Be bug compatible with gcc by returning MMX values in RAX.

[oota-llvm.git] / lib / Target / README.txt

diff --git a/lib/Target/README.txt b/lib/Target/README.txt
index 4e4668698ad2b09fc44ed2990843ac56a6fe8b91..09e5433578cca167a85d32f1a0d680452ee0b237 100644 (file)
--- a/lib/Target/README.txt
+++ b/lib/Target/README.txt
@@ -1651,3 +1651,56 @@ globalopt to remove the "stored only" global.
 
 //===---------------------------------------------------------------------===//
 
+This code:
+
+define inreg i32 @foo(i8* inreg %p) nounwind {
+  %tmp0 = load i8* %p
+  %tmp1 = ashr i8 %tmp0, 5
+  %tmp2 = sext i8 %tmp1 to i32
+  ret i32 %tmp2
+}
+
+could be dagcombine'd to a sign-extending load with a shift.
+For example, on x86 this currently gets this:
+
+       movb    (%eax), %al
+       sarb    $5, %al
+       movsbl  %al, %eax
+
+while it could get this:
+
+       movsbl  (%eax), %eax
+       sarl    $5, %eax
+
+//===---------------------------------------------------------------------===//
+
+GCC PR31029:
+
+int test(int x) { return 1-x == x; }     // --> return false
+int test2(int x) { return 2-x == x; }    // --> return x == 1 ?
+
+Always foldable for odd constants, what is the rule for even?
+
+//===---------------------------------------------------------------------===//
+
+PR 3381: GEP to field of size 0 inside a struct could be turned into GEP
+for next field in struct (which is at same address).
+
+For example: store of float into { {{}}, float } could be turned into a store to
+the float directly.
+
+//===---------------------------------------------------------------------===//
+#include <math.h>
+double foo(double a) {    return sin(a); }
+
+This compiles into this on x86-64 Linux:
+foo:
+       subq    $8, %rsp
+       call    sin
+       addq    $8, %rsp
+       ret
+vs:
+
+foo:
+        jmp sin
+