| Target Independent Opportunities: |
| |
| //===---------------------------------------------------------------------===// |
| |
| With the recent changes to make the implicit def/use set explicit in |
| machineinstrs, we should change the target descriptions for 'call' instructions |
| so that the .td files don't list all the call-clobbered registers as implicit |
| defs. Instead, these should be added by the code generator (e.g. on the dag). |
| |
| This has a number of uses: |
| |
| 1. PPC32/64 and X86 32/64 can avoid having multiple copies of call instructions |
| for their different impdef sets. |
| 2. Targets with multiple calling convs (e.g. x86) which have different clobber |
| sets don't need copies of call instructions. |
| 3. 'Interprocedural register allocation' can be done to reduce the clobber sets |
| of calls. |
| |
| //===---------------------------------------------------------------------===// |
| |
| Make the PPC branch selector target independant |
| |
| //===---------------------------------------------------------------------===// |
| |
| Get the C front-end to expand hypot(x,y) -> llvm.sqrt(x*x+y*y) when errno and |
| precision don't matter (ffastmath). Misc/mandel will like this. :) |
| |
| //===---------------------------------------------------------------------===// |
| |
| Solve this DAG isel folding deficiency: |
| |
| int X, Y; |
| |
| void fn1(void) |
| { |
| X = X | (Y << 3); |
| } |
| |
| compiles to |
| |
| fn1: |
| movl Y, %eax |
| shll $3, %eax |
| orl X, %eax |
| movl %eax, X |
| ret |
| |
| The problem is the store's chain operand is not the load X but rather |
| a TokenFactor of the load X and load Y, which prevents the folding. |
| |
| There are two ways to fix this: |
| |
| 1. The dag combiner can start using alias analysis to realize that y/x |
| don't alias, making the store to X not dependent on the load from Y. |
| 2. The generated isel could be made smarter in the case it can't |
| disambiguate the pointers. |
| |
| Number 1 is the preferred solution. |
| |
| This has been "fixed" by a TableGen hack. But that is a short term workaround |
| which will be removed once the proper fix is made. |
| |
| //===---------------------------------------------------------------------===// |
| |
| On targets with expensive 64-bit multiply, we could LSR this: |
| |
| for (i = ...; ++i) { |
| x = 1ULL << i; |
| |
| into: |
| long long tmp = 1; |
| for (i = ...; ++i, tmp+=tmp) |
| x = tmp; |
| |
| This would be a win on ppc32, but not x86 or ppc64. |
| |
| //===---------------------------------------------------------------------===// |
| |
| Shrink: (setlt (loadi32 P), 0) -> (setlt (loadi8 Phi), 0) |
| |
| //===---------------------------------------------------------------------===// |
| |
| Reassociate should turn: X*X*X*X -> t=(X*X) (t*t) to eliminate a multiply. |
| |
| //===---------------------------------------------------------------------===// |
| |
| Interesting? testcase for add/shift/mul reassoc: |
| |
| int bar(int x, int y) { |
| return x*x*x+y+x*x*x*x*x*y*y*y*y; |
| } |
| int foo(int z, int n) { |
| return bar(z, n) + bar(2*z, 2*n); |
| } |
| |
| Reassociate should handle the example in GCC PR16157. |
| |
| //===---------------------------------------------------------------------===// |
| |
| These two functions should generate the same code on big-endian systems: |
| |
| int g(int *j,int *l) { return memcmp(j,l,4); } |
| int h(int *j, int *l) { return *j - *l; } |
| |
| this could be done in SelectionDAGISel.cpp, along with other special cases, |
| for 1,2,4,8 bytes. |
| |
| //===---------------------------------------------------------------------===// |
