Request for reviews (M): 6747051: Improve code and implicit null check generation for compressed oops
Vladimir.Kozlov at Sun.COM
Thu Sep 11 11:34:41 PDT 2008
Fixed 6747051: Improve code and implicit null check generation for compressed oops
Currently C2 often generates redundant tests against null with compressed oops:
testl R10, R10 # compressed ptr
jeq B75 P=0.000001 C=-1.000000
movl RDX, [R11 + #12] # range
decode_heap_oop also contains a test of R10 that's not exposed to the optimizer.
Push DecodeN node below the test to the non-null path to use
decode_heap_oop_not_null mach node which does not have 0 test.
Keep CastPP node for such cases and replace CastPP(DecodeN) with DecodeN
clone node with NotNull type during final_graph_reshape phase.
This will also allow to generate more implicit null checks with compressed oops.
On x86_64 the resulting code will be:
movl RDX, [R12 + R10 << 3 + #12] (compressed oop addressing) # range
And on sparc (requires to pin DecodeN to the non-null path):
decode_heap_oop_not_null R_L7, R_O1
LDUW [R_O1 + #12],R_L2 ! range
Also don't compare memory address types in Matcher when DecodeN is
consumed by an address expression since types will be different
at least by nullness.
Fix verified (y/n): y, generated code.
JPRT, refworkload, specjbb2005, specjvm2008
More information about the hotspot-compiler-dev