[PATCH] D59661: [GVN] Try to be more permissive with non-integral pointers zeros [NFCI]

[Jameson Nash via Phabricator via llvm-commits]

vtjnash updated this revision to Diff 228092.
vtjnash edited the summary of this revision.
vtjnash added a comment.
Herald added a subscriber: hiraditya.

Split commit into two pieces, each more clearly NFCI


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D59661/new/

https://reviews.llvm.org/D59661

Files:
  llvm/lib/Transforms/Utils/VNCoercion.cpp


Index: llvm/lib/Transforms/Utils/VNCoercion.cpp
===================================================================
--- llvm/lib/Transforms/Utils/VNCoercion.cpp
+++ llvm/lib/Transforms/Utils/VNCoercion.cpp
@@ -11,10 +11,8 @@
 namespace llvm {
 namespace VNCoercion {
 
-/// Return true if coerceAvailableValueToLoadType will succeed.
-bool canCoerceMustAliasedValueToLoad(Value *StoredVal, Type *LoadTy,
+bool canCoerceMustAliasedValueToLoad(Type *StoredTy, Type *LoadTy,
                                      const DataLayout &DL) {
-  Type *StoredTy = StoredVal->getType();
   if (StoredTy == LoadTy)
     return true;
 
@@ -35,19 +33,24 @@
     return false;
 
   // Don't coerce non-integral pointers to integers or vice versa.
-  if (DL.isNonIntegralPointerType(StoredVal->getType()->getScalarType()) !=
-      DL.isNonIntegralPointerType(LoadTy->getScalarType())) {
-    // As a special case, allow coercion of memset used to initialize
-    // an array w/null.  Despite non-integral pointers not generally having a
-    // specific bit pattern, we do assume null is zero.
-    if (auto *CI = dyn_cast<Constant>(StoredVal))
-      return CI->isNullValue();
+  if (DL.isNonIntegralPointerType(StoredTy->getScalarType()) !=
+      DL.isNonIntegralPointerType(LoadTy->getScalarType()))
     return false;
-  }
-  
+
   return true;
 }
 
+/// Return true if coerceAvailableValueToLoadType will succeed.
+bool canCoerceMustAliasedValueToLoad(Value *StoredVal, Type *LoadTy,
+                                     const DataLayout &DL) {
+    Type *StoredTy = StoredVal->getType();
+    if (auto *CI = dyn_cast<Constant>(StoredVal))
+      if (CI->isNullValue())
+        if (StoredTy == LoadTy || DL.getTypeSizeInBits(StoredTy) >= DL.getTypeSizeInBits(LoadTy))
+          return true;
+    return canCoerceMustAliasedValueToLoad(StoredTy, LoadTy, DL);
+}
+
 template <class T, class HelperClass>
 static T *coerceAvailableValueToLoadTypeHelper(T *StoredVal, Type *LoadedTy,
                                                HelperClass &Helper,
@@ -341,6 +344,9 @@
                                      HelperClass &Helper,
                                      const DataLayout &DL) {
   LLVMContext &Ctx = SrcVal->getType()->getContext();
+  if (auto *CI = dyn_cast<Constant>(GetUnderlyingObject(SrcVal, DL)))
+    if (CI->isNullValue())
+      return Constant::getNullValue(LoadTy);
 
   // If two pointers are in the same address space, they have the same size,
   // so we don't need to do any truncation, etc. This avoids introducing
@@ -468,6 +474,12 @@
     // memset(P, 'x', 1234) -> splat('x'), even if x is a variable, and
     // independently of what the offset is.
     T *Val = cast<T>(MSI->getValue());
+    if (auto *CI = dyn_cast<Constant>(Val)) {
+      // memset(P, '\0', 1234) -> just directly create the null value for *P
+      // by-passing any later validity checks
+      if (CI->isNullValue())
+        return Constant::getNullValue(LoadTy);
+    }
     if (LoadSize != 1)
       Val =
           Helper.CreateZExtOrBitCast(Val, IntegerType::get(Ctx, LoadSize * 8));


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