[PATCH] D78575: [Analysis] recognize the 'null' pointer constant as not poison

[Sanjay Patel via Phabricator via llvm-commits]

spatel created this revision.
spatel added reviewers: aqjune, lebedev.ri, nikic.
Herald added subscribers: hiraditya, mcrosier.

Just making sure that I'm not missing some corner-case for pointers here...
This is needed to create a safe-constant-substitution alternate to D78430 <https://reviews.llvm.org/D78430>.


https://reviews.llvm.org/D78575

Files:
  llvm/lib/Analysis/ValueTracking.cpp
  llvm/test/Transforms/InstSimplify/freeze.ll


Index: llvm/test/Transforms/InstSimplify/freeze.ll
===================================================================
--- llvm/test/Transforms/InstSimplify/freeze.ll
+++ llvm/test/Transforms/InstSimplify/freeze.ll
@@ -51,12 +51,9 @@
   ret i32()* %k
 }
 
-; TODO: This is not poison.
-
 define i32* @make_const_null() {
 ; CHECK-LABEL: @make_const_null(
-; CHECK-NEXT:    [[K:%.*]] = freeze i32* null
-; CHECK-NEXT:    ret i32* [[K]]
+; CHECK-NEXT:    ret i32* null
 ;
   %k = freeze i32* null
   ret i32* %k
@@ -208,8 +205,7 @@
 
 define i32* @gep_inbounds_null() {
 ; CHECK-LABEL: @gep_inbounds_null(
-; CHECK-NEXT:    [[K:%.*]] = freeze i32* null
-; CHECK-NEXT:    ret i32* [[K]]
+; CHECK-NEXT:    ret i32* null
 ;
   %p = getelementptr inbounds i32, i32* null, i32 0
   %k = freeze i32* %p
Index: llvm/lib/Analysis/ValueTracking.cpp
===================================================================
--- llvm/lib/Analysis/ValueTracking.cpp
+++ llvm/lib/Analysis/ValueTracking.cpp
@@ -4693,8 +4693,9 @@
     if (isa<UndefValue>(C) || isa<ConstantExpr>(C))
       return false;
 
-    // TODO: Add ConstantFP and pointers.
-    if (isa<ConstantInt>(C) || isa<GlobalVariable>(C) )
+    // TODO: Add ConstantFP.
+    if (isa<ConstantInt>(C) || isa<GlobalVariable>(C) ||
+        isa<ConstantPointerNull>(C))
       return true;
 
     if (C->getType()->isVectorTy())


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