1 Target Independent Opportunities:
3 ===-------------------------------------------------------------------------===
5 FreeBench/mason contains code like this:
7 static p_type m0u(p_type p) {
8 int m[]={0, 8, 1, 2, 16, 5, 13, 7, 14, 9, 3, 4, 11, 12, 15, 10, 17, 6};
16 We currently compile this into a memcpy from a static array into 'm', then
17 a bunch of loads from m. It would be better to avoid the memcpy and just do
18 loads from the static array.
20 //===---------------------------------------------------------------------===//
22 Make the PPC branch selector target independant
24 //===---------------------------------------------------------------------===//
26 Get the C front-end to expand hypot(x,y) -> llvm.sqrt(x*x+y*y) when errno and
27 precision don't matter (ffastmath). Misc/mandel will like this. :)
29 //===---------------------------------------------------------------------===//
31 Solve this DAG isel folding deficiency:
49 The problem is the store's chain operand is not the load X but rather
50 a TokenFactor of the load X and load Y, which prevents the folding.
52 There are two ways to fix this:
54 1. The dag combiner can start using alias analysis to realize that y/x
55 don't alias, making the store to X not dependent on the load from Y.
56 2. The generated isel could be made smarter in the case it can't
57 disambiguate the pointers.
59 Number 1 is the preferred solution.
61 This has been "fixed" by a TableGen hack. But that is a short term workaround
62 which will be removed once the proper fix is made.
64 //===---------------------------------------------------------------------===//
66 On targets with expensive 64-bit multiply, we could LSR this:
73 for (i = ...; ++i, tmp+=tmp)
76 This would be a win on ppc32, but not x86 or ppc64.
78 //===---------------------------------------------------------------------===//
80 Shrink: (setlt (loadi32 P), 0) -> (setlt (loadi8 Phi), 0)
82 //===---------------------------------------------------------------------===//
84 Reassociate should turn: X*X*X*X -> t=(X*X) (t*t) to eliminate a multiply.
86 //===---------------------------------------------------------------------===//
88 Interesting? testcase for add/shift/mul reassoc:
90 int bar(int x, int y) {
91 return x*x*x+y+x*x*x*x*x*y*y*y*y;
93 int foo(int z, int n) {
94 return bar(z, n) + bar(2*z, 2*n);
97 //===---------------------------------------------------------------------===//
99 These two functions should generate the same code on big-endian systems:
101 int g(int *j,int *l) { return memcmp(j,l,4); }
102 int h(int *j, int *l) { return *j - *l; }
104 this could be done in SelectionDAGISel.cpp, along with other special cases,
107 //===---------------------------------------------------------------------===//
110 int rot(unsigned char b) { int a = ((b>>1) ^ (b<<7)) & 0xff; return a; }
112 Can be improved in two ways:
114 1. The instcombiner should eliminate the type conversions.
115 2. The X86 backend should turn this into a rotate by one bit.
117 //===---------------------------------------------------------------------===//
119 Add LSR exit value substitution. It'll probably be a win for Ackermann, etc.
121 //===---------------------------------------------------------------------===//
123 It would be nice to revert this patch:
124 http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20060213/031986.html
126 And teach the dag combiner enough to simplify the code expanded before
127 legalize. It seems plausible that this knowledge would let it simplify other
130 //===---------------------------------------------------------------------===//
132 For packed types, TargetData.cpp::getTypeInfo() returns alignment that is equal
133 to the type size. It works but can be overly conservative as the alignment of
134 specific packed types are target dependent.
136 //===---------------------------------------------------------------------===//
138 We should add 'unaligned load/store' nodes, and produce them from code like
141 v4sf example(float *P) {
142 return (v4sf){P[0], P[1], P[2], P[3] };
145 //===---------------------------------------------------------------------===//
147 We should constant fold packed type casts at the LLVM level, regardless of the
148 cast. Currently we cannot fold some casts because we don't have TargetData
149 information in the constant folder, so we don't know the endianness of the
152 //===---------------------------------------------------------------------===//
154 Add support for conditional increments, and other related patterns. Instead
159 je LBB16_2 #cond_next
170 //===---------------------------------------------------------------------===//
172 Combine: a = sin(x), b = cos(x) into a,b = sincos(x).
174 Expand these to calls of sin/cos and stores:
175 double sincos(double x, double *sin, double *cos);
176 float sincosf(float x, float *sin, float *cos);
177 long double sincosl(long double x, long double *sin, long double *cos);
179 Doing so could allow SROA of the destination pointers. See also:
180 http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17687
182 //===---------------------------------------------------------------------===//
184 Scalar Repl cannot currently promote this testcase to 'ret long cst':
186 %struct.X = type { int, int }
187 %struct.Y = type { %struct.X }
189 %retval = alloca %struct.Y, align 8 ; <%struct.Y*> [#uses=3]
190 %tmp12 = getelementptr %struct.Y* %retval, int 0, uint 0, uint 0
191 store int 0, int* %tmp12
192 %tmp15 = getelementptr %struct.Y* %retval, int 0, uint 0, uint 1
193 store int 1, int* %tmp15
194 %retval = cast %struct.Y* %retval to ulong*
195 %retval = load ulong* %retval ; <ulong> [#uses=1]
199 it should be extended to do so.
201 //===---------------------------------------------------------------------===//
203 Turn this into a single byte store with no load (the other 3 bytes are
206 void %test(uint* %P) {
208 %tmp14 = or uint %tmp, 3305111552
209 %tmp15 = and uint %tmp14, 3321888767
210 store uint %tmp15, uint* %P
214 //===---------------------------------------------------------------------===//
216 dag/inst combine "clz(x)>>5 -> x==0" for 32-bit x.
222 int t = __builtin_clz(x);
232 //===---------------------------------------------------------------------===//
234 Legalize should lower ctlz like this:
235 ctlz(x) = popcnt((x-1) & ~x)
237 on targets that have popcnt but not ctlz. itanium, what else?
239 //===---------------------------------------------------------------------===//
241 quantum_sigma_x in 462.libquantum contains the following loop:
243 for(i=0; i<reg->size; i++)
245 /* Flip the target bit of each basis state */
246 reg->node[i].state ^= ((MAX_UNSIGNED) 1 << target);
249 Where MAX_UNSIGNED/state is a 64-bit int. On a 32-bit platform it would be just
250 so cool to turn it into something like:
252 long long Res = ((MAX_UNSIGNED) 1 << target);
254 for(i=0; i<reg->size; i++)
255 reg->node[i].state ^= Res & 0xFFFFFFFFULL;
257 for(i=0; i<reg->size; i++)
258 reg->node[i].state ^= Res & 0xFFFFFFFF00000000ULL
261 ... which would only do one 32-bit XOR per loop iteration instead of two.
263 It would also be nice to recognize the reg->size doesn't alias reg->node[i], but
266 //===---------------------------------------------------------------------===//