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8211046: Forced data dependencies serve no purpose on x86

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Reviewed-by: eosterlund, rehn
This commit is contained in:
David Holmes 2018-10-12 03:51:02 -04:00
parent f4df5cb4c3
commit 55692eb0ca
1 changed files with 2 additions and 27 deletions
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29
src/hotspot/cpu/x86/jniFastGetField_x86_64.cpp
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@ -35,9 +35,6 @@
#define BUFFER_SIZE 30*wordSize
// Instead of issuing lfence for LoadLoad barrier, we create data dependency
// between loads, which is more efficient than lfence.
// Common register usage:
// rax/xmm0: result
// c_rarg0: jni env
@ -77,12 +74,6 @@ address JNI_FastGetField::generate_fast_get_int_field0(BasicType type) {
__ mov (robj, c_rarg1);
__ testb (rcounter, 1);
__ jcc (Assembler::notZero, slow);
__ xorptr(robj, rcounter);
__ xorptr(robj, rcounter); // obj, since
// robj ^ rcounter ^ rcounter == robj
// robj is data dependent on rcounter.
__ mov (roffset, c_rarg2);
__ shrptr(roffset, 2); // offset
@ -103,12 +94,7 @@ address JNI_FastGetField::generate_fast_get_int_field0(BasicType type) {
default: ShouldNotReachHere();
}
// create data dependency on rax
__ lea(rcounter_addr, counter);
__ xorptr(rcounter_addr, rax);
__ xorptr(rcounter_addr, rax);
__ cmpl (rcounter, Address(rcounter_addr, 0));
__ cmp32 (rcounter, counter);
__ jcc (Assembler::notEqual, slow);
__ ret (0);
@ -178,11 +164,6 @@ address JNI_FastGetField::generate_fast_get_float_field0(BasicType type) {
__ testb (rcounter, 1);
__ jcc (Assembler::notZero, slow);
__ xorptr(robj, rcounter);
__ xorptr(robj, rcounter); // obj, since
// robj ^ rcounter ^ rcounter == robj
// robj is data dependent on rcounter.
// Both robj and rtmp are clobbered by try_resolve_jobject_in_native.
BarrierSetAssembler* bs = BarrierSet::barrier_set()->barrier_set_assembler();
bs->try_resolve_jobject_in_native(masm, /* jni_env */ c_rarg0, robj, rtmp, slow);
@ -198,13 +179,7 @@ address JNI_FastGetField::generate_fast_get_float_field0(BasicType type) {
case T_DOUBLE: __ movdbl (xmm0, Address(robj, roffset, Address::times_1)); break;
default: ShouldNotReachHere();
}
__ lea(rcounter_addr, counter);
__ movdq (rax, xmm0);
// counter address is data dependent on xmm0.
__ xorptr(rcounter_addr, rax);
__ xorptr(rcounter_addr, rax);
__ cmpl (rcounter, Address(rcounter_addr, 0));
__ cmp32 (rcounter, counter);
__ jcc (Assembler::notEqual, slow);
__ ret (0);