Commit d70fc3c1 authored by Edward Z. Yang's avatar Edward Z. Yang

CmmOpt cannot assume single assignment for hand-written or new codegen Cmm.

This change may constitute a substantial performance hit, due to the new
creation of a set for every instruction we emit.
Signed-off-by: Edward Z. Yang's avatarEdward Z. Yang <ezyang@mit.edu>
parent 12929a21
......@@ -115,12 +115,15 @@ cmmMiniInlineStmts uses (stmt@(CmmAssign (CmmLocal (LocalReg u _)) expr) : stmts
cmmMiniInlineStmts uses (stmt:stmts)
= stmt : cmmMiniInlineStmts uses stmts
lookForInline u expr (stmt : rest)
lookForInline u expr stmts = lookForInline' u expr regset stmts
where regset = foldRegsUsed extendRegSet emptyRegSet expr
lookForInline' u expr regset (stmt : rest)
| Just 1 <- lookupUFM (countUses stmt) u, ok_to_inline
= Just (inlineStmt u expr stmt : rest)
| ok_to_skip
= case lookForInline u expr rest of
= case lookForInline' u expr regset rest of
Nothing -> Nothing
Just stmts -> Just (stmt:stmts)
......@@ -137,13 +140,18 @@ lookForInline u expr (stmt : rest)
CmmCall{} -> hasNoGlobalRegs expr
_ -> True
-- We can skip over assignments to other tempoararies, because we
-- know that expressions aren't side-effecting and temporaries are
-- single-assignment.
-- Expressions aren't side-effecting. Temporaries may or may not
-- be single-assignment depending on the source (the old code
-- generator creates single-assignment code, but hand-written Cmm
-- and Cmm from the new code generator is not single-assignment.)
-- So we do an extra check to make sure that the register being
-- changed is not one we were relying on. I don't know how much of a
-- performance hit this is (we have to create a regset for every
-- instruction.) -- EZY
ok_to_skip = case stmt of
CmmNop -> True
CmmComment{} -> True
CmmAssign (CmmLocal (LocalReg u' _)) rhs | u' /= u -> True
CmmAssign (CmmLocal r@(LocalReg u' _)) rhs | u' /= u && not (r `elemRegSet` regset) -> True
CmmAssign g@(CmmGlobal _) rhs -> not (g `regUsedIn` expr)
_other -> False
......
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