| |
| It would be nice to revert this patch: |
| http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20060213/031986.html |
| |
| And teach the dag combiner enough to simplify the code expanded before |
| legalize. It seems plausible that this knowledge would let it simplify other |
| stuff too. |
| |
| //===---------------------------------------------------------------------===// |
| |
| For vector types, TargetData.cpp::getTypeInfo() returns alignment that is equal |
| to the type size. It works but can be overly conservative as the alignment of |
| specific vector types are target dependent. |
| |
| //===---------------------------------------------------------------------===// |
| |
| We should add 'unaligned load/store' nodes, and produce them from code like |
| this: |
| |
| v4sf example(float *P) { |
| return (v4sf){P[0], P[1], P[2], P[3] }; |
| } |
| |
| //===---------------------------------------------------------------------===// |
| |
| We should constant fold vector type casts at the LLVM level, regardless of the |
| cast. Currently we cannot fold some casts because we don't have TargetData |
| information in the constant folder, so we don't know the endianness of the |
| target! |
| |
| //===---------------------------------------------------------------------===// |
| |
| Add support for conditional increments, and other related patterns. Instead |
| of: |
| |
| movl 136(%esp), %eax |
| cmpl $0, %eax |
| je LBB16_2 #cond_next |
| LBB16_1: #cond_true |
| incl _foo |
| LBB16_2: #cond_next |
| |
| emit: |
| movl _foo, %eax |
| cmpl $1, %edi |
| sbbl $-1, %eax |
| movl %eax, _foo |
| |
| //===---------------------------------------------------------------------===// |
| |
| Combine: a = sin(x), b = cos(x) into a,b = sincos(x). |
| |
| Expand these to calls of sin/cos and stores: |
| double sincos(double x, double *sin, double *cos); |
| float sincosf(float x, float *sin, float *cos); |
| long double sincosl(long double x, long double *sin, long double *cos); |
| |
| Doing so could allow SROA of the destination pointers. See also: |
| http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17687 |
| |
| //===---------------------------------------------------------------------===// |
| |
| Scalar Repl cannot currently promote this testcase to 'ret long cst': |
| |
| %struct.X = type { i32, i32 } |
| %struct.Y = type { %struct.X } |
| |
| define i64 @bar() { |
| %retval = alloca %struct.Y, align 8 |
| %tmp12 = getelementptr %struct.Y* %retval, i32 0, i32 0, i32 0 |
| store i32 0, i32* %tmp12 |
| %tmp15 = getelementptr %struct.Y* %retval, i32 0, i32 0, i32 1 |
| store i32 1, i32* %tmp15 |
| %retval.upgrd.1 = bitcast %struct.Y* %retval to i64* |
| %retval.upgrd.2 = load i64* %retval.upgrd.1 |
| ret i64 %retval.upgrd.2 |
| } |
| |
| it should be extended to do so. |
| |
| //===---------------------------------------------------------------------===// |
| |
| -scalarrepl should promote this to be a vector scalar. |
| |
| %struct..0anon = type { <4 x float> } |
| |
| define void @test1(<4 x float> %V, float* %P) { |
| %u = alloca %struct..0anon, align 16 |
| %tmp = getelementptr %struct..0anon* %u, i32 0, i32 0 |
| store <4 x float> %V, <4 x float>* %tmp |
| %tmp1 = bitcast %struct..0anon* %u to [4 x float]* |
| %tmp.upgrd.1 = getelementptr [4 x float]* %tmp1, i32 0, i32 1 |
| %tmp.upgrd.2 = load float* %tmp.upgrd.1 |
| %tmp3 = mul float %tmp.upgrd.2, 2.000000e+00 |
| store float %tmp3, float* %P |
| ret void |
| } |
| |
| //===---------------------------------------------------------------------===// |
| |
