Bug fix: use dyn_cast_or_null instead of dyn_cast

[• hulx2000]

Summary

My earlier patch failed to check null ptr before dyn_cast.

[arsenm]

You could also use dyn_cast_or_null

[mcrosier]

lib/Transforms/Scalar/SeparateConstOffsetFromGEP.cpp

828 ↗

(On Diff #47676)

You might consider using dyn_cast_or_null(), so you can reduce indent and fold the null checks into the inner if condition.

test/CodeGen/AArch64/gep-nullptr.ll

6 ↗

(On Diff #47676)

Can you please simplify some of the names, so this is more human readable?

29 ↗

(On Diff #47676)

Please drop the attribute/metadata if it's not relevant to reproducing the issue.

[mcrosier]

lib/Transforms/Scalar/SeparateConstOffsetFromGEP.cpp

829 ↗

(On Diff #47850)

I believe you still need to add the nullptr checks for FirstGEP and SecondGEP.

[• hulx2000]

lib/Transforms/Scalar/SeparateConstOffsetFromGEP.cpp

829 ↗

(On Diff #47853)

Thanks, Chad:

That's not needed because I checked in isLegalToSwapOperand().

[mcrosier]

Can you please cleanup the test case to be more human readable?

Is the test just verifying that we don't get a compiler ICE due to dereferencing a nullptr? If so, please add a comment to the test case expressing this.

lib/Transforms/Scalar/SeparateConstOffsetFromGEP.cpp

829 ↗

(On Diff #47853)

Okay, that's fine.

test/CodeGen/AArch64/gep-nullptr.ll

10 ↗

(On Diff #47853)

Is the lifetime intrinsic relevant to the test?

17 ↗

(On Diff #47853)

You should probably use a CHECK-LABEL directive like

; CHECK-LABEL: test

[mehdi_amini]

test/CodeGen/AArch64/gep-nullptr.ll

2 ↗

(On Diff #47853)

Why is an assert build required?

[mcrosier]

LGTM.

llvm/trunk/lib/Transforms/Scalar/SeparateConstOffsetFromGEP.cpp

if (AccumulativeByteOffset != 0) {
     ResultPtr =
         Builder.CreateGEP(Builder.getInt8Ty(), ResultPtr, Offset, "uglygep");
   } else
     isSwapCandidate = false;
 
   // If we created a GEP with constant index, and the base is loop invariant,
   // then we swap the first one with it, so LICM can move constant GEP out
   // later.
-  GetElementPtrInst *FirstGEP = dyn_cast<GetElementPtrInst>(FirstResult);
-  GetElementPtrInst *SecondGEP = dyn_cast<GetElementPtrInst>(ResultPtr);
+  GetElementPtrInst *FirstGEP = dyn_cast_or_null<GetElementPtrInst>(FirstResult);
+  GetElementPtrInst *SecondGEP = dyn_cast_or_null<GetElementPtrInst>(ResultPtr);
   if (isSwapCandidate && isLegalToSwapOperand(FirstGEP, SecondGEP, L))
     swapGEPOperand(FirstGEP, SecondGEP);
 
   if (ResultPtr->getType() != Variadic->getType())
     ResultPtr = Builder.CreateBitCast(ResultPtr, Variadic->getType());
 
   Variadic->replaceAllUsesWith(ResultPtr);
   Variadic->eraseFromParent();

llvm/trunk/test/CodeGen/AArch64/gep-nullptr.ll

+; RUN: llc -O3 -aarch64-gep-opt=true   < %s |FileCheck %s
+target datalayout = "e-m:e-i64:64-i128:128-n8:16:32:64-S128"
+target triple = "aarch64--linux-gnu"
+
+%structA = type { i8, i8, i8, i8, i8, i8, [4 x i8], i8, i8, [2 x i32], [2 x %unionMV], [4 x [2 x %unionMV]], [4 x [2 x %unionMV]], [4 x i8], i8*, i8*, i32, i8* }
+%unionMV = type { i32 }
+
+; Function Attrs: nounwind
+define void @test(%structA* %mi_block) {
+entry:
+  br i1 undef, label %for.body13.us, label %if.else
+
+; Just make sure we don't get a compiler ICE due to dereferncing a nullptr.
+; CHECK-LABEL: test
+for.body13.us:                                    ; preds = %entry
+  %indvars.iv.next40 = or i64 0, 1
+  %packed4.i.us.1 = getelementptr inbounds %structA, %structA* %mi_block, i64 0, i32 11, i64 0, i64 %indvars.iv.next40, i32 0
+  unreachable
+
+if.else:                                          ; preds = %entry
+  ret void
+}
+