From: Daniel Dunbar <daniel@zuster.org>
Date: Fri, 20 Feb 2009 19:34:45 +0000 (+0000)
Subject: Add some IRgen improvement notes.
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=e6a90167aa29c126ce5d0398faedbbba582df7c3;p=clang

Add some IRgen improvement notes.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@65146 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/CodeGen/README.txt b/lib/CodeGen/README.txt
index 56069dd99d..ea2cf8cf0e 100644
--- a/lib/CodeGen/README.txt
+++ b/lib/CodeGen/README.txt
@@ -30,3 +30,20 @@ block.
 
 //===---------------------------------------------------------------------===//
 
+We should try and avoid generating basic blocks which only contain
+jumps. At -O0, this penalizes us all the way from IRgen (malloc &
+instruction overhead), all the way down through code generation and
+assembly time.
+
+On 176.gcc:expr.ll, it looks like over 12% of basic blocks are just
+direct branches.
+
+//===---------------------------------------------------------------------===//
+
+There are some more places where we could avoid generating unreachable code. For
+example:
+  void f0(int a) { abort(); if (a) printf("hi"); }
+still generates a call to printf. This doesn't occur much in real
+code, but would still be nice to clean up.
+
+//===---------------------------------------------------------------------===//