| Turn this into a single byte store with no load (the other 3 bytes are |
| unmodified): |
| |
| void %test(uint* %P) { |
| %tmp = load uint* %P |
| %tmp14 = or uint %tmp, 3305111552 |
| %tmp15 = and uint %tmp14, 3321888767 |
| store uint %tmp15, uint* %P |
| ret void |
| } |
| |
| //===---------------------------------------------------------------------===// |
| |
| dag/inst combine "clz(x)>>5 -> x==0" for 32-bit x. |
| |
| Compile: |
| |
| int bar(int x) |
| { |
| int t = __builtin_clz(x); |
| return -(t>>5); |
| } |
| |
| to: |
| |
| _bar: addic r3,r3,-1 |
| subfe r3,r3,r3 |
| blr |
| |
| //===---------------------------------------------------------------------===// |
| |
| Legalize should lower ctlz like this: |
| ctlz(x) = popcnt((x-1) & ~x) |
| |
| on targets that have popcnt but not ctlz. itanium, what else? |
| |
| //===---------------------------------------------------------------------===// |
| |
| quantum_sigma_x in 462.libquantum contains the following loop: |
| |
| for(i=0; i<reg->size; i++) |
| { |
| /* Flip the target bit of each basis state */ |
| reg->node[i].state ^= ((MAX_UNSIGNED) 1 << target); |
| } |
| |
| Where MAX_UNSIGNED/state is a 64-bit int. On a 32-bit platform it would be just |
| so cool to turn it into something like: |
| |
| long long Res = ((MAX_UNSIGNED) 1 << target); |
| if (target < 32) { |
| for(i=0; i<reg->size; i++) |
| reg->node[i].state ^= Res & 0xFFFFFFFFULL; |
| } else { |
| for(i=0; i<reg->size; i++) |
| reg->node[i].state ^= Res & 0xFFFFFFFF00000000ULL |
| } |
| |
| ... which would only do one 32-bit XOR per loop iteration instead of two. |
| |
| It would also be nice to recognize the reg->size doesn't alias reg->node[i], but |
| alas... |
| |
| //===---------------------------------------------------------------------===// |
| |
| This isn't recognized as bswap by instcombine: |
| |
| unsigned int swap_32(unsigned int v) { |
| v = ((v & 0x00ff00ffU) << 8) | ((v & 0xff00ff00U) >> 8); |
| v = ((v & 0x0000ffffU) << 16) | ((v & 0xffff0000U) >> 16); |
| return v; |
| } |
| |
| Nor is this (yes, it really is bswap): |
| |
| unsigned long reverse(unsigned v) { |
| unsigned t; |
| t = v ^ ((v << 16) | (v >> 16)); |
| t &= ~0xff0000; |
| v = (v << 24) | (v >> 8); |
| return v ^ (t >> 8); |
| } |
| |
| //===---------------------------------------------------------------------===// |
| |
| These should turn into single 16-bit (unaligned?) loads on little/big endian |
| processors. |
| |
| unsigned short read_16_le(const unsigned char *adr) { |
| return adr[0] | (adr[1] << 8); |
| } |
| unsigned short read_16_be(const unsigned char *adr) { |
| return (adr[0] << 8) | adr[1]; |
| } |
| |
| //===---------------------------------------------------------------------===// |
| |
| -instcombine should handle this transform: |
| icmp pred (sdiv X / C1 ), C2 |
| when X, C1, and C2 are unsigned. Similarly for udiv and signed operands. |
| |
| Currently InstCombine avoids this transform but will do it when the signs of |
| the operands and the sign of the divide match. See the FIXME in |
| InstructionCombining.cpp in the visitSetCondInst method after the switch case |
| for Instruction::UDiv (around line 4447) for more details. |
| |
| The SingleSource/Benchmarks/Shootout-C++/hash and hash2 tests have examples of |
| this construct. |
| |
| //===---------------------------------------------------------------------===// |
| |
| Instcombine misses several of these cases (see the testcase in the patch): |
| http://gcc.gnu.org/ml/gcc-patches/2006-10/msg01519.html |
| |
| //===---------------------------------------------------------------------===// |
| |
