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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@45387 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2007-12-28 21:50:40 +00:00
parent 2910f68a52
commit 9bfcc624ba
1 changed files with 32 additions and 0 deletions
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32
lib/Target/X86/README.txt
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@ -1585,3 +1585,35 @@ movl $0, 124(%esp)
if the flags of the xor are dead.
//===---------------------------------------------------------------------===//
This testcase misses a read/modify/write opportunity (from PR1425):
void vertical_decompose97iH1(int *b0, int *b1, int *b2, int width){
int i;
for(i=0; i<width; i++)
b1[i] += (1*(b0[i] + b2[i])+0)>>0;
}
We compile it down to:
LBB1_2: # bb
movl (%esi,%edi,4), %ebx
addl (%ecx,%edi,4), %ebx
addl (%edx,%edi,4), %ebx
movl %ebx, (%ecx,%edi,4)
incl %edi
cmpl %eax, %edi
jne LBB1_2 # bb
the inner loop should add to the memory location (%ecx,%edi,4), saving
a mov. Something like:
movl (%esi,%edi,4), %ebx
addl (%edx,%edi,4), %ebx
addl %ebx, (%ecx,%edi,4)
Additionally, LSR should rewrite the exit condition of the loop to use
a stride-4 IV, would would allow all the scales in the loop to go away.
This would result in smaller code and more efficient microops.
//===---------------------------------------------------------------------===//