Revert r361811: 'Re-commit r357452 (take 2): "SimplifyCFG SinkCommonCodeFromPredecessors ...'

We have observed some failures with internal builds with this revision.

- Performance regressions:
  - llvm's SingleSource/Misc evalloop shows performance regressions (although these may be red herrings).
  - Benchmarks for Abseil's SwissTable.
- Correctness:
  - Failures for particular libicu tests when building the Google AppEngine SDK (for PHP).

hwennborg has already been notified, and is aware of reproducer failures.

llvm-svn: 363220

1 files changed, 14 insertions, 15 deletions

diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 69df6549cb1..90b552035af 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -1445,10 +1445,9 @@ HoistTerminator:
 static bool canSinkInstructions(
     ArrayRef<Instruction *> Insts,
     DenseMap<Instruction *, SmallVector<Value *, 4>> &PHIOperands) {
-  // Prune out obviously bad instructions to move. Each instruction must have
-  // exactly zero or one use, and we check later that use is by a single, common
-  // PHI instruction in the successor.
-  bool HasUse = !Insts.front()->user_empty();
+  // Prune out obviously bad instructions to move. Any non-store instruction
+  // must have exactly one use, and we check later that use is by a single,
+  // common PHI instruction in the successor.
   for (auto *I : Insts) {
     // These instructions may change or break semantics if moved.
     if (isa<PHINode>(I) || I->isEHPad() || isa<AllocaInst>(I) ||
@@ -1462,10 +1461,9 @@ static bool canSinkInstructions(
       if (C->isInlineAsm())
         return false;
 
-    // Each instruction must have zero or one use.
-    if (HasUse && !I->hasOneUse())
-      return false;
-    if (!HasUse && !I->user_empty())
+    // Everything must have only one use too, apart from stores which
+    // have no uses.
+    if (!isa<StoreInst>(I) && !I->hasOneUse())
       return false;
   }
 
@@ -1474,11 +1472,11 @@ static bool canSinkInstructions(
     if (!I->isSameOperationAs(I0))
       return false;
 
-  // All instructions in Insts are known to be the same opcode. If they have a
-  // use, check that the only user is a PHI or in the same block as the
-  // instruction, because if a user is in the same block as an instruction we're
-  // contemplating sinking, it must already be determined to be sinkable.
-  if (HasUse) {
+  // All instructions in Insts are known to be the same opcode. If they aren't
+  // stores, check the only user of each is a PHI or in the same block as the
+  // instruction, because if a user is in the same block as an instruction
+  // we're contemplating sinking, it must already be determined to be sinkable.
+  if (!isa<StoreInst>(I0)) {
     auto *PNUse = dyn_cast<PHINode>(*I0->user_begin());
     auto *Succ = I0->getParent()->getTerminator()->getSuccessor(0);
     if (!all_of(Insts, [&PNUse,&Succ](const Instruction *I) -> bool {
@@ -1556,7 +1554,7 @@ static bool sinkLastInstruction(ArrayRef<BasicBlock*> Blocks) {
   // it is slightly over-aggressive - it gets confused by commutative instructions
   // so double-check it here.
   Instruction *I0 = Insts.front();
-  if (!I0->user_empty()) {
+  if (!isa<StoreInst>(I0)) {
     auto *PNUse = dyn_cast<PHINode>(*I0->user_begin());
     if (!all_of(Insts, [&PNUse](const Instruction *I) -> bool {
           auto *U = cast<Instruction>(*I->user_begin());
@@ -1614,10 +1612,11 @@ static bool sinkLastInstruction(ArrayRef<BasicBlock*> Blocks) {
       I0->andIRFlags(I);
     }
 
-  if (!I0->user_empty()) {
+  if (!isa<StoreInst>(I0)) {
     // canSinkLastInstruction checked that all instructions were used by
     // one and only one PHI node. Find that now, RAUW it to our common
     // instruction and nuke it.
+    assert(I0->hasOneUse());
     auto *PN = cast<PHINode>(*I0->user_begin());
     PN->replaceAllUsesWith(I0);
     PN->eraseFromParent();