Author: lattner
Date: Mon Dec 24 13:32:55 2007
New Revision: 45344
URL: http://llvm.org/viewvc/llvm-project?rev=45344&view=rev
Log:
add a -backedge-hack llc-beta option to codegenprepare.
When specified, don't split backedges of single-bb loops.
This helps address PR1877
Modified:
llvm/trunk/lib/Transforms/Scalar/CodeGenPrepare.cpp
Modified: llvm/trunk/lib/Transforms/Scalar/CodeGenPrepare.cpp
URL:
http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/CodeGenPrepare.cpp?rev=45344&r1=45343&r2=45344&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/CodeGenPrepare.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/CodeGenPrepare.cpp Mon Dec 24 13:32:55 2007
@@ -37,6 +37,8 @@
namespace {
cl::opt<bool> OptExtUses("optimize-ext-uses",
cl::init(true), cl::Hidden);
+ // LLCBETA option.
+ cl::opt<bool> DontHackBackedge("backedge-hack", cl::Hidden);
}
namespace {
@@ -264,7 +266,7 @@
}
-/// SplitEdgeNicely - Split the critical edge from TI to it's specified
+/// SplitEdgeNicely - Split the critical edge from TI to its specified
/// successor if it will improve codegen. We only do this if the successor has
/// phi nodes (otherwise critical edges are ok). If there is already another
/// predecessor of the succ that is empty (and thus has no phi nodes), use it
@@ -275,9 +277,15 @@
assert(isa<PHINode>(Dest->begin()) &&
"This should only be called if Dest has a PHI!");
+ // As a hack, never split backedges of loops. Even though the copy for any
+ // PHIs inserted on the backedge would be dead for exits from the loop, we
+ // assume that the cost of *splitting* the backedge would be too high.
+ if (DontHackBackedge && Dest == TIBB)
+ return;
+
/// TIPHIValues - This array is lazily computed to determine the values of
/// PHIs in Dest that TI would provide.
- std::vector<Value*> TIPHIValues;
+ SmallVector<Value*, 32> TIPHIValues;
// Check to see if Dest has any blocks that can be used as a split edge for
// this terminator.
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