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108 lines
6.0 KiB
XML
108 lines
6.0 KiB
XML
<?xml version="1.0" encoding="utf-8"?>
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<?xml-stylesheet type="text/xsl" encoding="UTF-8" href="iform.xsl" version="1.0"?>
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<!DOCTYPE instructionsection PUBLIC "-//ARM//DTD instructionsection //EN" "iform-p.dtd">
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<!-- Copyright (c) 2010-2022 Arm Limited or its affiliates. All rights reserved. -->
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<!-- This document is Non-Confidential. This document may only be used and distributed in accordance with the terms of the agreement entered into by Arm and the party that Arm delivered this document to. -->
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<instructionsection id="BC_cond" title="BC.cond -- A64" type="instruction">
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<docvars>
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<docvar key="branch-offset" value="br19" />
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<docvar key="compare-with" value="cmp-cond" />
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<docvar key="instr-class" value="general" />
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<docvar key="isa" value="A64" />
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<docvar key="mnemonic" value="BC" />
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</docvars>
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<heading>BC.cond</heading>
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<desc>
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<brief>
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<para>Branch Consistent conditionally</para>
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</brief>
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<authored>
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<para>Branch Consistent conditionally to a label at a PC-relative offset, with a hint that this branch will behave very consistently and is very unlikely to change direction.</para>
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</authored>
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</desc>
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<alias_list howmany="0"></alias_list>
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<classes>
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<iclass name="19-bit signed PC-relative branch offset" oneof="1" id="iclass_br19" no_encodings="1" isa="A64">
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<docvars>
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<docvar key="branch-offset" value="br19" />
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<docvar key="compare-with" value="cmp-cond" />
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<docvar key="instr-class" value="general" />
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<docvar key="isa" value="A64" />
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<docvar key="mnemonic" value="BC" />
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</docvars>
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<iclassintro count="1"></iclassintro>
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<arch_variants>
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<arch_variant name="ARMv8.8" feature="FEAT_HBC" />
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</arch_variants>
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<regdiagram form="32" psname="aarch64/instrs/branch/conditional/hinted">
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<box hibit="31" width="7" settings="7">
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<c>0</c>
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<c>1</c>
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<c>0</c>
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<c>1</c>
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<c>0</c>
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<c>1</c>
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<c>0</c>
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</box>
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<box hibit="24" name="o1" settings="1">
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<c>0</c>
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</box>
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<box hibit="23" width="19" name="imm19" usename="1">
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<c colspan="19"></c>
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</box>
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<box hibit="4" name="o0" settings="1">
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<c>1</c>
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</box>
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<box hibit="3" width="4" name="cond" usename="1">
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<c colspan="4"></c>
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</box>
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</regdiagram>
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<encoding name="BC_only_condbranch" oneofinclass="1" oneof="1" label="">
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<docvars>
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<docvar key="branch-offset" value="br19" />
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<docvar key="compare-with" value="cmp-cond" />
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<docvar key="instr-class" value="general" />
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<docvar key="isa" value="A64" />
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<docvar key="mnemonic" value="BC" />
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</docvars>
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<asmtemplate><text>BC.</text><a link="sa_cond" hover="Standard condition (field "cond")"><cond></a><text> </text><a link="sa_label" hover="Label to be conditionally branched to (field imm19)"><label></a></asmtemplate>
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</encoding>
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<ps_section howmany="1">
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<ps name="aarch64/instrs/branch/conditional/hinted" mylink="aarch64.instrs.branch.conditional.hinted" enclabels="" sections="1" secttype="noheading">
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<pstext mayhavelinks="1" section="Decode" rep_section="decode">if !<a link="impl-shared.HaveFeatHBC.0" file="shared_pseudocode.xml" hover="function: boolean HaveFeatHBC()">HaveFeatHBC</a>() then UNDEFINED;
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bits(64) offset = <a link="impl-shared.SignExtend.2" file="shared_pseudocode.xml" hover="function: bits(N) SignExtend(bits(M) x, integer N)">SignExtend</a>(imm19:'00', 64);
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bits(4) condition = cond;</pstext>
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</ps>
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</ps_section>
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</iclass>
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</classes>
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<explanations scope="all">
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<explanation enclist="BC_only_condbranch" symboldefcount="1">
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<symbol link="sa_cond"><cond></symbol>
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<account encodedin="cond">
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<intro>
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<para>Is one of the standard conditions, encoded in the "cond" field in the standard way.</para>
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</intro>
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</account>
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</explanation>
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<explanation enclist="BC_only_condbranch" symboldefcount="1">
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<symbol link="sa_label"><label></symbol>
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<account encodedin="imm19">
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<intro>
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<para>Is the program label to be conditionally branched to. Its offset from the address of this instruction, in the range +/-1MB, is encoded as "imm19" times 4.</para>
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</intro>
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</account>
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</explanation>
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</explanations>
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<ps_section howmany="1">
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<ps name="aarch64/instrs/branch/conditional/hinted" mylink="execute" enclabels="" sections="1" secttype="Operation">
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<pstext mayhavelinks="1" section="Execute" rep_section="execute">boolean branch_conditional = TRUE;
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if <a link="impl-shared.ConditionHolds.1" file="shared_pseudocode.xml" hover="function: boolean ConditionHolds(bits(4) cond)">ConditionHolds</a>(condition) then
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<a link="impl-shared.BranchTo.3" file="shared_pseudocode.xml" hover="function: BranchTo(bits(N) target, BranchType branch_type, boolean branch_conditional)">BranchTo</a>(<a link="impl-aarch64.PC.read.0" file="shared_pseudocode.xml" hover="accessor: bits(64) PC[]">PC</a>[] + offset, <a link="BranchType_DIR" file="shared_pseudocode.xml" hover="enumeration BranchType { BranchType_DIRCALL, BranchType_INDCALL, BranchType_ERET, BranchType_DBGEXIT, BranchType_RET, BranchType_DIR, BranchType_INDIR, BranchType_EXCEPTION, BranchType_TMFAIL, BranchType_RESET, BranchType_UNKNOWN}">BranchType_DIR</a>, branch_conditional);
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else
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<a link="impl-shared.BranchNotTaken.2" file="shared_pseudocode.xml" hover="function: BranchNotTaken(BranchType branchtype, boolean branch_conditional)">BranchNotTaken</a>(<a link="BranchType_DIR" file="shared_pseudocode.xml" hover="enumeration BranchType { BranchType_DIRCALL, BranchType_INDCALL, BranchType_ERET, BranchType_DBGEXIT, BranchType_RET, BranchType_DIR, BranchType_INDIR, BranchType_EXCEPTION, BranchType_TMFAIL, BranchType_RESET, BranchType_UNKNOWN}">BranchType_DIR</a>, branch_conditional);</pstext>
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</ps>
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</ps_section>
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</instructionsection>
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