X86: Use btq for bit tests if the immediate can't be encoded in 32 bits.

Before:
	movabsq	$4294967296, %rax       ## encoding: [0x48,0xb8,0x00,0x00,0x00,0x00,0x01,0x00,0x00,0x00]
	testq	%rax, %rdi              ## encoding: [0x48,0x85,0xf8]
	jne	LBB0_2                  ## encoding: [0x75,A]

After:
	btq	$32, %rdi               ## encoding: [0x48,0x0f,0xba,0xe7,0x20]
	jb	LBB0_2                  ## encoding: [0x72,A]

btq is usually slower than testq because it doesn't fuse with the jump, but here we're better off
saving one register and a giant movabsq.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@145103 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Target/X86/X86ISelLowering.cpp b/lib/Target/X86/X86ISelLowering.cpp
index 7e35fd24a0ba57f2df9ab37616a707043717c83f..213e880d968d97e3499f9ce92873d668ee4c253a 100644 (file)
--- a/lib/Target/X86/X86ISelLowering.cpp
+++ b/lib/Target/X86/X86ISelLowering.cpp
@@ -8543,11 +8543,19 @@ SDValue X86TargetLowering::LowerToBT(SDValue And, ISD::CondCode CC,
       }
   } else if (Op1.getOpcode() == ISD::Constant) {
     ConstantSDNode *AndRHS = cast<ConstantSDNode>(Op1);
+    uint64_t AndRHSVal = AndRHS->getZExtValue();
     SDValue AndLHS = Op0;
-    if (AndRHS->getZExtValue() == 1 && AndLHS.getOpcode() == ISD::SRL) {
+
+    if (AndRHSVal == 1 && AndLHS.getOpcode() == ISD::SRL) {
       LHS = AndLHS.getOperand(0);
       RHS = AndLHS.getOperand(1);
     }
+
+    // Use BT if the immediate can't be encoded in a TEST instruction.
+    if (!isUInt<32>(AndRHSVal) && isPowerOf2_64(AndRHSVal)) {
+      LHS = AndLHS;
+      RHS = DAG.getConstant(Log2_64_Ceil(AndRHSVal), LHS.getValueType());
+    }
   }
 
   if (LHS.getNode()) {

diff --git a/test/CodeGen/X86/btq.ll b/test/CodeGen/X86/btq.ll
new file mode 100644 (file)
index 0000000..9c137a7
--- /dev/null
+++ b/test/CodeGen/X86/btq.ll
@@ -0,0 +1,35 @@
+; RUN: llc < %s -march=x86-64 | FileCheck %s
+
+declare void @bar()
+
+define void @test1(i64 %foo) nounwind {
+  %and = and i64 %foo, 4294967296
+  %tobool = icmp eq i64 %and, 0
+  br i1 %tobool, label %if.end, label %if.then
+
+; CHECK: test1:
+; CHECK: btq $32
+
+if.then:
+  tail call void @bar() nounwind
+  br label %if.end
+
+if.end:
+  ret void
+}
+
+define void @test2(i64 %foo) nounwind {
+  %and = and i64 %foo, 2147483648
+  %tobool = icmp eq i64 %and, 0
+  br i1 %tobool, label %if.end, label %if.then
+
+; CHECK: test2:
+; CHECK: testl $-2147483648
+
+if.then:
+  tail call void @bar() nounwind
+  br label %if.end
+
+if.end:
+  ret void
+}