Fix regression from my recent GlobalsAA fix.

There are two fixes here: one, AnalyzeUsesOfPointer can't return
false until it has checked all the uses of the pointer. Two, if a
global uses another global, we have to assume the address of the
first global escapes.

Fixes https://llvm.org/bugs/show_bug.cgi?id=30707 .

Differential Revision: https://reviews.llvm.org/D25798

llvm-svn: 285034

Author: Eli Friedman

llvm/lib/Analysis/GlobalsModRef.cpp

@@ -367,7 +367,9 @@ bool GlobalsAAResult::AnalyzeUsesOfPointer(Value *V,
       if (!isa<ConstantPointerNull>(ICI->getOperand(1)))
         return true; // Allow comparison against null.
     } else if (Constant *C = dyn_cast<Constant>(I)) {
-      return C->isConstantUsed();
+      // Ignore constants which don't have any live uses.
+      if (isa<GlobalValue>(C) || C->isConstantUsed())
+        return true;
     } else {
       return true;
     }

llvm/test/Analysis/GlobalsModRef/global-used-by-global.ll

@@ -0,0 +1,54 @@
+; RUN: opt < %s -globals-aa -gvn -S | FileCheck %s
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+
+@a = internal global i32* null, align 8
+@b = global i32** @a, align 8
+@c = global i32** @a, align 8
+@d = common global i32 0, align 4
+
+; Make sure we globals-aa doesn't get confused and allow hoisting
+; the load from @a out of the loop.
+
+; CHECK-LABEL: define i32 @main()
+; CHECK: for.body:
+; CHECK-NEXT:   %2 = load i32**, i32*** @b, align 8
+; CHECK-NEXT:   store i32* @d, i32** %2, align 8
+; CHECK-NEXT:   %3 = load i32*, i32** @a, align 8
+; CHECK-NEXT:   %cmp1 = icmp ne i32* %3, @d
+; CHECK-NEXT:   br i1 %cmp1, label %if.then, label %if.end
+
+define i32 @main() {
+entry:
+  %0 = load i32, i32* @d, align 4
+  br label %for.cond
+
+for.cond:                                         ; preds = %if.end, %entry
+  %1 = phi i32 [ %inc, %if.end ], [ %0, %entry ]
+  %cmp = icmp slt i32 %1, 1
+  br i1 %cmp, label %for.body, label %for.end
+
+for.body:                                         ; preds = %for.cond
+  %2 = load i32**, i32*** @b, align 8
+  store i32* @d, i32** %2, align 8
+  %3 = load i32*, i32** @a, align 8
+  %cmp1 = icmp ne i32* %3, @d
+  br i1 %cmp1, label %if.then, label %if.end
+
+if.then:                                          ; preds = %for.body
+  br label %return
+
+if.end:                                           ; preds = %for.body
+  %4 = load i32, i32* @d, align 4
+  %inc = add nsw i32 %4, 1
+  store i32 %inc, i32* @d, align 4
+  br label %for.cond
+
+for.end:                                          ; preds = %for.cond
+  br label %return
+
+return:                                           ; preds = %for.end, %if.then
+  %retval.0 = phi i32 [ 1, %if.then ], [ 0, %for.end ]
+  ret i32 %retval.0
+}
+