turn things like:
if (X == 0 || X == 2)
...where the comparisons and branches are in different blocks... into a switch
instruction. This comes up a lot in various programs, and works well with
the switch/switch merging code I checked earlier. For example, this testcase:
int switchtest(int C) {
return C == 0 ? f(123) :
C == 1 ? f(3123) :
C == 4 ? f(312) :
C == 5 ? f(1234): f(444);
}
is converted into this:
switch int %C, label %cond_false.3 [
int 0, label %cond_true.0
int 1, label %cond_true.1
int 4, label %cond_true.2
int 5, label %cond_true.3
]
instead of a whole bunch of conditional branches.
Admittedly the code is ugly, and incomplete. To be complete, we need to add
br -> switch merging and switch -> br merging. For example, this testcase:
struct foo { int Q, R, Z; };
#define A (X->Q+X->R * 123)
int test(struct foo *X) {
return A == 123 ? X1() :
A == 12321 ? X2():
(A == 111 || A == 222) ? X3() :
A == 875 ? X4() : X5();
}
Gets compiled to this:
switch int %tmp.7, label %cond_false.2 [
int 123, label %cond_true.0
int 12321, label %cond_true.1
int 111, label %cond_true.2
int 222, label %cond_true.2
]
...
cond_false.2: ; preds = %entry
%tmp.52 = seteq int %tmp.7, 875 ; <bool> [#uses=1]
br bool %tmp.52, label %cond_true.3, label %cond_false.3
where the branch could be folded into the switch.
This kind of thing occurs *ALL OF THE TIME*, especially in programs like
176.gcc, which is a horrible mess of code. It contains stuff like *shudder*:
#define SWITCH_TAKES_ARG(CHAR) \
( (CHAR) == 'D' \
|| (CHAR) == 'U' \
|| (CHAR) == 'o' \
|| (CHAR) == 'e' \
|| (CHAR) == 'u' \
|| (CHAR) == 'I' \
|| (CHAR) == 'm' \
|| (CHAR) == 'L' \
|| (CHAR) == 'A' \
|| (CHAR) == 'h' \
|| (CHAR) == 'z')
and
#define CONST_OK_FOR_LETTER_P(VALUE, C) \
((C) == 'I' ? SMALL_INTVAL (VALUE) \
: (C) == 'J' ? SMALL_INTVAL (-(VALUE)) \
: (C) == 'K' ? (unsigned)(VALUE) < 32 \
: (C) == 'L' ? ((VALUE) & 0xffff) == 0 \
: (C) == 'M' ? integer_ok_for_set (VALUE) \
: (C) == 'N' ? (VALUE) < 0 \
: (C) == 'O' ? (VALUE) == 0 \
: (C) == 'P' ? (VALUE) >= 0 \
: 0)
and
#define LEGITIMIZE_ADDRESS(X,OLDX,MODE,WIN) \
{ \
if (GET_CODE (X) == PLUS && CONSTANT_ADDRESS_P (XEXP (X, 1))) \
(X) = gen_rtx (PLUS, SImode, XEXP (X, 0), \
copy_to_mode_reg (SImode, XEXP (X, 1))); \
if (GET_CODE (X) == PLUS && CONSTANT_ADDRESS_P (XEXP (X, 0))) \
(X) = gen_rtx (PLUS, SImode, XEXP (X, 1), \
copy_to_mode_reg (SImode, XEXP (X, 0))); \
if (GET_CODE (X) == PLUS && GET_CODE (XEXP (X, 0)) == MULT) \
(X) = gen_rtx (PLUS, SImode, XEXP (X, 1), \
force_operand (XEXP (X, 0), 0)); \
if (GET_CODE (X) == PLUS && GET_CODE (XEXP (X, 1)) == MULT) \
(X) = gen_rtx (PLUS, SImode, XEXP (X, 0), \
force_operand (XEXP (X, 1), 0)); \
if (GET_CODE (X) == PLUS && GET_CODE (XEXP (X, 0)) == PLUS) \
(X) = gen_rtx (PLUS, Pmode, force_operand (XEXP (X, 0), NULL_RTX),\
XEXP (X, 1)); \
if (GET_CODE (X) == PLUS && GET_CODE (XEXP (X, 1)) == PLUS) \
(X) = gen_rtx (PLUS, Pmode, XEXP (X, 0), \
force_operand (XEXP (X, 1), NULL_RTX)); \
if (GET_CODE (X) == SYMBOL_REF || GET_CODE (X) == CONST \
|| GET_CODE (X) == LABEL_REF) \
(X) = legitimize_address (flag_pic, X, 0, 0); \
if (memory_address_p (MODE, X)) \
goto WIN; }
and others. These macros get used multiple times of course. These are such
lovely candidates for macros, aren't they? :)
This code also nicely handles LLVM constructs that look like this:
if (isa<CastInst>(I))
...
else if (isa<BranchInst>(I))
...
else if (isa<SetCondInst>(I))
...
else if (isa<UnwindInst>(I))
...
else if (isa<VAArgInst>(I))
...
where the isa can obviously be a dyn_cast as well. Switch instructions are a
good thing.
llvm-svn: 11870
21e941fbfd