Enable tail merging on PPC.

Tail merging had been disabled on PPC because it would disturb bundling decisions
made during pre-RA scheduling on the 970 cores. Now, however, all bundling decisions
are made during post-RA scheduling, and tail merging is generally beneficial (the
average test-suite speedup is insignificantly positive).

Largest test-suite speedups:
MultiSource/Benchmarks/mediabench/gsm/toast/toast - 30%
MultiSource/Benchmarks/BitBench/uuencode/uuencode - 23%
SingleSource/Benchmarks/Shootout-C++/ary - 21%
SingleSource/Benchmarks/Stanford/Queens - 17%

Largest slowdowns:
MultiSource/Benchmarks/MiBench/security-sha/security-sha - 24%
MultiSource/Benchmarks/McCat/03-testtrie/testtrie - 22%
MultiSource/Applications/JM/ldecod/ldecod - 14%
MultiSource/Benchmarks/mediabench/g721/g721encode/encode - 9%

This is improved by using full (instead of just critical) anti-dependency breaking,
but doing so still causes miscompiles and so cannot yet be enabled by default.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@158259 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Target/PowerPC/PPCTargetMachine.cpp b/lib/Target/PowerPC/PPCTargetMachine.cpp
index b9c703e708dbf1b138c9cc224671a2a6660d2153..d7a808855bbb4f50640857363b862c690a735e0e 100644 (file)
--- a/lib/Target/PowerPC/PPCTargetMachine.cpp
+++ b/lib/Target/PowerPC/PPCTargetMachine.cpp
@@ -93,13 +93,7 @@ public:
 } // namespace
 
 TargetPassConfig *PPCTargetMachine::createPassConfig(PassManagerBase &PM) {
-  TargetPassConfig *PassConfig = new PPCPassConfig(this, PM);
-
-  // Override this for PowerPC.  Tail merging happily breaks up instruction issue
-  // groups, which typically degrades performance.
-  PassConfig->setEnableTailMerge(false);
-
-  return PassConfig;
+  return new PPCPassConfig(this, PM);
 }
 
 bool PPCPassConfig::addPreRegAlloc() {

diff --git a/test/CodeGen/PowerPC/2007-05-22-tailmerge-3.ll b/test/CodeGen/PowerPC/2007-05-22-tailmerge-3.ll
index c1415510d05f3f43d97c6529d77d1f18153259c1..382ba1f6a82d5419e765ae61ed5ed2bb790e2e63 100644 (file)
--- a/test/CodeGen/PowerPC/2007-05-22-tailmerge-3.ll
+++ b/test/CodeGen/PowerPC/2007-05-22-tailmerge-3.ll
@@ -1,8 +1,8 @@
-; RUN: llc < %s -march=ppc32 | grep bl.*baz | count 2
-; RUN: llc < %s -march=ppc32 | grep bl.*quux | count 2
-; RUN: llc < %s -march=ppc32 -enable-tail-merge | grep bl.*baz | count 1
-; RUN: llc < %s -march=ppc32 -enable-tail-merge=1 | grep bl.*quux | count 1
-; Check that tail merging is not the default on ppc, and that -enable-tail-merge works.
+; RUN: llc < %s -march=ppc32 -enable-tail-merge=0 | grep bl.*baz | count 2
+; RUN: llc < %s -march=ppc32 -enable-tail-merge=0 | grep bl.*quux | count 2
+; RUN: llc < %s -march=ppc32 | grep bl.*baz | count 1
+; RUN: llc < %s -march=ppc32 | grep bl.*quux | count 1
+; Check that tail merging is the default on ppc, and that -enable-tail-merge works.
 
 ; ModuleID = 'tail.c'
 target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64"