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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
autoconf Fix PR608: 2005-07-27 21:58:38 +00:00
docs Update a doc, patch contributed by Jim Laskey! 2005-08-02 19:14:25 +00:00
examples Eliminate all remaining tabs and trailing spaces. 2005-07-27 06:12:32 +00:00
include/llvm add two helper methods 2005-08-09 23:36:18 +00:00
lib Teach LSR to strength reduce IVs that have a loop-invariant but non-constant stride. 2005-08-10 00:45:21 +00:00
projects oops 2005-07-05 16:36:18 +00:00
runtime Remove trailing whitespace 2005-04-21 23:48:37 +00:00
test new testcase 2005-08-10 00:33:01 +00:00
tools If the user interrupts bugpoint, don't extract loops 2005-08-02 23:25:56 +00:00
utils make is the standard name, not gmake 2005-08-02 00:10:52 +00:00
win32 Fix VC++ build problems. 2005-07-30 18:22:27 +00:00
.cvsignore Ignore the configure.out file generated by "make reconfigure" 2005-06-18 23:01:25 +00:00
configure Fix PR608: 2005-07-27 21:58:38 +00:00
CREDITS.TXT Add a note, people are responsible for requesting that they be added to the 2005-08-02 22:10:21 +00:00
LICENSE.TXT Remove extraneous colons after program names for consistency 2005-05-12 21:39:01 +00:00
llvm.spec Onward to LLVM-1.6 and beyond! 2005-05-18 20:23:20 +00:00
llvm.spec.in Onward to LLVM-1.6 and beyond! 2005-05-18 20:23:20 +00:00
Makefile Make sure the tools get built if no build target is specified. 2005-05-29 00:49:24 +00:00
Makefile.common Update comments to reflect new variable names. Patch contributed by 2005-02-14 16:02:19 +00:00
Makefile.config.in Two changes: 2005-04-22 17:14:14 +00:00
Makefile.rules No, really, it's an Alpha! And you probably thought it was a PowerPC. 2005-07-22 22:43:40 +00:00
README.txt Make the text of this file a little more useful. 2004-09-02 22:49:27 +00:00

README.txt 

Low Level Virtual Machine (LLVM)
================================

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