Introduce a new technique for merging BasicBlock with Instruction sentinel by superpo...

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

diff --git a/lib/Target/README.txt b/lib/Target/README.txt
index 4e4668698ad2b09fc44ed2990843ac56a6fe8b91..341c5c1ff472f9f683fbc87384b4a44b9b0a2bc1 100644 (file)
--- a/lib/Target/README.txt
+++ b/lib/Target/README.txt
@@ -1651,3 +1651,73 @@ 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
+
+//===---------------------------------------------------------------------===//
+
+Instcombine should replace the load with a constant in:
+
+  static const char x[4] = {'a', 'b', 'c', 'd'};
+  
+  unsigned int y(void) {
+    return *(unsigned int *)x;
+  }
+
+It currently only does this transformation when the size of the constant 
+is the same as the size of the integer (so, try x[5]) and the last byte 
+is a null (making it a C string). There's no need for these restrictions.
+
+//===---------------------------------------------------------------------===//
+