https://llvm.org/bugs/show_bug.cgi?id=31468
Bug ID: 31468
Summary: NewGVN doesn't merge unconditional branches.
Product: libraries
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: normal
Priority: P
Component: Scalar Optimizations
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected]
Blocks: 30995
Classification: Unclassified
The code living in GVN.cpp claims this is done to expose "more PRE
opportunities". Fair enough, but I'm not entirely sure this is relevant anymore
in NewGVN as we're writing a real PRE infrastructure.
Fixing is relatively trivial (patch inline), but not sure if really needed.
Dan, what you think? If we don't want to change this code, I'll modify the
failing test and call it a day (basic.ll)
diff --git a/lib/Transforms/Scalar/NewGVN.cpp
b/lib/Transforms/Scalar/NewGVN.cpp
index 1f12d10..430385a 100644
--- a/lib/Transforms/Scalar/NewGVN.cpp
+++ b/lib/Transforms/Scalar/NewGVN.cpp
@@ -1378,6 +1378,20 @@ bool NewGVN::runGVN(Function &F, DominatorTree *_DT,
AssumptionCache *_AC,
unsigned ICount = 0;
SmallPtrSet<BasicBlock *, 16> VisitedBlocks;
+ // Do a sweep over all the basic blocks to merge unconditional branches.
+ for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE;) {
+ BasicBlock *BB = &*FI++;
+
+ // In theory here we could pass MemSSA if/when MergeBlockIntoPredecessor
+ // will grow version which accepts the analysis.
+ bool removedBlock = MergeBlockIntoPredecessor(
+ BB, DT, nullptr /* LoopInfo */, nullptr /* MemDep */);
+
+ if (removedBlock)
+ NumGVNBlocksDeleted++;
+ Changed |= removedBlock;
+ }
+
// Note: We want RPO traversal of the blocks, which is not quite the same as
// dominator tree order, particularly with regard whether backedges get
// visited first or second, given a block with multiple successors.
diff --git a/test/Transforms/NewGVN/basic.ll b/test/Transforms/NewGVN/basic.ll
index f6670aa..f68823a 100644
--- a/test/Transforms/NewGVN/basic.ll
+++ b/test/Transforms/NewGVN/basic.ll
@@ -1,4 +1,3 @@
-; XFAIL: *
; RUN: opt < %s -newgvn -S | FileCheck %s
define i32 @main() {
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