| viterbi speeds up *significantly* if the various "history" related copy loops |
| are turned into memcpy calls at the source level. We need a "loops to memcpy" |
| pass. |
| |
| //===---------------------------------------------------------------------===// |
| |
| Consider: |
| |
| typedef unsigned U32; |
| typedef unsigned long long U64; |
| int test (U32 *inst, U64 *regs) { |
| U64 effective_addr2; |
| U32 temp = *inst; |
| int r1 = (temp >> 20) & 0xf; |
| int b2 = (temp >> 16) & 0xf; |
| effective_addr2 = temp & 0xfff; |
| if (b2) effective_addr2 += regs[b2]; |
| b2 = (temp >> 12) & 0xf; |
| if (b2) effective_addr2 += regs[b2]; |
| effective_addr2 &= regs[4]; |
| if ((effective_addr2 & 3) == 0) |
| return 1; |
| return 0; |
| } |
| |
| Note that only the low 2 bits of effective_addr2 are used. On 32-bit systems, |
| we don't eliminate the computation of the top half of effective_addr2 because |
| we don't have whole-function selection dags. On x86, this means we use one |
| extra register for the function when effective_addr2 is declared as U64 than |
| when it is declared U32. |
| |
| //===---------------------------------------------------------------------===// |
| |
| Promote for i32 bswap can use i64 bswap + shr. Useful on targets with 64-bit |
| regs and bswap, like itanium. |
| |
| //===---------------------------------------------------------------------===// |
| |
| LSR should know what GPR types a target has. This code: |
| |
| volatile short X, Y; // globals |
| |
| void foo(int N) { |
| int i; |
| for (i = 0; i < N; i++) { X = i; Y = i*4; } |
| } |
| |
| produces two identical IV's (after promotion) on PPC/ARM: |
| |
| LBB1_1: @bb.preheader |
| mov r3, #0 |
| mov r2, r3 |
| mov r1, r3 |
| LBB1_2: @bb |
| ldr r12, LCPI1_0 |
| ldr r12, [r12] |
| strh r2, [r12] |
| ldr r12, LCPI1_1 |
| ldr r12, [r12] |
| strh r3, [r12] |
| add r1, r1, #1 <- [0,+,1] |
| add r3, r3, #4 |
| add r2, r2, #1 <- [0,+,1] |
| cmp r1, r0 |
| bne LBB1_2 @bb |
| |
| |
| //===---------------------------------------------------------------------===// |
| |
| Tail call elim should be more aggressive, checking to see if the call is |
| followed by an uncond branch to an exit block. |
| |
| ; This testcase is due to tail-duplication not wanting to copy the return |
| ; instruction into the terminating blocks because there was other code |
| ; optimized out of the function after the taildup happened. |
| ;RUN: llvm-upgrade < %s | llvm-as | opt -tailcallelim | llvm-dis | not grep call |
| |
| int %t4(int %a) { |
| entry: |
| %tmp.1 = and int %a, 1 |
| %tmp.2 = cast int %tmp.1 to bool |
| br bool %tmp.2, label %then.0, label %else.0 |
| |
| then.0: |
| %tmp.5 = add int %a, -1 |
| %tmp.3 = call int %t4( int %tmp.5 ) |
| br label %return |
| |
| else.0: |
| %tmp.7 = setne int %a, 0 |
| br bool %tmp.7, label %then.1, label %return |
| |
| then.1: |
| %tmp.11 = add int %a, -2 |
| %tmp.9 = call int %t4( int %tmp.11 ) |
| br label %return |
| |
| return: |
| %result.0 = phi int [ 0, %else.0 ], [ %tmp.3, %then.0 ], |
| [ %tmp.9, %then.1 ] |
| ret int %result.0 |
| } |
| |
| //===---------------------------------------------------------------------===// |
| |
| Argument promotion should promote arguments for recursive functions, like |
| this: |
| |
| ; RUN: llvm-upgrade < %s | llvm-as | opt -argpromotion | llvm-dis | grep x.val |
| |
| implementation ; Functions: |
| |
| internal int %foo(int* %x) { |
| entry: |
| %tmp = load int* %x |
| %tmp.foo = call int %foo(int *%x) |
| ret int %tmp.foo |
| } |
| |
| int %bar(int* %x) { |
| entry: |
| %tmp3 = call int %foo( int* %x) ; <int>[#uses=1] |
| ret int %tmp3 |
| } |
| |
| |
| |