implement rdar://6653118 - fastisel should fold loads where possible.

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

diff --git a/lib/Target/README.txt b/lib/Target/README.txt
index 90afe3640ce7d961332861fdaff55de1e4c7639b..4faf8bcfd419982b438c73c5758e88e8f6840cce 100644 (file)
--- a/lib/Target/README.txt
+++ b/lib/Target/README.txt
@@ -906,17 +906,6 @@ 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)
@@ -1930,5 +1919,21 @@ 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
+}
 //===---------------------------------------------------------------------===//