[PATCH] D94180: [SimplifyCFG] Optimize CFG when null is passed to a function with nonnull argument.

[Dávid Bolvanský via Phabricator via llvm-commits]

xbolva00 created this revision.
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Example:

  __attribute__((nonnull,noinline)) char * pinc(char *p)  {
    return ++p;
  }
  
  char * foo(bool b, char *a) {
         return pinc(b ? 0 : a);
  
  
  }

optimize to

  char * foo(bool b, char *a) {
         return a;
  
  
  }


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D94180

Files:
  llvm/lib/Transforms/Utils/SimplifyCFG.cpp
  llvm/test/Transforms/SimplifyCFG/UnreachableEliminate.ll


Index: llvm/test/Transforms/SimplifyCFG/UnreachableEliminate.ll
===================================================================
--- llvm/test/Transforms/SimplifyCFG/UnreachableEliminate.ll
+++ llvm/test/Transforms/SimplifyCFG/UnreachableEliminate.ll
@@ -211,8 +211,9 @@
 ;
 ; CHECK-LABEL: @test9(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[SPEC_SELECT:%.*]] = select i1 [[X:%.*]], i8* null, i8* [[Y:%.*]]
-; CHECK-NEXT:    [[TMP0:%.*]] = call i8* @foo(i8* [[SPEC_SELECT]])
+; CHECK-NEXT:    [[TMP0:%.*]] = xor i1 [[X:%.*]], true
+; CHECK-NEXT:    call void @llvm.assume(i1 [[TMP0]])
+; CHECK-NEXT:    [[TMP1:%.*]] = call i8* @foo(i8* [[Y:%.*]])
 ; CHECK-NEXT:    ret void
 ;
 entry:
Index: llvm/lib/Transforms/Utils/SimplifyCFG.cpp
===================================================================
--- llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -6587,10 +6587,19 @@
                                       SI->getPointerAddressSpace())) &&
                SI->getPointerOperand() == I;
 
-    // A call to null is undefined.
-    if (auto *CB = dyn_cast<CallBase>(Use))
-      return !NullPointerIsDefined(CB->getFunction()) &&
-             CB->getCalledOperand() == I;
+    if (auto *CB = dyn_cast<CallBase>(Use)) {
+      if (NullPointerIsDefined(CB->getFunction()))
+        return false;
+      // A call to null is undefined.
+      if (CB->getCalledOperand() == I)
+        return true;
+
+      // Passing null to a nonnnull argument is undefined.
+      for (const llvm::Use &Arg : CB->args())
+        if (Arg == I &&
+            CB->paramHasAttr(CB->getArgOperandNo(&Arg), Attribute::NonNull))
+          return true;
+    }
   }
   return false;
 }


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