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[InstCombine] Allow sinking from unique predecessor with multiple edges 

Summary: We can allow sinking if the single user block has only one unique predecessor, regardless of the number of edges. Note that a switch statement with multiple cases can have the same destination.

Reviewers: mcrosier, majnemer, spatel, reames

Subscribers: reames, mcrosier, llvm-commits

Differential Revision: https://reviews.llvm.org/D23722

llvm-svn: 279448
This commit is contained in:
Jun Bum Lim 2016-08-22 18:21:56 +00:00
parent 475f4a763f
commit ec8b8cc595
2 changed files with 24 additions and 1 deletions
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2
llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
View File

@ -2903,7 +2903,7 @@ bool InstCombiner::run() {
// If the user is one of our immediate successors, and if that successor
// only has us as a predecessors (we'd have to split the critical edge
// otherwise), we can keep going.
if (UserIsSuccessor && UserParent->getSinglePredecessor()) {
if (UserIsSuccessor && UserParent->getUniquePredecessor()) {
// Okay, the CFG is simple enough, try to sink this instruction.
if (TryToSinkInstruction(I, UserParent)) {
DEBUG(dbgs() << "IC: Sink: " << *I << '\n');

23
llvm/test/Transforms/InstCombine/sink_instruction.ll
View File

@ -54,3 +54,26 @@ bb4: ; preds = %bb2
}
declare i32 @bar()
define i32 @test3(i32* nocapture readonly %P, i32 %i) {
entry:
%idxprom = sext i32 %i to i64
%arrayidx = getelementptr inbounds i32, i32* %P, i64 %idxprom
%0 = load i32, i32* %arrayidx, align 4
switch i32 %i, label %sw.epilog [
i32 5, label %sw.bb
i32 2, label %sw.bb
]
sw.bb: ; preds = %entry, %entry
; CHECK-LABEL: sw.bb:
; CHECK: %idxprom = sext i32 %i to i64
; CHECK: %arrayidx = getelementptr inbounds i32, i32* %P, i64 %idxprom
; CHECK: %0 = load i32, i32* %arrayidx, align 4
%add = add nsw i32 %0, %i
br label %sw.epilog
sw.epilog: ; preds = %entry, %sw.bb
%sum.0 = phi i32 [ %add, %sw.bb ], [ 0, %entry ]
ret i32 %sum.0
}