Add an option to disable codegen prepare critical edge splitting. In theory, PHI elimination is already doing all (most?) of the splitting needed. But machine-licm and machine-sink seem to miss some important optimizations when splitting is disabled.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@111224 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 14 insertions, 6 deletions

diff --git a/lib/Transforms/Scalar/CodeGenPrepare.cpp b/lib/Transforms/Scalar/CodeGenPrepare.cpp
index 823caceb2f..a4fcf6321e 100644
--- a/lib/Transforms/Scalar/CodeGenPrepare.cpp
+++ b/lib/Transforms/Scalar/CodeGenPrepare.cpp
@@ -33,6 +33,7 @@
 #include "llvm/ADT/SmallSet.h"
 #include "llvm/Assembly/Writer.h"
 #include "llvm/Support/CallSite.h"
+#include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/GetElementPtrTypeIterator.h"
 #include "llvm/Support/PatternMatch.h"
@@ -41,6 +42,11 @@
 using namespace llvm;
 using namespace llvm::PatternMatch;
 
+static cl::opt<bool>
+CriticalEdgeSplit("cgp-critical-edge-splitting",
+                  cl::desc("Split critical edges during codegen prepare"),
+                  cl::init(true), cl::Hidden);
+
 namespace {
   class CodeGenPrepare : public FunctionPass {
     /// TLI - Keep a pointer of a TargetLowering to consult for determining
@@ -891,12 +897,14 @@ bool CodeGenPrepare::OptimizeBlock(BasicBlock &BB) {
   bool MadeChange = false;
 
   // Split all critical edges where the dest block has a PHI.
-  TerminatorInst *BBTI = BB.getTerminator();
-  if (BBTI->getNumSuccessors() > 1 && !isa<IndirectBrInst>(BBTI)) {
-    for (unsigned i = 0, e = BBTI->getNumSuccessors(); i != e; ++i) {
-      BasicBlock *SuccBB = BBTI->getSuccessor(i);
-      if (isa<PHINode>(SuccBB->begin()) && isCriticalEdge(BBTI, i, true))
-        SplitEdgeNicely(BBTI, i, BackEdges, this);
+  if (CriticalEdgeSplit) {
+    TerminatorInst *BBTI = BB.getTerminator();
+    if (BBTI->getNumSuccessors() > 1 && !isa<IndirectBrInst>(BBTI)) {
+      for (unsigned i = 0, e = BBTI->getNumSuccessors(); i != e; ++i) {
+        BasicBlock *SuccBB = BBTI->getSuccessor(i);
+        if (isa<PHINode>(SuccBB->begin()) && isCriticalEdge(BBTI, i, true))
+          SplitEdgeNicely(BBTI, i, BackEdges, this);
+      }
     }
   }