[llvm] 56d228a - [SimplifyCFG] Update passingValueIsAlwaysUndefined to check more attributes

[Juneyoung Lee via llvm-commits]

Author: Juneyoung Lee
Date: 2021-02-24T10:40:50+09:00
New Revision: 56d228a14e3631de157ae98dd61d21193e4502d5

URL: https://github.com/llvm/llvm-project/commit/56d228a14e3631de157ae98dd61d21193e4502d5
DIFF: https://github.com/llvm/llvm-project/commit/56d228a14e3631de157ae98dd61d21193e4502d5.diff

LOG: [SimplifyCFG] Update passingValueIsAlwaysUndefined to check more attributes

This is a simple patch to update SimplifyCFG's passingValueIsAlwaysUndefined to inspect more attributes.

A new function `CallBase::isPassingUndefUB` checks attributes that imply noundef.

Reviewed By: spatel

Differential Revision: https://reviews.llvm.org/D97244

Added: 
    

Modified: 
    llvm/include/llvm/IR/InstrTypes.h
    llvm/lib/Transforms/Utils/SimplifyCFG.cpp
    llvm/test/Transforms/SimplifyCFG/UnreachableEliminate.ll

Removed: 
    


################################################################################
diff  --git a/llvm/include/llvm/IR/InstrTypes.h b/llvm/include/llvm/IR/InstrTypes.h
index 01a51edaf909..60668892497f 100644
--- a/llvm/include/llvm/IR/InstrTypes.h
+++ b/llvm/include/llvm/IR/InstrTypes.h
@@ -1653,6 +1653,17 @@ class CallBase : public Instruction {
            paramHasAttr(ArgNo, Attribute::Preallocated);
   }
 
+  /// Determine whether passing undef to this argument is undefined behavior.
+  /// If passing undef to this argument is UB, passing poison is UB as well
+  /// because poison is more undefined than undef.
+  bool isPassingUndefUB(unsigned ArgNo) const {
+    return paramHasAttr(ArgNo, Attribute::NoUndef) ||
+           // dereferenceable implies noundef.
+           paramHasAttr(ArgNo, Attribute::Dereferenceable) ||
+           // dereferenceable implies noundef, and null is a well-defined value.
+           paramHasAttr(ArgNo, Attribute::DereferenceableOrNull);
+  }
+
   /// Determine if there are is an inalloca argument. Only the last argument can
   /// have the inalloca attribute.
   bool hasInAllocaArgument() const {

diff  --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index df851c1b4a4c..30d9daf844b3 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -6433,8 +6433,8 @@ static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I, bool PtrValu
         for (const llvm::Use &Arg : CB->args())
           if (Arg == I) {
             unsigned ArgIdx = CB->getArgOperandNo(&Arg);
-            if (CB->paramHasAttr(ArgIdx, Attribute::NonNull) &&
-                CB->paramHasAttr(ArgIdx, Attribute::NoUndef)) {
+            if (CB->isPassingUndefUB(ArgIdx) &&
+                CB->paramHasAttr(ArgIdx, Attribute::NonNull)) {
               // Passing null to a nonnnull+noundef argument is undefined.
               return !PtrValueMayBeModified;
             }
@@ -6444,7 +6444,7 @@ static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I, bool PtrValu
         for (const llvm::Use &Arg : CB->args())
           if (Arg == I) {
             unsigned ArgIdx = CB->getArgOperandNo(&Arg);
-            if (CB->paramHasAttr(ArgIdx, Attribute::NoUndef)) {
+            if (CB->isPassingUndefUB(ArgIdx)) {
               // Passing undef to a noundef argument is undefined.
               return true;
             }

diff  --git a/llvm/test/Transforms/SimplifyCFG/UnreachableEliminate.ll b/llvm/test/Transforms/SimplifyCFG/UnreachableEliminate.ll
index af8682df8afd..cdec29415bc6 100644
--- a/llvm/test/Transforms/SimplifyCFG/UnreachableEliminate.ll
+++ b/llvm/test/Transforms/SimplifyCFG/UnreachableEliminate.ll
@@ -234,8 +234,9 @@ else:
 define void @test9_deref(i1 %X, i8* %Y) {
 ; CHECK-LABEL: @test9_deref(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[SPEC_SELECT:%.*]] = select i1 [[X:%.*]], i8* null, i8* [[Y:%.*]]
-; CHECK-NEXT:    [[TMP0:%.*]] = call i8* @fn_nonnull_deref_arg(i8* [[SPEC_SELECT]])
+; CHECK-NEXT:    [[TMP0:%.*]] = xor i1 [[X:%.*]], true
+; CHECK-NEXT:    call void @llvm.assume(i1 [[TMP0]])
+; CHECK-NEXT:    [[TMP1:%.*]] = call i8* @fn_nonnull_deref_arg(i8* [[Y:%.*]])
 ; CHECK-NEXT:    ret void
 ;
 entry:
@@ -254,8 +255,9 @@ else:
 define void @test9_deref_or_null(i1 %X, i8* %Y) {
 ; CHECK-LABEL: @test9_deref_or_null(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[SPEC_SELECT:%.*]] = select i1 [[X:%.*]], i8* null, i8* [[Y:%.*]]
-; CHECK-NEXT:    [[TMP0:%.*]] = call i8* @fn_nonnull_deref_or_null_arg(i8* [[SPEC_SELECT]])
+; CHECK-NEXT:    [[TMP0:%.*]] = xor i1 [[X:%.*]], true
+; CHECK-NEXT:    call void @llvm.assume(i1 [[TMP0]])
+; CHECK-NEXT:    [[TMP1:%.*]] = call i8* @fn_nonnull_deref_or_null_arg(i8* [[Y:%.*]])
 ; CHECK-NEXT:    ret void
 ;
 entry: