Make DecomposeGEPExpression check SimplifyInstruction only

after checking for a GEP, so that it matches what GetUnderlyingObject
does. This fixes an obscure bug turned up by bugpoint in the testcase
for PR9931.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@131971 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 37 insertions, 9 deletions

diff --git a/lib/Analysis/BasicAliasAnalysis.cpp b/lib/Analysis/BasicAliasAnalysis.cpp
index 989d8e0..03785fd 100644
--- a/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/lib/Analysis/BasicAliasAnalysis.cpp
@@ -281,17 +281,20 @@ DecomposeGEPExpression(const Value *V, int64_t &BaseOffs,
       continue;
     }
 
-    if (const Instruction *I = dyn_cast<Instruction>(V))
-      // TODO: Get a DominatorTree and use it here.
-      if (const Value *Simplified =
-            SimplifyInstruction(const_cast<Instruction *>(I), TD)) {
-        V = Simplified;
-        continue;
-      }
-    
     const GEPOperator *GEPOp = dyn_cast<GEPOperator>(Op);
-    if (GEPOp == 0)
+    if (GEPOp == 0) {
+      // If it's not a GEP, hand it off to SimplifyInstruction to see if it
+      // can come up with something. This matches what GetUnderlyingObject does.
+      if (const Instruction *I = dyn_cast<Instruction>(V))
+        // TODO: Get a DominatorTree and use it here.
+        if (const Value *Simplified =
+              SimplifyInstruction(const_cast<Instruction *>(I), TD)) {
+          V = Simplified;
+          continue;
+        }
+    
       return V;
+    }
     
     // Don't attempt to analyze GEPs over unsized objects.
     if (!cast<PointerType>(GEPOp->getOperand(0)->getType())
diff --git a/test/Analysis/BasicAA/underlying-value.ll b/test/Analysis/BasicAA/underlying-value.ll
new file mode 100644
index 0000000..0671c82
--- /dev/null
+++ b/test/Analysis/BasicAA/underlying-value.ll
@@ -0,0 +1,25 @@
+; RUN: opt -basicaa -licm -S < %s
+; PR9931
+
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
+
+define void @func_20() nounwind {
+entry:
+  br label %for.cond
+
+for.cond:                                         ; preds = %for.cond2, %entry
+  br i1 undef, label %for.cond2, label %for.end22
+
+for.cond2:                                        ; preds = %for.body5, %for.cond
+  br i1 false, label %for.body5, label %for.cond
+
+for.body5:                                        ; preds = %for.cond2
+  %arrayidx = getelementptr inbounds [2 x i64]* undef, i32 0, i64 0
+  %tmp7 = load i64* %arrayidx, align 8
+  %arrayidx9 = getelementptr inbounds [2 x i64]* undef, i32 0, i64 undef
+  %tmp10 = load i64* %arrayidx9, align 8
+  br label %for.cond2
+
+for.end22:                                        ; preds = %for.cond
+  ret void
+}