Author: lattner
Date: Fri Dec 28 23:51:58 2007
New Revision: 45397
URL: http://llvm.org/viewvc/llvm-project?rev=45397&view=rev
Log:
add a note
Modified:
llvm/trunk/lib/Target/X86/README.txt
Modified: llvm/trunk/lib/Target/X86/README.txt
URL:
http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/README.txt?rev=45397&r1=45396&r2=45397&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/README.txt (original)
+++ llvm/trunk/lib/Target/X86/README.txt Fri Dec 28 23:51:58 2007
@@ -1612,8 +1612,48 @@
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.
+
+//===---------------------------------------------------------------------===//
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