diff options
Diffstat (limited to 'src/cmd/compile/internal/ssa/deadstore.go')
| -rw-r--r-- | src/cmd/compile/internal/ssa/deadstore.go | 16 |
1 files changed, 7 insertions, 9 deletions
diff --git a/src/cmd/compile/internal/ssa/deadstore.go b/src/cmd/compile/internal/ssa/deadstore.go index 69616b3a88..1cbba02f2f 100644 --- a/src/cmd/compile/internal/ssa/deadstore.go +++ b/src/cmd/compile/internal/ssa/deadstore.go @@ -73,9 +73,11 @@ func dse(f *Func) { } // Walk backwards looking for dead stores. Keep track of shadowed addresses. - // An "address" is an SSA Value which encodes both the address and size of - // the write. This code will not remove dead stores to the same address - // of different types. + // A "shadowed address" is a pointer and a size describing a memory region that + // is known to be written. We keep track of shadowed addresses in the shadowed + // map, mapping the ID of the address to the size of the shadowed region. + // Since we're walking backwards, writes to a shadowed region are useless, + // as they will be immediately overwritten. shadowed.clear() v := last @@ -93,17 +95,13 @@ func dse(f *Func) { sz = v.AuxInt } if shadowedSize := int64(shadowed.get(v.Args[0].ID)); shadowedSize != -1 && shadowedSize >= sz { - // Modify store into a copy + // Modify the store/zero into a copy of the memory state, + // effectively eliding the store operation. if v.Op == OpStore { // store addr value mem v.SetArgs1(v.Args[2]) } else { // zero addr mem - typesz := v.Args[0].Type.Elem().Size() - if sz != typesz { - f.Fatalf("mismatched zero/store sizes: %d and %d [%s]", - sz, typesz, v.LongString()) - } v.SetArgs1(v.Args[1]) } v.Aux = nil |