOperand(1), N1, N2, CC,
+                                                TLI, DAG))
+        return FMinMax;
+    }
+
+    if ((!LegalOperations &&
+         TLI.isOperationLegalOrCustom(ISD::SELECT_CC, VT)) ||
+        TLI.isOperationLegal(ISD::SELECT_CC, VT))
+      return DAG.getNode(ISD::SELECT_CC, SDLoc(N), VT,
+                         N0.getOperand(0), N0.getOperand(1),
+                         N1, N2, N0.getOperand(2));
+    return SimplifySelect(SDLoc(N), N0, N1, N2);
+  }
+
   return SDValue();
 }
 
diff --git a/test/CodeGen/AArch64/dag-combine-select.ll b/test/CodeGen/AArch64/dag-combine-select.ll
new file mode 100644
index 00000000000..01934e91a71
--- /dev/null
+++ b/test/CodeGen/AArch64/dag-combine-select.ll
@@ -0,0 +1,17 @@
+; RUN: llc -o - %s | FileCheck %s
+target triple = "arm64--"
+
+; 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:
+; CHECK: cmp w0, #7
+; CHECK: ccmp w1, #0, #0, ne
+; CHECK: csel w0, w1, w2, gt
+; CHECK: ret
+define i32 @test0(i32 %v0, i32 %v1, i32 %v2) {
+  %cmp1 = icmp eq i32 %v0, 7
+  %cmp2 = icmp sgt i32 %v1, 0
+  %sel0 = select i1 %cmp1, i32 %v1, i32 %v2
+  %sel1 = select i1 %cmp2, i32 %v1, i32 %sel0
+  ret i32 %sel1
+}
-- 
2.34.1