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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@45397 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Target/X86/README.txt b/lib/Target/X86/README.txt
index 3bb92d1cad532bd5ec9fbaa67227e3cefe788761..67eb2ce1a545c1140a86aab8fc2b97bd277c1118 100644 (file)
--- a/lib/Target/X86/README.txt
+++ b/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.
+
+//===---------------------------------------------------------------------===//