[PATCH] D116728: [LICM] Check for noalias call instead of alloc like fn

[Nikita Popov via Phabricator via llvm-commits]

nikic created this revision.
nikic added reviewers: reames, fhahn, asbirlea.
Herald added subscribers: jeroen.dobbelaere, hiraditya.
nikic requested review of this revision.
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Herald added a subscriber: llvm-commits.

When determining whether the memory is local to the function (and we can thus introduce spurious writes without thread-safety issues), check for a noalias call rather than the hardcoded list of memory allocation functions. Noalias calls are the more general way to determine allocation functions, as long as we're only interested in the property that the returned value is distinct from any other accessible memory.


https://reviews.llvm.org/D116728

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


Index: llvm/test/Transforms/LICM/promote-tls.ll
===================================================================
--- llvm/test/Transforms/LICM/promote-tls.ll
+++ llvm/test/Transforms/LICM/promote-tls.ll
@@ -156,15 +156,18 @@
 ; CHECK-NEXT:    [[EXITCMP:%.*]] = icmp eq i8* [[GUARD]], null
 ; CHECK-NEXT:    br i1 [[EXITCMP]], label [[FOR_BODY]], label [[EARLY_EXIT:%.*]]
 ; CHECK:       early-exit:
+; CHECK-NEXT:    [[NEW1_LCSSA:%.*]] = phi i32 [ [[NEW1]], [[FOR_HEADER]] ]
+; CHECK-NEXT:    store i32 [[NEW1_LCSSA]], i32* [[ADDR]], align 4
 ; CHECK-NEXT:    ret i32* null
 ; CHECK:       for.body:
 ; CHECK-NEXT:    [[NEW]] = add i32 [[NEW1]], 1
-; CHECK-NEXT:    store i32 [[NEW]], i32* [[ADDR]], align 4
 ; CHECK-NEXT:    [[INC]] = add nsw i32 [[I_02]], 1
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i32 [[INC]], [[N:%.*]]
 ; CHECK-NEXT:    br i1 [[CMP]], label [[FOR_HEADER]], label [[FOR_COND_FOR_END_CRIT_EDGE:%.*]]
 ; CHECK:       for.cond.for.end_crit_edge:
+; CHECK-NEXT:    [[NEW_LCSSA:%.*]] = phi i32 [ [[NEW]], [[FOR_BODY]] ]
 ; CHECK-NEXT:    [[SPLIT:%.*]] = phi i32* [ [[ADDR]], [[FOR_BODY]] ]
+; CHECK-NEXT:    store i32 [[NEW_LCSSA]], i32* [[ADDR]], align 4
 ; CHECK-NEXT:    ret i32* null
 ;
 entry:
Index: llvm/lib/Transforms/Scalar/LICM.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/LICM.cpp
+++ llvm/lib/Transforms/Scalar/LICM.cpp
@@ -1925,8 +1925,7 @@
 
 /// 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 Loop *L,
-                        const TargetLibraryInfo *TLI, DominatorTree *DT) {
+bool isKnownNonEscaping(Value *Object, const Loop *L, 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
@@ -1939,11 +1938,8 @@
   //   1) Object can't be escaped by this function.  This is what
   //      PointerMayBeCaptured checks.
   //   2) Object can't have been captured at definition site.  For this, we
-  //      need to know the return value is noalias.  At the moment, we use a
-  //      weaker condition and handle only AllocLikeFunctions (which are
-  //      known to be noalias).  TODO
-  return isAllocLikeFn(Object, TLI) &&
-         isNotCapturedBeforeOrInLoop(Object, L, DT);
+  //      need to know the return value is noalias.
+  return isNoAliasCall(Object) && isNotCapturedBeforeOrInLoop(Object, L, DT);
 }
 
 } // namespace
@@ -2030,7 +2026,7 @@
     // 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, CurLoop, TLI, DT))
+    if (!isKnownNonEscaping(Object, CurLoop, 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.
@@ -2163,7 +2159,7 @@
     else {
       Value *Object = getUnderlyingObject(SomePtr);
       SafeToInsertStore =
-          (isAllocLikeFn(Object, TLI) || isa<AllocaInst>(Object)) &&
+          (isNoAliasCall(Object) || isa<AllocaInst>(Object)) &&
           isNotCapturedBeforeOrInLoop(Object, CurLoop, DT);
     }
   }


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