linux-kernel - [RFC PATCH v2 3/6] KVM: emulate: cleanup decode

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Date:	Thu, 10 Apr 2014 20:03:29 -0400
From:	Bandan Das <bsd@...hat.com>
To:	kvm@...r.kernel.org
Cc:	Marcelo Tosatti <mtosatti@...hat.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Gleb Natapov <gleb@...nel.org>, linux-kernel@...r.kernel.org
Subject: [RFC PATCH v2 3/6] KVM: emulate: cleanup decode_rm

Remove the if conditional - that will help us avoid
an "else initialize to 0" Also, rearrange operators
for slightly better code.

Signed-off-by: Bandan Das <bsd@...hat.com>
---
 arch/x86/kvm/emulate.c | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index a6d9892..9cbaba2 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -1064,19 +1064,17 @@ static int decode_modrm(struct x86_emulate_ctxt *ctxt,
 			struct operand *op)
 {
 	u8 sib;
-	int index_reg = 0, base_reg = 0, scale;
+	int index_reg, base_reg, scale;
 	int rc = X86EMUL_CONTINUE;
 	ulong modrm_ea = 0;
 
-	if (ctxt->rex_prefix) {
-		ctxt->modrm_reg = (ctxt->rex_prefix & 4) << 1;	/* REX.R */
-		index_reg = (ctxt->rex_prefix & 2) << 2; /* REX.X */
-		ctxt->modrm_rm = base_reg = (ctxt->rex_prefix & 1) << 3; /* REG.B */
-	}
+	index_reg = (ctxt->rex_prefix << 2) & 8; /* REX.X */
+	base_reg = (ctxt->rex_prefix << 3) & 8; /* REG.B */
 
-	ctxt->modrm_mod |= (ctxt->modrm & 0xc0) >> 6;
-	ctxt->modrm_reg |= (ctxt->modrm & 0x38) >> 3;
-	ctxt->modrm_rm |= (ctxt->modrm & 0x07);
+	ctxt->modrm_mod = (ctxt->modrm & 0xc0) >> 6;
+	ctxt->modrm_reg = ((ctxt->rex_prefix << 1) & 8) | /* REX.R */
+		((ctxt->modrm & 0x38) >> 3);
+	ctxt->modrm_rm = base_reg | (ctxt->modrm & 0x07);
 	ctxt->modrm_seg = VCPU_SREG_DS;
 
 	if (ctxt->modrm_mod == 3) {
-- 
1.8.3.1

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