[PATCH] D144563: [SimplifyCFG] Improve the precision of `PtrValueMayBeModified`

[DianQK via Phabricator via llvm-commits]

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Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D144563

Files:
  llvm/lib/Transforms/Utils/SimplifyCFG.cpp
  llvm/test/Transforms/SimplifyCFG/UnreachableEliminate.ll
  llvm/test/Transforms/SimplifyCFG/unreachable-eliminate-on-ret.ll


Index: llvm/test/Transforms/SimplifyCFG/unreachable-eliminate-on-ret.ll
===================================================================
--- llvm/test/Transforms/SimplifyCFG/unreachable-eliminate-on-ret.ll
+++ llvm/test/Transforms/SimplifyCFG/unreachable-eliminate-on-ret.ll
@@ -55,7 +55,26 @@
 ; CHECK-LABEL: @test_ret_ptr_nonnull_noundef_gep_nonzero(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[SPEC_SELECT:%.*]] = select i1 [[COND:%.*]], ptr [[X:%.*]], ptr null
-; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds ptr, ptr [[SPEC_SELECT]], i64 12
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr ptr, ptr [[SPEC_SELECT]], i64 12
+; CHECK-NEXT:    ret ptr [[GEP]]
+;
+entry:
+  br i1 %cond, label %bb1, label %bb2
+
+bb1:
+  br label %bb2
+
+bb2:
+  %phi = phi ptr [ null, %entry ], [ %x, %bb1 ]
+  %gep = getelementptr ptr, ptr %phi, i64 12
+  ret ptr %gep
+}
+
+define nonnull noundef ptr @test_ret_ptr_nonnull_noundef_gep_inbounds_nonzero(i1 %cond, ptr %x) {
+; CHECK-LABEL: @test_ret_ptr_nonnull_noundef_gep_inbounds_nonzero(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    call void @llvm.assume(i1 [[COND:%.*]])
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds ptr, ptr [[X:%.*]], i64 12
 ; CHECK-NEXT:    ret ptr [[GEP]]
 ;
 entry:
Index: llvm/test/Transforms/SimplifyCFG/UnreachableEliminate.ll
===================================================================
--- llvm/test/Transforms/SimplifyCFG/UnreachableEliminate.ll
+++ llvm/test/Transforms/SimplifyCFG/UnreachableEliminate.ll
@@ -444,9 +444,10 @@
 define void @test9_gep_inbounds_nonzero(i1 %X, ptr %Y) {
 ; CHECK-LABEL: @test9_gep_inbounds_nonzero(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[SPEC_SELECT:%.*]] = select i1 [[X:%.*]], ptr null, ptr [[Y:%.*]]
-; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds i8, ptr [[SPEC_SELECT]], i64 12
-; CHECK-NEXT:    [[TMP0:%.*]] = call ptr @fn_nonnull_noundef_arg(ptr [[GEP]])
+; CHECK-NEXT:    [[TMP0:%.*]] = xor i1 [[X:%.*]], true
+; CHECK-NEXT:    call void @llvm.assume(i1 [[TMP0]])
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds i8, ptr [[Y:%.*]], i64 12
+; CHECK-NEXT:    [[TMP1:%.*]] = call ptr @fn_nonnull_noundef_arg(ptr [[GEP]])
 ; CHECK-NEXT:    ret void
 ;
 entry:
@@ -463,12 +464,13 @@
 }
 
 
-define void @test9_gep_inbouds_unknown_null(i1 %X, ptr %Y, i64 %I) {
-; CHECK-LABEL: @test9_gep_inbouds_unknown_null(
+define void @test9_gep_inbounds_unknown_null(i1 %X, ptr %Y, i64 %I) {
+; CHECK-LABEL: @test9_gep_inbounds_unknown_null(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[SPEC_SELECT:%.*]] = select i1 [[X:%.*]], ptr null, ptr [[Y:%.*]]
-; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds i8, ptr [[SPEC_SELECT]], i64 [[I:%.*]]
-; CHECK-NEXT:    [[TMP0:%.*]] = call ptr @fn_nonnull_noundef_arg(ptr [[GEP]])
+; CHECK-NEXT:    [[TMP0:%.*]] = xor i1 [[X:%.*]], true
+; CHECK-NEXT:    call void @llvm.assume(i1 [[TMP0]])
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds i8, ptr [[Y:%.*]], i64 [[I:%.*]]
+; CHECK-NEXT:    [[TMP1:%.*]] = call ptr @fn_nonnull_noundef_arg(ptr [[GEP]])
 ; CHECK-NEXT:    ret void
 ;
 entry:
Index: llvm/lib/Transforms/Utils/SimplifyCFG.cpp
===================================================================
--- llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -7121,7 +7121,12 @@
     // Look through GEPs. A load from a GEP derived from NULL is still undefined
     if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Use))
       if (GEP->getPointerOperand() == I) {
-        if (!GEP->isInBounds() || !GEP->hasAllZeroIndices())
+        // The current base address is null, there are four scenarios to consider:
+        // getelementptr (TY, null, 0)                 -> null
+        // getelementptr (TY, null, not zero)          -> maybe be modified
+        // getelementptr inbounds (TY, null, 0)        -> null
+        // getelementptr inbounds (TY, null, not zero) -> poison
+        if (!GEP->isInBounds() && !GEP->hasAllZeroIndices())
           PtrValueMayBeModified = true;
         return passingValueIsAlwaysUndefined(V, GEP, PtrValueMayBeModified);
       }


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