IR: Don't add inbounds to GEPs of extern_weak variables

Global variables that have `extern_weak` linkage may be null, so it's
incorrect to add `inbounds` when constant folding.

This also fixes a bug when parsing global aliases, whose forward
reference placeholders are global variables with `extern_weak` linkage.
If GEPs to these aliases are encountered before the alias itself, the
GEPs would incorrectly gain the `inbounds` keyword as well.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@215803 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/IR/ConstantFold.cpp b/lib/IR/ConstantFold.cpp
index 395ac3907bafd895f1feb2d4e583091596a54353..9124c1119357979bc5f8a34ec5935525bcf0311e 100644 (file)
--- a/lib/IR/ConstantFold.cpp
+++ b/lib/IR/ConstantFold.cpp
@@ -2144,9 +2144,10 @@ static Constant *ConstantFoldGetElementPtrImpl(Constant *C,
 
   // If all indices are known integers and normalized, we can do a simple
   // check for the "inbounds" property.
-  if (!Unknown && !inBounds &&
-      isa<GlobalVariable>(C) && isInBoundsIndices(Idxs))
-    return ConstantExpr::getInBoundsGetElementPtr(C, Idxs);
+  if (!Unknown && !inBounds)
+    if (auto *GV = dyn_cast<GlobalVariable>(C))
+      if (!GV->hasExternalWeakLinkage() && isInBoundsIndices(Idxs))
+        return ConstantExpr::getInBoundsGetElementPtr(C, Idxs);
 
   return nullptr;
 }

diff --git a/test/Assembler/ConstantExprNoFold.ll b/test/Assembler/ConstantExprNoFold.ll
index d21441372bfc5b915f53de7a248e000df7868cc2..04ad3f5b130088ebfa44d1c38b295897d1772faa 100644 (file)
--- a/test/Assembler/ConstantExprNoFold.ll
+++ b/test/Assembler/ConstantExprNoFold.ll
@@ -25,3 +25,15 @@ target datalayout = "p:32:32"
 
 ; CHECK: @E = global i64 addrspace(1)* addrspacecast (i64* @A to i64 addrspace(1)*)
 @E = global i64 addrspace(1)* addrspacecast(i64* @A to i64 addrspace(1)*)
+
+; Don't add an inbounds on @weak.gep, since @weak may be null.
+; CHECK: @weak.gep = global i32* getelementptr (i32* @weak, i32 1)
+@weak.gep = global i32* getelementptr (i32* @weak, i32 1)
+@weak = extern_weak global i32
+
+; Don't add an inbounds on @glob.a3, since it's not inbounds.
+; CHECK: @glob.a3 = alias getelementptr (i32* @glob.a2, i32 1)
+@glob = global i32 0
+@glob.a3 = alias getelementptr (i32* @glob.a2, i32 1)
+@glob.a2 = alias getelementptr (i32* @glob.a1, i32 1)
+@glob.a1 = alias i32* @glob