Changes in directory llvm/lib/Transforms/Utils:
LoopSimplify.cpp updated: 1.71 -> 1.72
---
Log message:
Don't attempt to split subloops out of a loop with a huge number of backedges.
Not only will this take huge amounts of compile time, the resultant loop nests
won't be useful for optimization. This reduces loopsimplify time on
Transforms/LoopSimplify/2006-08-11-LoopSimplifyLongTime.ll from ~32s to ~0.4s
with a debug build of llvm on a 2.7Ghz G5.
---
Diffs of the changes: (+19 -8)
LoopSimplify.cpp | 27 +++++++++++++++++++--------
1 files changed, 19 insertions(+), 8 deletions(-)
Index: llvm/lib/Transforms/Utils/LoopSimplify.cpp
diff -u llvm/lib/Transforms/Utils/LoopSimplify.cpp:1.71
llvm/lib/Transforms/Utils/LoopSimplify.cpp:1.72
--- llvm/lib/Transforms/Utils/LoopSimplify.cpp:1.71 Fri Aug 11 23:51:20 2006
+++ llvm/lib/Transforms/Utils/LoopSimplify.cpp Sat Aug 12 00:25:00 2006
@@ -168,6 +168,8 @@
///
bool LoopSimplify::ProcessLoop(Loop *L) {
bool Changed = false;
+ReprocessLoop:
+
// Canonicalize inner loops before outer loops. Inner loop canonicalization
// can provide work for the outer loop to canonicalize.
for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I)
@@ -208,16 +210,25 @@
// If the header has more than two predecessors at this point (from the
// preheader and from multiple backedges), we must adjust the loop.
- if (L->getNumBackEdges() != 1) {
-
- // If this is really a nested loop, rip it out into a child loop.
- if (Loop *NL = SeparateNestedLoop(L)) {
- ++NumNested;
- // This is a big restructuring change, reprocess the whole loop.
- ProcessLoop(NL);
- return true;
+ unsigned NumBackedges = L->getNumBackEdges();
+ if (NumBackedges != 1) {
+ // If this is really a nested loop, rip it out into a child loop. Don't do
+ // this for loops with a giant number of backedges, just factor them into a
+ // common backedge instead.
+ if (NumBackedges < 8) {
+ if (Loop *NL = SeparateNestedLoop(L)) {
+ ++NumNested;
+ // This is a big restructuring change, reprocess the whole loop.
+ ProcessLoop(NL);
+ Changed = true;
+ // GCC doesn't tail recursion eliminate this.
+ goto ReprocessLoop;
+ }
}
+ // If we either couldn't, or didn't want to, identify nesting of the loops,
+ // insert a new block that all backedges target, then make it jump to the
+ // loop header.
InsertUniqueBackedgeBlock(L);
NumInserted++;
Changed = true;
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