[llvm-commits] [llvm] r131841 - /llvm/trunk/lib/Target/README.txt

[Chris Lattner]

Author: lattner
Date: Sun May 22 00:45:06 2011
New Revision: 131841

URL: http://llvm.org/viewvc/llvm-project?rev=131841&view=rev
Log:
move PR9408 here.

Modified:
    llvm/trunk/lib/Target/README.txt

Modified: llvm/trunk/lib/Target/README.txt
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/README.txt?rev=131841&r1=131840&r2=131841&view=diff
==============================================================================
--- llvm/trunk/lib/Target/README.txt (original)
+++ llvm/trunk/lib/Target/README.txt Sun May 22 00:45:06 2011
@@ -2305,4 +2305,44 @@
 
 //===---------------------------------------------------------------------===//
 
+Machine level code hoisting can be useful in some cases.  For example, PR9408
+is about:
 
+typedef union {
+ void (*f1)(int);
+ void (*f2)(long);
+} funcs;
+
+void foo(funcs f, int which) {
+ int a = 5;
+ if (which) {
+   f.f1(a);
+ } else {
+   f.f2(a);
+ }
+}
+
+which we compile to:
+
+foo:                                    # @foo
+# BB#0:                                 # %entry
+       pushq   %rbp
+       movq    %rsp, %rbp
+       testl   %esi, %esi
+       movq    %rdi, %rax
+       je      .LBB0_2
+# BB#1:                                 # %if.then
+       movl    $5, %edi
+       callq   *%rax
+       popq    %rbp
+       ret
+.LBB0_2:                                # %if.else
+       movl    $5, %edi
+       callq   *%rax
+       popq    %rbp
+       ret
+
+Note that bb1 and bb2 are the same.  This doesn't happen at the IR level
+because one call is passing an i32 and the other is passing an i64.
+
+//===---------------------------------------------------------------------===//