There is no EndPtr anymore - reinterpret the original comment in terms

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

diff --git a/lib/Target/README.txt b/lib/Target/README.txt
index 90afe3640ce7d961332861fdaff55de1e4c7639b..6d42d812a00bf3753843531996f3021a0d60c792 100644 (file)
--- a/lib/Target/README.txt
+++ b/lib/Target/README.txt
@@ -2,6 +2,38 @@ Target Independent Opportunities:
 
 //===---------------------------------------------------------------------===//
 
+We should recognize idioms for add-with-carry and turn it into the appropriate
+intrinsics.  This example:
+
+unsigned add32carry(unsigned sum, unsigned x) {
+ unsigned z = sum + x;
+ if (sum + x < x)
+     z++;
+ return z;
+}
+
+Compiles to: clang t.c -S -o - -O3 -fomit-frame-pointer -m64 -mkernel
+
+_add32carry:                            ## @add32carry
+       addl    %esi, %edi
+       cmpl    %esi, %edi
+       sbbl    %eax, %eax
+       andl    $1, %eax
+       addl    %edi, %eax
+       ret
+
+with clang, but to:
+
+_add32carry:
+       leal    (%rsi,%rdi), %eax
+       cmpl    %esi, %eax
+       adcl    $0, %eax
+       ret
+
+with gcc.
+
+//===---------------------------------------------------------------------===//
+
 Dead argument elimination should be enhanced to handle cases when an argument is
 dead to an externally visible function.  Though the argument can't be removed
 from the externally visible function, the caller doesn't need to pass it in.
@@ -906,17 +938,6 @@ The expression should optimize to something like
 
 //===---------------------------------------------------------------------===//
 
-From GCC Bug 3756:
-int
-pn (int n)
-{
- return (n >= 0 ? 1 : -1);
-}
-Should combine to (n >> 31) | 1.  Currently not optimized with "clang
--emit-llvm-bc | opt -std-compile-opts | llc".
-
-//===---------------------------------------------------------------------===//
-
 void a(int variable)
 {
  if (variable == 4 || variable == 6)
@@ -1319,12 +1340,6 @@ void foo (int a, struct T b)
 
 simplifylibcalls should do several optimizations for strspn/strcspn:
 
-strcspn(x, "") -> strlen(x)
-strcspn("", x) -> 0
-strspn("", x) -> 0
-strspn(x, "") -> strlen(x)
-strspn(x, "a") -> strchr(x, 'a')-x
-
 strcspn(x, "a") -> inlined loop for up to 3 letters (similarly for strspn):
 
 size_t __strcspn_c3 (__const char *__s, int __reject1, int __reject2,
@@ -1930,5 +1945,41 @@ something like the following, which eliminates a branch:
        ret
 .LBB0_2:
        jmp     foo  # TAILCALL
+//===---------------------------------------------------------------------===//
+Given a branch where the two target blocks are identical ("ret i32 %b" in
+both), simplifycfg will simplify them away. But not so for a switch statement:
+
+define i32 @f(i32 %a, i32 %b) nounwind readnone {
+entry:
+        switch i32 %a, label %bb3 [
+                i32 4, label %bb
+                i32 6, label %bb
+        ]
+
+bb:             ; preds = %entry, %entry
+        ret i32 %b
+
+bb3:            ; preds = %entry
+        ret i32 %b
+}
+//===---------------------------------------------------------------------===//
+
+clang -O3 fails to devirtualize this virtual inheritance case: (GCC PR45875)
+
+struct c1 {};
+struct c10 : c1{
+  virtual void foo ();
+};
+struct c11 : c10, c1{
+  virtual void f6 ();
+};
+struct c28 : virtual c11{
+  void f6 ();
+};
+void check_c28 () {
+  c28 obj;
+  c11 *ptr = &obj;
+  ptr->f6 ();
+}
 
 //===---------------------------------------------------------------------===//