Support zero size types in StackSafetyAnalysis.

eugenis · eugenis · commit 34ab56904e30 · 2020-01-27T15:22:59.000-08:00
Reviewers: vitalybuka Subscribers: hiraditya, llvm-commits Tags: #llvm Differential Revision: https://reviews.llvm.org/D73395
diff --git a/llvm/lib/Analysis/StackSafetyAnalysis.cpp b/llvm/lib/Analysis/StackSafetyAnalysis.cpp
@@ -252,6 +252,10 @@ StackSafetyLocalAnalysis::offsetFromAlloca(Value *Addr,
 ConstantRange
 StackSafetyLocalAnalysis::getAccessRange(Value *Addr, const Value *AllocaPtr,
                                          ConstantRange SizeRange) {
+  // Zero-size loads and stores do not access memory.
+  if (SizeRange.isEmptySet())
+    return ConstantRange::getEmpty(PointerSize);
+
   if (!SE.isSCEVable(Addr->getType()))
     return UnknownRange;
 
diff --git a/llvm/test/Analysis/StackSafetyAnalysis/local.ll b/llvm/test/Analysis/StackSafetyAnalysis/local.ll
@@ -368,3 +368,20 @@ entry:
   store <vscale x 4 x i32> %v, <vscale x 4 x i32>* %p, align 4
   ret void
 }
+
+%zerosize_type = type {}
+
+define void @ZeroSize(%zerosize_type *%p)  {
+; CHECK-LABEL: @ZeroSize dso_preemptable{{$}}
+; CHECK-NEXT: args uses:
+; CHECK-NEXT:   p[]: empty-set
+; CHECK-NEXT: allocas uses:
+; CHECK-NEXT:   x[0]: empty-set
+; CHECK-NOT: ]:
+entry:
+  %x = alloca %zerosize_type, align 4
+  store %zerosize_type undef, %zerosize_type* %x, align 4
+  store %zerosize_type undef, %zerosize_type* undef, align 4
+  %val = load %zerosize_type, %zerosize_type* %p, align 4
+  ret void
+}
