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

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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
This commit is contained in:
Benjamin Kramer 2011-11-23 13:54:17 +00:00
parent e4513b1fc5
commit f238f50aaf
2 changed files with 44 additions and 1 deletions
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10
lib/Target/X86/X86ISelLowering.cpp
View File

@ -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()) {

35
test/CodeGen/X86/btq.ll Normal file
View File

@ -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
}