[llvm] ddd9ec6 - [LICM] Update comments related to escape check (NFC)

[Nikita Popov via llvm-commits]

Author: Nikita Popov
Date: 2022-01-06T14:45:48+01:00
New Revision: ddd9ec667a2e3ec241f11dbb8368600dcf432eb4

URL: https://github.com/llvm/llvm-project/commit/ddd9ec667a2e3ec241f11dbb8368600dcf432eb4
DIFF: https://github.com/llvm/llvm-project/commit/ddd9ec667a2e3ec241f11dbb8368600dcf432eb4.diff

LOG: [LICM] Update comments related to escape check (NFC)

The comments here were outdated and a bit confusing without the
knowledge that we're only guarding against reads on unwind.

Added: 
    

Modified: 
    llvm/lib/Transforms/Scalar/LICM.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Scalar/LICM.cpp b/llvm/lib/Transforms/Scalar/LICM.cpp
index 80ed671b0a52..ebb2520a0516 100644
--- a/llvm/lib/Transforms/Scalar/LICM.cpp
+++ b/llvm/lib/Transforms/Scalar/LICM.cpp
@@ -1923,9 +1923,9 @@ bool isNotCapturedBeforeOrInLoop(const Value *V, const Loop *L,
                                      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 Loop *L, DominatorTree *DT) {
+/// Return true if we can prove that a caller cannot inspect the object if an
+/// unwind occurs inside the loop.
+bool isNotVisibleOnUnwind(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
@@ -1933,12 +1933,12 @@ bool isKnownNonEscaping(Value *Object, const Loop *L, DominatorTree *DT) {
     return true;
 
   // For all other objects we need to know that the caller can't possibly
-  // have gotten a reference to the object.  There are two components of
-  // that:
-  //   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.
+  // have gotten a reference to the object prior to an unwind in the loop.
+  // There are two components of that:
+  //   1) Object can't have been captured prior to the definition site.
+  //      For this, we need to know the return value is noalias.
+  //   1) Object can't be captured before or inside the loop.  This is what
+  //      isNotCapturedBeforeOrInLoop() checks.
   return isNoAliasCall(Object) && isNotCapturedBeforeOrInLoop(Object, L, DT);
 }
 
@@ -2026,7 +2026,7 @@ bool llvm::promoteLoopAccessesToScalars(
     // 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, DT))
+    if (!isNotVisibleOnUnwind(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.