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50fad70279
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Chris Lattner 50fad70279 Teach LSR to strength reduce IVs that have a loop-invariant but non-constant stride. 
For code like this:

void foo(float *a, float *b, int n, int stride_a, int stride_b) {
  int i;
  for (i=0; i<n; i++)
      a[i*stride_a] = b[i*stride_b];
}

we now emit:

.LBB_foo2_2:    ; no_exit
        lfs f0, 0(r4)
        stfs f0, 0(r3)
        addi r7, r7, 1
        add r4, r2, r4
        add r3, r6, r3
        cmpw cr0, r7, r5
        blt .LBB_foo2_2 ; no_exit

instead of:

.LBB_foo_2:     ; no_exit
        mullw r8, r2, r7     ;; multiply!
        slwi r8, r8, 2
        lfsx f0, r4, r8
        mullw r8, r2, r6     ;; multiply!
        slwi r8, r8, 2
        stfsx f0, r3, r8
        addi r2, r2, 1
        cmpw cr0, r2, r5
        blt .LBB_foo_2  ; no_exit

loops with variable strides occur pretty often.  For example, in SPECFP2K
there are 317 variable strides in 177.mesa, 3 in 179.art, 14 in 188.ammp,
56 in 168.wupwise, 36 in 172.mgrid.

Now we can allow indvars to turn functions written like this:

void foo2(float *a, float *b, int n, int stride_a, int stride_b) {
  int i, ai = 0, bi = 0;
  for (i=0; i<n; i++)
    {
      a[ai] = b[bi];
      ai += stride_a;
      bi += stride_b;
    }
}

into code like the above for better analysis.  With this patch, they generate
identical code.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@22740 91177308-0d34-0410-b5e6-96231b3b80d8
2005-08-10 00:45:21 +00:00
..
Analysis implement two helper methods 2005-08-09 23:36:33 +00:00
Archive Final Changes For PR495: 2005-07-08 03:08:58 +00:00
AsmParser Fix grammar 2005-06-24 18:00:40 +00:00
Bytecode Eliminate all remaining tabs and trailing spaces. 2005-07-27 06:12:32 +00:00
CodeGen Fix spelling, fix some broken canonicalizations by my last patch 2005-08-09 23:09:05 +00:00
Debugger For PR495: 2005-07-07 23:21:43 +00:00
ExecutionEngine one cannot allocate a global, until one is done initializing the global pointers 2005-08-01 17:35:40 +00:00
Linker For PR495: 2005-07-07 23:21:43 +00:00
Support Allow tools with "consume after" options (like lli) to take more positional 2005-08-08 21:57:27 +00:00
System Fix grammar: it's == "it is". 2005-08-02 16:04:59 +00:00
Target add a optimization note 2005-08-09 22:30:57 +00:00
Transforms Teach LSR to strength reduce IVs that have a loop-invariant but non-constant stride. 2005-08-10 00:45:21 +00:00
VMCore add new helper function 2005-08-08 05:21:50 +00:00
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