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Introduce and use x86 JECXZ instruction to reduce cases of testing fo…
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…r null and then branching (generate a single instruction instead). Rewrite checkcast and instanceof to use for their null tests. This saves 2bytes per instruction and improves throughput by 50% (at the cost of extra latency).
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Ian Rogers committed May 26, 2009
1 parent dc32152 commit 887b09c
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Showing 2 changed files with 39 additions and 41 deletions.
19 changes: 19 additions & 0 deletions rvm/src-generated/ia32-assembler/Assembler.in
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Original file line number Diff line number Diff line change
Expand Up @@ -1022,6 +1022,25 @@ public abstract class Assembler extends AbstractAssembler implements RegisterCon
return r;
}

/**
* Generate a forward JECXZ instruction into the generated code.
* This form is used when the compiler wants to hang onto the
* forward reference object and call resolve on it directly. These
* forward references are not handled by the mechanism in the
* assembler; the client is responsible for calling resolve on the
* reference when generating the target instruction. The baseline
* compiler uses this form for jumps within the machine code for a
* single bytecode.
*/
public final ForwardReference forwardJECXZ () {
int miStart = mi;
ForwardReference r = new ForwardReference.ShortBranch(mi);
setMachineCodes(mi++, (byte)0xE3);
mi += 1; // leave space for displacement
if (lister != null) lister.I(miStart, "JECXZ", 0);
return r;
}

/**
* The set of outstanding forward references. This list is used by
* the assembler to keep track of all outstanding forward
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61 changes: 20 additions & 41 deletions rvm/src/org/jikesrvm/compilers/baseline/ia32/BaselineCompilerImpl.java
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Original file line number Diff line number Diff line change
Expand Up @@ -3331,15 +3331,13 @@ protected final void emit_checkcast_resolvedInterface(RVMClass type) {
int interfaceMask = type.getDoesImplementBitMask();

if (VM.BuildFor32Addr) {
asm.emitMOV_Reg_RegInd(S0, SP); // load object from stack into S0
asm.emitTEST_Reg_Reg(S0, S0); // test for null
asm.emitMOV_Reg_RegInd(ECX, SP); // load object from stack into ECX
} else {
asm.emitMOV_Reg_RegInd_Quad(S0, SP); // load object from stack into S0
asm.emitTEST_Reg_Reg_Quad(S0, S0); // test for null
asm.emitMOV_Reg_RegInd_Quad(ECX, SP); // load object from stack into RCX
}
ForwardReference isNull = asm.forwardJcc(Assembler.EQ);
ForwardReference isNull = asm.forwardJECXZ(); // forward branch if ECX == 0

baselineEmitLoadTIB(asm, S0, S0); // S0 = TIB of object
baselineEmitLoadTIB(asm, S0, ECX); // S0 = TIB of object
// S0 = implements bit vector
if (VM.BuildFor32Addr) {
asm.emitMOV_Reg_RegDisp(S0, S0, Offset.fromIntZeroExtend(TIB_DOES_IMPLEMENT_INDEX << LG_WORDSIZE));
Expand Down Expand Up @@ -3379,15 +3377,13 @@ protected final void emit_checkcast_resolvedClass(RVMClass type) {
int LHSId = type.getId();

if (VM.BuildFor32Addr) {
asm.emitMOV_Reg_RegInd(S0, SP); // load object from stack
asm.emitTEST_Reg_Reg(S0, S0); // test for null
asm.emitMOV_Reg_RegInd(ECX, SP); // load object from stack
} else {
asm.emitMOV_Reg_RegInd_Quad(S0, SP); // load object from stack
asm.emitTEST_Reg_Reg_Quad(S0, S0); // test for null
asm.emitMOV_Reg_RegInd_Quad(ECX, SP); // load object from stack
}
ForwardReference isNull = asm.forwardJcc(Assembler.EQ);
ForwardReference isNull = asm.forwardJECXZ(); // jump forward if ECX == 0

