================
@@ -2018,9 +2018,38 @@ bool GVNPass::performLoopLoadPRE(LoadInst *Load,
if (LoadPtr->canBeFreed())
return false;
- // TODO: Support critical edge splitting if blocker has more than 1
successor.
+ // The reload is inserted at the end of the chosen in-loop block so its value
+ // reaches the header along the path back to the latch. If that block has
+ // multiple successors, inserting there would also run the load on paths that
+ // leave the loop. Split the critical edge to the unique in-loop successor so
+ // the reload only runs on the path that feeds the header.
+ BasicBlock *InsertBlock = LoopBlock;
+ if (LoopBlock->getTerminator()->getNumSuccessors() != 1) {
+ BasicBlock *InLoopSucc = nullptr;
+ for (BasicBlock *Succ : successors(LoopBlock)) {
+ if (!L->contains(Succ))
+ continue;
+ // Bail if there is more than one in-loop successor: it is then unclear
+ // which edge carries the value back to the header.
+ if (InLoopSucc)
+ return false;
+ InLoopSucc = Succ;
+ }
+ if (!InLoopSucc)
+ return false;
+
+ // splitCriticalEdges() returns nullptr for edges it cannot split, e.g. an
+ // indirectbr terminator or an EH-pad successor; bail out in that case. The
+ // in-loop successor cannot be a backedge target here: LoopBlock does not
+ // dominate the latch, and a single-latch loop only has the latch->header
+ // backedge, so no critical loop backedge is split.
+ InsertBlock = splitCriticalEdges(LoopBlock, InLoopSucc);
----------------
madhur13490 wrote:
Done.
https://github.com/llvm/llvm-project/pull/206694
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