UnsafeGuaranteedPeephole: Handle exception edges correctly (#3471)

* UnsafeGuaranteedPeephole: Handle exception edges correctly

Exceptions can cause an exit before hitting the unsafeGuaranteedEnd instruction.
Make sure that we check post dominance to find such cases.

rdar://26890751
(cherry picked from commit 7cc447c)

* Adopt test case for swift-3.0-preview-3-branch

Author: aschwaighofer

lib/SILOptimizer/Transforms/UnsafeGuaranteedPeephole.cpp

@@ -37,6 +37,7 @@
 #include "swift/SIL/SILInstruction.h"
 #include "swift/SIL/SILModule.h"
 #include "swift/SILOptimizer/Analysis/ARCAnalysis.h"
+#include "swift/SILOptimizer/Analysis/DominanceAnalysis.h"
 #include "swift/SILOptimizer/Analysis/RCIdentityAnalysis.h"
 #include "swift/SILOptimizer/PassManager/Transforms.h"
 #include "swift/SILOptimizer/Utils/Local.h"
@@ -46,9 +47,14 @@ using namespace swift;
 /// Remove retain/release pairs around builtin "unsafeGuaranteed" instruction
 /// sequences.
 static bool removeGuaranteedRetainReleasePairs(SILFunction &F,
-                                               RCIdentityFunctionInfo &RCIA) {
+                                               RCIdentityFunctionInfo &RCIA,
+                                               PostDominanceAnalysis *PDA) {
   DEBUG(llvm::dbgs() << "Running on function " << F.getName() << "\n");
   bool Changed = false;
+
+  // Lazily compute post-dominance info only when we really need it.
+  PostDominanceInfo *PDI = nullptr;
+
   for (auto &BB : F) {
     auto It = BB.begin(), End = BB.end();
     llvm::DenseMap<SILValue, SILInstruction *> LastRetain;
@@ -119,6 +125,15 @@ static bool removeGuaranteedRetainReleasePairs(SILFunction &F,
         continue;
       }
 
+      if (!PDI)
+        PDI = PDA->get(&F);
+
+      // It needs to post-dominated the end instruction, since we need to remove
+      // the release along all paths to exit.
+      if (!PDI->properlyDominates(UnsafeGuaranteedEndI, UnsafeGuaranteedI))
+        continue;
+
+
       // Find the release to match with the unsafeGuaranteedValue.
       auto &UnsafeGuaranteedEndBB = *UnsafeGuaranteedEndI->getParent();
       auto LastRelease = findReleaseToMatchUnsafeGuaranteedValue(
@@ -165,7 +180,8 @@ class UnsafeGuaranteedPeephole : public swift::SILFunctionTransform {
 
   void run() override {
     auto &RCIA = *getAnalysis<RCIdentityAnalysis>()->get(getFunction());
-    if (removeGuaranteedRetainReleasePairs(*getFunction(), RCIA))
+    auto *PostDominance = getAnalysis<PostDominanceAnalysis>();
+    if (removeGuaranteedRetainReleasePairs(*getFunction(), RCIA, PostDominance))
       invalidateAnalysis(SILAnalysis::InvalidationKind::Instructions);
   }
 

test/SILOptimizer/unsafe_guaranteed_peephole.sil

@@ -14,6 +14,7 @@ public class Foo : Base {
 
 sil @beep : $@convention(thin) () -> ()
 sil @beep2 : $@convention(thin) (@owned Foo) -> ()
+sil @beep_or_throw : $@convention(thin) () -> @error ErrorProtocol
 
 // CHECK-LABEL: sil @testUnsafeGuaranteed_simple
 // CHECK: bb0([[P:%.*]] : $Foo):
@@ -513,3 +514,31 @@ bb0(%0 : $AnyObject, %1: $Builtin.Int32):
   %17 = tuple ()
   return %17 : $()
 }
+
+// CHECK-LABEL: sil @testUnsafeGuaranteed_throw
+// CHECK:bb0
+// CHECK: unsafeGuaranteed
+// CHECK:bb1
+// CHECK: unsafeGuaranteedEnd
+// CHECK: return
+// CHECK:bb2
+// CHECK: throw
+sil @testUnsafeGuaranteed_throw : $@convention(method) (@guaranteed Foo) -> @error ErrorProtocol {
+bb0(%0 : $Foo):
+  strong_retain %0 : $Foo
+  %4 = builtin "unsafeGuaranteed"<Foo>(%0 : $Foo) : $(Foo, Builtin.Int8)
+  %5 = tuple_extract %4 : $(Foo, Builtin.Int8), 0
+  %6 = tuple_extract %4 : $(Foo, Builtin.Int8), 1
+  %7 = function_ref @beep_or_throw : $@convention(thin) () -> @error ErrorProtocol
+  %8 = try_apply %7() : $@convention(thin) () -> @error ErrorProtocol, normal bb1, error bb2
+
+bb1(%15: $()):
+  strong_release %5 : $Foo
+  %16 = builtin "unsafeGuaranteedEnd"(%6 : $Builtin.Int8) : $()
+  %17 = tuple ()
+  return %17 : $()
+
+bb2(%9: $ErrorProtocol):
+  strong_release %5 : $Foo
+  throw  %9: $ErrorProtocol
+}