diff options
Diffstat (limited to 'gcc/flow.c')
| -rw-r--r-- | gcc/flow.c | 40 |
1 files changed, 40 insertions, 0 deletions
diff --git a/gcc/flow.c b/gcc/flow.c index 32693e41d71..4fd65dca569 100644 --- a/gcc/flow.c +++ b/gcc/flow.c @@ -317,6 +317,7 @@ static void notice_stack_pointer_modification_1 PARAMS ((rtx, rtx, void *)); static void notice_stack_pointer_modification PARAMS ((rtx)); static void mark_reg PARAMS ((rtx, void *)); static void mark_regs_live_at_end PARAMS ((regset)); +static int set_phi_alternative_reg PARAMS ((rtx, int, int, void *)); static void calculate_global_regs_live PARAMS ((sbitmap, sbitmap, int)); static void propagate_block PARAMS ((basic_block, regset, regset, int)); @@ -2486,6 +2487,15 @@ life_analysis (f, nregs, file, remove_dead_code) #endif int flags; sbitmap all_blocks; + + /* Dead code elimination changes basic block structure and therefore + breaks the SSA phi representation. Particularly, a phi node + can have an alternative value for each incoming block, referenced + by the block number. Removing dead code can bump entire blocks + and therefore cause blocks to be renumbered, invalidating the + numbering of phi alternatives. */ + if (remove_dead_code && in_ssa_form) + abort (); /* Record which registers will be eliminated. We use this in mark_used_regs. */ @@ -2960,6 +2970,22 @@ mark_regs_live_at_end (set) diddle_return_value (mark_reg, set); } +/* Callback function for for_each_successor_phi. DATA is a regset. + Sets the SRC_REGNO, the regno of the phi alternative for phi node + INSN, in the regset. */ + +static int +set_phi_alternative_reg (insn, dest_regno, src_regno, data) + rtx insn ATTRIBUTE_UNUSED; + int dest_regno ATTRIBUTE_UNUSED; + int src_regno; + void *data; +{ + regset live = (regset) data; + SET_REGNO_REG_SET (live, src_regno); + return 0; +} + /* Propagate global life info around the graph of basic blocks. Begin considering blocks with their corresponding bit set in BLOCKS_IN. BLOCKS_OUT is set for every block that was changed. */ @@ -3020,6 +3046,13 @@ calculate_global_regs_live (blocks_in, blocks_out, flags) IOR_REG_SET (new_live_at_end, sb->global_live_at_start); } + /* Regs used in phi nodes are not included in + global_live_at_start, since they are live only along a + particular edge. Set those regs that are live because of a + phi node alternative corresponding to this particular block. */ + for_each_successor_phi (bb->index, &set_phi_alternative_reg, + new_live_at_end); + if (bb == ENTRY_BLOCK_PTR) { COPY_REG_SET (bb->global_live_at_end, new_live_at_end); @@ -4688,6 +4721,13 @@ mark_used_regs (needed, live, x, flags, insn) break; } + case PHI: + /* We _do_not_ want to scan operands of phi nodes. Operands of + a phi function are evaluated only when control reaches this + block along a particular edge. Therefore, regs that appear + as arguments to phi should not be added to the global live at + start. */ + return; default: break; |