JDK-8247979 : aarch64: missing side effect of killing flags for clearArray_reg_reg
- Type: Bug
- Component: hotspot
- Sub-Component: compiler
- Affected Version: 11,15,16
- Priority: P4
- Status: Resolved
- Resolution: Fixed
- OS: generic
- CPU: aarch64
- Submitted: 2020-06-22
- Updated: 2024-11-13
- Resolved: 2020-06-23
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| JDK 11 | JDK 16 | Other |
|---|---|---|
| 11.0.11-oracleFixed | 16 b03Fixed  |
openjdk8u292Fixed |
Related Reports
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Relates :
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Description
In clearArray_reg_reg, we call function: MacroAssembler::zero words(Register ptr, Register cnt).
This function modifies the flags register by doing a cmp instruction at entry. But this is not reflected in the side effect of clearArray_reg_reg.
We didn't see this is triggers problems. But this may pose similar risk as bug: 8224828: aarch64: rflags is not correct after safepoint poll.
Fix is trivial:
diff -r 2342d5af52b7 src/hotspot/cpu/aarch64/aarch64.ad
--- a/src/hotspot/cpu/aarch64/aarch64.ad Mon Jun 22 08:09:23 2020 +0200
+++ b/src/hotspot/cpu/aarch64/aarch64.ad Mon Jun 22 15:58:05 2020 +0800
@@ -13845,7 +13845,7 @@
instruct clearArray_reg_reg(iRegL_R11 cnt, iRegP_R10 base, Universe dummy, rFlagsReg cr)
%{
match(Set dummy (ClearArray cnt base));
- effect(USE_KILL cnt, USE_KILL base);
+ effect(USE_KILL cnt, USE_KILL base, KILL cr);
ins_cost(4 * INSN_COST);
format %{ "ClearArray $cnt, $base" %}
BTW: clearArray_imm_reg does not have the issue since it calls a different function: MacroAssembler::zero_words(Register base, u_int64_t cnt)
13843 // clearing of an array
13844
13845 instruct clearArray_reg_reg(iRegL_R11 cnt, iRegP_R10 base, Universe dummy, rFlagsReg cr)
13846 %{
13847 match(Set dummy (ClearArray cnt base));
13848 effect(USE_KILL cnt, USE_KILL base);
13849
13850 ins_cost(4 * INSN_COST);
13851 format %{ "ClearArray $cnt, $base" %}
13852
13853 ins_encode %{
13854 __ zero_words($base$$Register, $cnt$$Register);
13855 %}
13856
13857 ins_pipe(pipe_class_memory);
13858 %}
4771 void MacroAssembler::zero_words(Register ptr, Register cnt)
4772 {
4773 assert(is_power_of_2(zero_words_block_size), "adjust this");
4774 assert(ptr == r10 && cnt == r11, "mismatch in register usage");
4775
4776 BLOCK_COMMENT("zero_words {");
4777 cmp(cnt, (u1)zero_words_block_size); <=================
Comments
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