From: Jingyue Wu <jingyue@google.com>
Date: Tue, 19 May 2015 20:52:45 +0000 (+0000)
Subject: [Speculation] NFC: more header comments
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=31d2ee7360cc28c2ca6c9ebb69deb4a21035ab05;p=llvm

[Speculation] NFC: more header comments

explaining how it differs from SpeculativeExecuteBB in SimplifyCFG.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@237724 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Transforms/Scalar/SpeculativeExecution.cpp b/lib/Transforms/Scalar/SpeculativeExecution.cpp
index d32e1094442..ff3f00a2e2f 100644
--- a/lib/Transforms/Scalar/SpeculativeExecution.cpp
+++ b/lib/Transforms/Scalar/SpeculativeExecution.cpp
@@ -41,6 +41,15 @@
 // Later passes sink back much of the speculated code that did not enable
 // further optimization.
 //
+// This pass is more aggressive than the function SpeculativeyExecuteBB in
+// SimplifyCFG. SimplifyCFG will not speculate if no selects are introduced and
+// it will speculate at most one instruction. It also will not speculate if
+// there is a value defined in the if-block that is only used in the then-block.
+// These restrictions make sense since the speculation in SimplifyCFG seems
+// aimed at introducing cheap selects, while this pass is intended to do more
+// aggressive speculation while counting on later passes to either capitalize on
+// that or clean it up.
+//
 //===----------------------------------------------------------------------===//
 
 #include "llvm/ADT/SmallSet.h"