[dev.ssa] cmd/compile: use 32-bit load to read writebarrier
Avoid targeting a partial register with load;
ensure source of load (writebarrier) is aligned.
Better yet would be "CMPB $1,writebarrier" but that requires
wrestling with flagalloc (mem operand complicates moving
instruction around).
Didn't see a change in time for
benchcmd -n 10 Build go build net/http
Verified that we clean the code up properly:
0x20a8 <main.main+104>: mov 0xc30a2(%rip),%eax
# 0xc5150 <runtime.writeBarrier>
0x20ae <main.main+110>: test %al,%al
Change-Id: Id5fb8c260eaec27bd727cb0ae1476c60343b0986
Reviewed-on: https://go-review.googlesource.com/19998 Reviewed-by: Keith Randall <khr@golang.org>