diff options
Diffstat (limited to 'llvm/lib')
| -rw-r--r-- | llvm/lib/Target/X86/README.txt | 42 |
1 files changed, 41 insertions, 1 deletions
diff --git a/llvm/lib/Target/X86/README.txt b/llvm/lib/Target/X86/README.txt index 3bb92d1cad5..67eb2ce1a54 100644 --- a/llvm/lib/Target/X86/README.txt +++ b/llvm/lib/Target/X86/README.txt @@ -1612,8 +1612,48 @@ a mov. Something like: addl (%edx,%edi,4), %ebx addl %ebx, (%ecx,%edi,4) -Additionally, LSR should rewrite the exit condition of the loop to use +Here is another interesting example: + +void vertical_compose97iH1(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 miss the r/m/w opportunity here by using 2 subs instead of an add+sub[mem]: + +LBB9_2: # bb + movl (%ecx,%edi,4), %ebx + subl (%esi,%edi,4), %ebx + subl (%edx,%edi,4), %ebx + movl %ebx, (%ecx,%edi,4) + incl %edi + cmpl %eax, %edi + jne LBB9_2 # bb + +Additionally, LSR should rewrite the exit condition of these loops 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. //===---------------------------------------------------------------------===// + +We should be smarter about conversion from fpstack to XMM regs. + +double foo(); +void bar(double *P) { *P = foo(); } + +We compile that to: + +_bar: + subl $12, %esp + call L_foo$stub + fstpl (%esp) + movl 16(%esp), %eax + movsd (%esp), %xmm0 + movsd %xmm0, (%eax) + addl $12, %esp + ret + +for example. The magic to/from the stack is unneeded. + +//===---------------------------------------------------------------------===// |