baselineEmitLoadTIB(asm, S0, S0); // S0 = TIB of object
baselineEmitLoadTIB(asm, S0, ECX); // S0 = TIB of object
// S0 = superclass IDs
if (VM.BuildFor32Addr) {
asm.emitMOV_Reg_RegDisp(S0, S0, Offset.fromIntZeroExtend(TIB_SUPERCLASS_IDS_INDEX << LG_WORDSIZE));
Expand Down Expand Up @@ -3424,15 +3420,13 @@ protected final void emit_checkcast_resolvedClass(RVMClass type) {
@Override
protected final void emit_checkcast_final(RVMType type) {
if (VM.BuildFor32Addr) {
asm.emitMOV_Reg_RegInd(S0, SP); // load object from stack
asm.emitTEST_Reg_Reg(S0, S0); // test for null
asm.emitMOV_Reg_RegInd(ECX, SP); // load object from stack
} else {
asm.emitMOV_Reg_RegInd_Quad(S0, SP); // load object from stack
asm.emitTEST_Reg_Reg_Quad(S0, S0); // test for null
asm.emitMOV_Reg_RegInd_Quad(ECX, SP); // load object from stack
}
ForwardReference isNull = asm.forwardJcc(Assembler.EQ);
ForwardReference isNull = asm.forwardJECXZ(); // jump forward if ECX == 0

baselineEmitLoadTIB(asm, S0, S0); // TIB of object
baselineEmitLoadTIB(asm, S0, ECX); // TIB of object
if (VM.BuildFor32Addr) {
asm.emitCMP_Reg_Abs(S0, Magic.getTocPointer().plus(type.getTibOffset()));
} else {
Expand Down Expand Up @@ -3466,15 +3460,10 @@ protected final void emit_instanceof_resolvedInterface(RVMClass type) {
int interfaceIndex = type.getDoesImplementIndex();
int interfaceMask = type.getDoesImplementBitMask();

asm.emitPOP_Reg(S0); // load object from stack
if (VM.BuildFor32Addr) {
asm.emitTEST_Reg_Reg(S0, S0); // test for null
} else {
asm.emitTEST_Reg_Reg_Quad(S0, S0); // test for null
}
ForwardReference isNull = asm.forwardJcc(Assembler.EQ);
asm.emitPOP_Reg(ECX); // load object from stack
ForwardReference isNull = asm.forwardJECXZ(); // test for null

baselineEmitLoadTIB(asm, S0, S0); // S0 = TIB of object
baselineEmitLoadTIB(asm, S0, ECX); // S0 = TIB of object
// S0 = implements bit vector
if (VM.BuildFor32Addr) {
asm.emitMOV_Reg_RegDisp(S0, S0, Offset.fromIntZeroExtend(TIB_DOES_IMPLEMENT_INDEX << LG_WORDSIZE));
Expand Down Expand Up @@ -3516,16 +3505,11 @@ protected final void emit_instanceof_resolvedClass(RVMClass type) {
int LHSDepth = type.getTypeDepth();
int LHSId = type.getId();

asm.emitPOP_Reg(S0); // load object from stack
if (VM.BuildFor32Addr) {
asm.emitTEST_Reg_Reg(S0, S0); // test for null
} else {
asm.emitTEST_Reg_Reg_Quad(S0, S0); // test for null
}
ForwardReference isNull = asm.forwardJcc(Assembler.EQ);
asm.emitPOP_Reg(ECX); // load object from stack
ForwardReference isNull = asm.forwardJECXZ(); // test for null

// get superclass display from object's TIB
baselineEmitLoadTIB(asm, S0, S0);
baselineEmitLoadTIB(asm, S0, ECX);
if (VM.BuildFor32Addr) {
asm.emitMOV_Reg_RegDisp(S0, S0, Offset.fromIntZeroExtend(TIB_SUPERCLASS_IDS_INDEX << LG_WORDSIZE));
} else {
Expand Down Expand Up @@ -3565,15 +3549,10 @@ protected final void emit_instanceof_resolvedClass(RVMClass type) {
@Override
protected final void emit_instanceof_final(RVMType type) {
asm.emitPOP_Reg(S0); // load object from stack
if (VM.BuildFor32Addr) {
asm.emitTEST_Reg_Reg(S0, S0); // test for null
} else {
asm.emitTEST_Reg_Reg_Quad(S0, S0); // test for null
}
ForwardReference isNull = asm.forwardJcc(Assembler.EQ);
ForwardReference isNull = asm.forwardJECXZ(); // test for null

// compare TIB of object to desired TIB and push true if equal
baselineEmitLoadTIB(asm, S0, S0);
baselineEmitLoadTIB(asm, S0, ECX);
if (VM.BuildFor32Addr) {
asm.emitCMP_Reg_Abs(S0, Magic.getTocPointer().plus(type.getTibOffset()));
} else {
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