[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

2 files changed, 24 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index 6424e083bd1..12c42ce6472 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -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');
diff --git a/llvm/test/Transforms/InstCombine/sink_instruction.ll b/llvm/test/Transforms/InstCombine/sink_instruction.ll
index 1bbd6b76384..4c057c66f7f 100644
--- a/llvm/test/Transforms/InstCombine/sink_instruction.ll
+++ b/llvm/test/Transforms/InstCombine/sink_instruction.ll
@@ -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
+}