[llvm-commits] [llvm] r72661 - in /llvm/trunk: lib/Transforms/Scalar/GVN.cpp test/Transforms/GVN/pre-single-pred.ll
Owen Anderson
resistor at mac.com
Sun May 31 02:03:47 PDT 2009
Author: resistor
Date: Sun May 31 04:03:40 2009
New Revision: 72661
URL: http://llvm.org/viewvc/llvm-project?rev=72661&view=rev
Log:
Be more aggressive in doing LoadPRE by tracing backwards when a block only has
a single predecessor.
Patch by Jakub Staszak.
Added:
llvm/trunk/test/Transforms/GVN/pre-single-pred.ll
Modified:
llvm/trunk/lib/Transforms/Scalar/GVN.cpp
Modified: llvm/trunk/lib/Transforms/Scalar/GVN.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/GVN.cpp?rev=72661&r1=72660&r2=72661&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/GVN.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/GVN.cpp Sun May 31 04:03:40 2009
@@ -1055,11 +1055,29 @@
// that we only have to insert *one* load (which means we're basically moving
// the load, not inserting a new one).
- // Everything we do here is based on local predecessors of LI's block. If it
- // only has one predecessor, bail now.
+ SmallPtrSet<BasicBlock *, 4> Blockers;
+ for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i)
+ Blockers.insert(UnavailableBlocks[i]);
+
+ // Lets find first basic block with more than one predecessor. Walk backwards
+ // through predecessors if needed.
BasicBlock *LoadBB = LI->getParent();
- if (LoadBB->getSinglePredecessor())
- return false;
+ BasicBlock *TmpBB = LoadBB;
+
+ bool isSinglePred = false;
+ while (TmpBB->getSinglePredecessor()) {
+ isSinglePred = true;
+ TmpBB = TmpBB->getSinglePredecessor();
+ if (!TmpBB) // If haven't found any, bail now.
+ return false;
+ if (TmpBB == LoadBB) // Infinite (unreachable) loop.
+ return false;
+ if (Blockers.count(TmpBB))
+ return false;
+ }
+
+ assert(TmpBB);
+ LoadBB = TmpBB;
// If we have a repl set with LI itself in it, this means we have a loop where
// at least one of the values is LI. Since this means that we won't be able
@@ -1069,6 +1087,23 @@
if (ValuesPerBlock[i].second == LI)
return false;
+ if (isSinglePred) {
+ bool isHot = false;
+ for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i)
+ if (Instruction *I = dyn_cast<Instruction>(ValuesPerBlock[i].second))
+ // "Hot" Instruction is in some loop (because it dominates its dep.
+ // instruction).
+ if (DT->dominates(LI, I)) {
+ isHot = true;
+ break;
+ }
+
+ // We are interested only in "hot" instructions. We don't want to do any
+ // mis-optimizations here.
+ if (!isHot)
+ return false;
+ }
+
// Okay, we have some hope :). Check to see if the loaded value is fully
// available in all but one predecessor.
// FIXME: If we could restructure the CFG, we could make a common pred with
Added: llvm/trunk/test/Transforms/GVN/pre-single-pred.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/GVN/pre-single-pred.ll?rev=72661&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/GVN/pre-single-pred.ll (added)
+++ llvm/trunk/test/Transforms/GVN/pre-single-pred.ll Sun May 31 04:03:40 2009
@@ -0,0 +1,32 @@
+; RUN: llvm-as < %s | opt -gvn -enable-load-pre | llvm-dis | not grep {tmp3 = load}
+
+define i32 @f(i32* nocapture %p, i32 %n) nounwind {
+entry:
+ br label %for.cond
+
+for.cond: ; preds = %for.inc, %entry
+ %i.0 = phi i32 [ 0, %entry ], [ %indvar.next, %for.inc ] ; <i32> [#uses=2]
+ %cmp = icmp slt i32 %i.0, %n ; <i1> [#uses=1]
+ br i1 %cmp, label %for.body, label %for.cond.for.end_crit_edge
+
+for.cond.for.end_crit_edge: ; preds = %for.cond
+ br label %for.end
+
+for.body: ; preds = %for.cond
+ %tmp3 = load i32* %p ; <i32> [#uses=1]
+ %dec = add i32 %tmp3, -1 ; <i32> [#uses=2]
+ store i32 %dec, i32* %p
+ %cmp6 = icmp slt i32 %dec, 0 ; <i1> [#uses=1]
+ br i1 %cmp6, label %for.body.for.end_crit_edge, label %for.inc
+
+for.body.for.end_crit_edge: ; preds = %for.body
+ br label %for.end
+
+for.inc: ; preds = %for.body
+ %indvar.next = add i32 %i.0, 1 ; <i32> [#uses=1]
+ br label %for.cond
+
+for.end: ; preds = %for.body.for.end_crit_edge, %for.cond.for.end_crit_edge
+ %tmp9 = load i32* %p ; <i32> [#uses=1]
+ ret i32 %tmp9
+}
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