--- -----------------------------------------------------------------------------
--- Boring Cmm traversals for collecting usage info and substitutions.
-
-getStmtUses :: CmmStmt -> UniqFM Int
-getStmtUses (CmmAssign _ e) = getExprUses e
-getStmtUses (CmmStore e1 e2) = plusUFM_C (+) (getExprUses e1) (getExprUses e2)
-getStmtUses (CmmCall target _ es)
- = plusUFM_C (+) (uses target) (getExprsUses (map fst es))
- where uses (CmmForeignCall e _) = getExprUses e
- uses _ = emptyUFM
-getStmtUses (CmmCondBranch e _) = getExprUses e
-getStmtUses (CmmSwitch e _) = getExprUses e
-getStmtUses (CmmJump e _) = getExprUses e
-getStmtUses _ = emptyUFM
-
-getExprUses :: CmmExpr -> UniqFM Int
-getExprUses (CmmReg (CmmLocal (LocalReg u _))) = unitUFM u 1
-getExprUses (CmmRegOff (CmmLocal (LocalReg u _)) _) = unitUFM u 1
-getExprUses (CmmLoad e _) = getExprUses e
-getExprUses (CmmMachOp _ es) = getExprsUses es
-getExprUses _other = emptyUFM
-
-getExprsUses es = foldr (plusUFM_C (+)) emptyUFM (map getExprUses es)
+ -- We can skip over assignments to other tempoararies, because we
+ -- know that expressions aren't side-effecting and temporaries are
+ -- single-assignment.
+ ok_to_skip = case stmt of
+ CmmNop -> True
+ CmmComment{} -> True
+ CmmAssign (CmmLocal (LocalReg u' _)) rhs | u' /= u -> True
+ CmmAssign g@(CmmGlobal _) rhs -> not (g `regUsedIn` expr)
+ _other -> False
+