[PATCH] D18910: [x86] use BMI 'andn' for logic + compare ops

[Sanjay Patel via llvm-commits]

spatel created this revision.
spatel added reviewers: ab, RKSimon, kbsmith1.
spatel added a subscriber: llvm-commits.
Herald added a subscriber: mcrosier.

With BMI, we can use 'andn' to save an instruction when the result is only used in a compare.
This is related to one of the potential sequences to check 'isfinite' in:
https://llvm.org/bugs/show_bug.cgi?id=27164

http://reviews.llvm.org/D18910

Files:
  include/llvm/CodeGen/SelectionDAGNodes.h
  lib/CodeGen/SelectionDAG/SelectionDAG.cpp
  lib/Target/X86/X86ISelLowering.cpp
  test/CodeGen/X86/bmi.ll

Index: test/CodeGen/X86/bmi.ll
===================================================================
--- test/CodeGen/X86/bmi.ll
+++ test/CodeGen/X86/bmi.ll
@@ -136,12 +136,11 @@
   ret i64 %tmp2
 }
 
-; FIXME: Don't choose a 'test' if an 'andn' can be used.
+; Don't choose a 'test' if an 'andn' can be used.
 define i1 @andn_cmp(i32 %x, i32 %y) {
 ; CHECK-LABEL: andn_cmp:
 ; CHECK:       # BB#0:
-; CHECK-NEXT:    notl %edi
-; CHECK-NEXT:    testl %esi, %edi
+; CHECK-NEXT:    andnl %esi, %edi, %eax
 ; CHECK-NEXT:    sete %al
 ; CHECK-NEXT:    retq
 ;
@@ -151,12 +150,11 @@
   ret i1 %cmp
 }
 
-; FIXME: Don't choose a 'test' if an 'andn' can be used.
+; Don't choose a 'test' if an 'andn' can be used.
 define i1 @andn_cmp_swap_ops(i64 %x, i64 %y) {
 ; CHECK-LABEL: andn_cmp_swap_ops:
 ; CHECK:       # BB#0:
-; CHECK-NEXT:    notq %rdi
-; CHECK-NEXT:    testq %rdi, %rsi
+; CHECK-NEXT:    andnq %rsi, %rdi, %rax
 ; CHECK-NEXT:    sete %al
 ; CHECK-NEXT:    retq
 ;
Index: lib/Target/X86/X86ISelLowering.cpp
===================================================================
--- lib/Target/X86/X86ISelLowering.cpp
+++ lib/Target/X86/X86ISelLowering.cpp
@@ -14764,10 +14764,20 @@
     break;
 
   case ISD::AND:
-    // If the primary and result isn't used, don't bother using X86ISD::AND,
+    // If the primary 'and' result isn't used, don't bother using X86ISD::AND,
     // because a TEST instruction will be better.
-    if (!hasNonFlagsUse(Op))
-      break;
+    if (!hasNonFlagsUse(Op)) {
+      SDValue Op0 = ArithOp->getOperand(0);
+      SDValue Op1 = ArithOp->getOperand(1);
+      EVT VT = ArithOp.getValueType();
+      bool isAndn = isBitwiseNot(Op0) || isBitwiseNot(Op1);
+      bool isLegalAndnType = VT == MVT::i32 || VT == MVT::i64;
+
+      // But if we can combine this into an ANDN operation, then create an AND
+      // now and allow it to be pattern matched into an ANDN.
+      if (!(Subtarget.hasBMI() && isAndn && isLegalAndnType))
+        break;
+    }
     // FALL THROUGH
   case ISD::SUB:
   case ISD::OR:
Index: lib/CodeGen/SelectionDAG/SelectionDAG.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -6708,6 +6708,10 @@
   return Const != nullptr && Const->isOne();
 }
 
+bool llvm::isBitwiseNot(SDValue V) {
+  return V.getOpcode() == ISD::XOR && isAllOnesConstant(V.getOperand(1));
+}
+
 HandleSDNode::~HandleSDNode() {
   DropOperands();
 }
Index: include/llvm/CodeGen/SelectionDAGNodes.h
===================================================================
--- include/llvm/CodeGen/SelectionDAGNodes.h
+++ include/llvm/CodeGen/SelectionDAGNodes.h
@@ -1358,6 +1358,9 @@
 bool isAllOnesConstant(SDValue V);
 /// Returns true if \p V is a constant integer one.
 bool isOneConstant(SDValue V);
+/// Returns true if \p V is a bitwise not operation. Assumes that an all ones
+/// constant is canonicalized to be operand 1.
+bool isBitwiseNot(SDValue V);
 
 class GlobalAddressSDNode : public SDNode {
   const GlobalValue *TheGlobal;


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