[PATCH] D100706: [LICM] Make capture check more precise

[Nikita Popov via Phabricator via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rGd440f9a326f0: [LICM] Make capture check more precise (authored by nikic).

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D100706/new/

https://reviews.llvm.org/D100706

Files:
  llvm/lib/Transforms/Scalar/LICM.cpp
  llvm/test/Transforms/LICM/promote-capture.ll


Index: llvm/test/Transforms/LICM/promote-capture.ll
===================================================================
--- llvm/test/Transforms/LICM/promote-capture.ll
+++ llvm/test/Transforms/LICM/promote-capture.ll
@@ -9,21 +9,24 @@
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[COUNT:%.*]] = alloca i32, align 4
 ; CHECK-NEXT:    store i32 0, i32* [[COUNT]], align 4
+; CHECK-NEXT:    [[COUNT_PROMOTED:%.*]] = load i32, i32* [[COUNT]], align 4
 ; CHECK-NEXT:    br label [[LOOP:%.*]]
 ; CHECK:       loop:
-; CHECK-NEXT:    [[I:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[I_NEXT:%.*]], [[LATCH:%.*]] ]
+; CHECK-NEXT:    [[C_INC2:%.*]] = phi i32 [ [[COUNT_PROMOTED]], [[ENTRY:%.*]] ], [ [[C_INC1:%.*]], [[LATCH:%.*]] ]
+; CHECK-NEXT:    [[I:%.*]] = phi i32 [ 0, [[ENTRY]] ], [ [[I_NEXT:%.*]], [[LATCH]] ]
 ; CHECK-NEXT:    [[COND:%.*]] = call i1 @cond(i32 [[I]])
 ; CHECK-NEXT:    br i1 [[COND]], label [[IF:%.*]], label [[LATCH]]
 ; CHECK:       if:
-; CHECK-NEXT:    [[C:%.*]] = load i32, i32* [[COUNT]], align 4
-; CHECK-NEXT:    [[C_INC:%.*]] = add i32 [[C]], 1
-; CHECK-NEXT:    store i32 [[C_INC]], i32* [[COUNT]], align 4
+; CHECK-NEXT:    [[C_INC:%.*]] = add i32 [[C_INC2]], 1
 ; CHECK-NEXT:    br label [[LATCH]]
 ; CHECK:       latch:
+; CHECK-NEXT:    [[C_INC1]] = phi i32 [ [[C_INC]], [[IF]] ], [ [[C_INC2]], [[LOOP]] ]
 ; CHECK-NEXT:    [[I_NEXT]] = add nuw i32 [[I]], 1
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[I_NEXT]], [[LEN:%.*]]
 ; CHECK-NEXT:    br i1 [[CMP]], label [[EXIT:%.*]], label [[LOOP]]
 ; CHECK:       exit:
+; CHECK-NEXT:    [[C_INC1_LCSSA:%.*]] = phi i32 [ [[C_INC1]], [[LATCH]] ]
+; CHECK-NEXT:    store i32 [[C_INC1_LCSSA]], i32* [[COUNT]], align 4
 ; CHECK-NEXT:    call void @capture(i32* [[COUNT]])
 ; CHECK-NEXT:    ret void
 ;
Index: llvm/lib/Transforms/Scalar/LICM.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/LICM.cpp
+++ llvm/lib/Transforms/Scalar/LICM.cpp
@@ -1954,10 +1954,21 @@
   }
 };
 
+bool isNotCapturedBeforeOrInLoop(const Value *V, const Loop *L,
+                                 DominatorTree *DT) {
+  // We can perform the captured-before check against any instruction in the
+  // loop header, as the loop header is reachable from any instruction inside
+  // the loop.
+  // TODO: ReturnCaptures=true shouldn't be necessary here.
+  return !PointerMayBeCapturedBefore(V, /* ReturnCaptures */ true,
+                                     /* StoreCaptures */ true,
+                                     L->getHeader()->getTerminator(), DT);
+}
 
 /// Return true iff we can prove that a caller of this function can not inspect
 /// the contents of the provided object in a well defined program.
-bool isKnownNonEscaping(Value *Object, const TargetLibraryInfo *TLI) {
+bool isKnownNonEscaping(Value *Object, const Loop *L,
+                        const TargetLibraryInfo *TLI, DominatorTree *DT) {
   if (isa<AllocaInst>(Object))
     // Since the alloca goes out of scope, we know the caller can't retain a
     // reference to it and be well defined.  Thus, we don't need to check for
@@ -1974,7 +1985,7 @@
   //      weaker condition and handle only AllocLikeFunctions (which are
   //      known to be noalias).  TODO
   return isAllocLikeFn(Object, TLI) &&
-    !PointerMayBeCaptured(Object, true, true);
+         isNotCapturedBeforeOrInLoop(Object, L, DT);
 }
 
 } // namespace
@@ -2060,7 +2071,7 @@
     // this by proving that the caller can't have a reference to the object
     // after return and thus can't possibly load from the object.
     Value *Object = getUnderlyingObject(SomePtr);
-    if (!isKnownNonEscaping(Object, TLI))
+    if (!isKnownNonEscaping(Object, CurLoop, TLI, DT))
       return false;
     // Subtlety: Alloca's aren't visible to callers, but *are* potentially
     // visible to other threads if captured and used during their lifetimes.
@@ -2195,7 +2206,7 @@
       Value *Object = getUnderlyingObject(SomePtr);
       SafeToInsertStore =
           (isAllocLikeFn(Object, TLI) || isa<AllocaInst>(Object)) &&
-          !PointerMayBeCaptured(Object, true, true);
+          isNotCapturedBeforeOrInLoop(Object, CurLoop, DT);
     }
   }
 


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