[SystemZ] README: remove an implemented idea, add some new ones

The note about conditional returns can now be removed, as they are implemented. Let's also add 2 new ones in exchange. Author: koriakin Differential Revision: http://reviews.llvm.org/D18962 llvm-svn: 265944
llvm · Apr 11, 2016 · aa04768 · aa04768
1 parent 1bac911
commit aa04768
Showing 1 changed file with 13 additions and 5 deletions.
diff --git a/llvm/lib/Target/SystemZ/README.txt b/llvm/lib/Target/SystemZ/README.txt
@@ -43,11 +43,6 @@ We don't use the BRANCH ON INDEX instructions.
 
 --
 
-We might want to use BRANCH ON CONDITION for conditional indirect calls
-and conditional returns.
-
---
-
 We don't use the TEST DATA CLASS instructions.
 
 --
@@ -166,3 +161,16 @@ If needed, we can support 16-byte atomics using LPQ, STPQ and CSDG.
 
 We might want to model all access registers and use them to spill
 32-bit values.
+
+--
+
+We might want to use 'j .+2' as a trap instruction, like gcc does.  It can
+also be made conditional like the return instruction, allowing us to utilize
+compare-and-trap and load-and-trap instructions.
+
+--
+
+We might want to use the 'overflow' condition of eg. AR to support
+llvm.sadd.with.overflow.i32 and related instructions - the generated code
+for signed overflow check is currently quite bad.  This would improve
+the results of using -ftrapv.