fwprop.c (forward_propagate_subreg): Skip the SIGN/ZERO_EXTEND optimization if the source register is already extended.
gcc/ * fwprop.c (forward_propagate_subreg): Skip the SIGN/ZERO_EXTEND optimization if the source register is already extended. From-SVN: r182504
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@ -1,3 +1,8 @@
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2011-12-19 Richard Sandiford <rdsandiford@googlemail.com>
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* fwprop.c (forward_propagate_subreg): Skip the SIGN/ZERO_EXTEND
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optimization if the source register is already extended.
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2011-12-19 Richard Sandiford <rdsandiford@googlemail.com>
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* lower-subreg.c (can_decompose_p): Check every word of a hard
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15
gcc/fwprop.c
15
gcc/fwprop.c
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@ -1112,7 +1112,18 @@ forward_propagate_subreg (df_ref use, rtx def_insn, rtx def_set)
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/* If this is a SUBREG of a ZERO_EXTEND or SIGN_EXTEND, and the SUBREG
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is the low part of the reg being extended then just use the inner
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operand. Don't do this if the ZERO_EXTEND or SIGN_EXTEND insn will
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be removed due to it matching a LOAD_EXTEND_OP load from memory. */
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be removed due to it matching a LOAD_EXTEND_OP load from memory,
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or due to the operation being a no-op when applied to registers.
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For example, if we have:
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A: (set (reg:DI X) (sign_extend:DI (reg:SI Y)))
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B: (... (subreg:SI (reg:DI X)) ...)
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and mode_rep_extended says that Y is already sign-extended,
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the backend will typically allow A to be combined with the
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definition of Y or, failing that, allow A to be deleted after
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reload through register tying. Introducing more uses of Y
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prevents both optimisations. */
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else if (subreg_lowpart_p (use_reg))
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{
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use_insn = DF_REF_INSN (use);
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@ -1123,6 +1134,8 @@ forward_propagate_subreg (df_ref use, rtx def_insn, rtx def_set)
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&& REGNO (XEXP (src, 0)) >= FIRST_PSEUDO_REGISTER
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&& GET_MODE (XEXP (src, 0)) == use_mode
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&& !free_load_extend (src, def_insn)
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&& (targetm.mode_rep_extended (use_mode, GET_MODE (src))
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!= (int) GET_CODE (src))
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&& all_uses_available_at (def_insn, use_insn))
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return try_fwprop_subst (use, DF_REF_LOC (use), XEXP (src, 0),
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def_insn, false);
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