[PATCH] Move recursive GlobalAlias handling to be after the max depth check in computeKnownBits()

[Michael Kuperstein]

Hi chandlerc, majnemer,

r220165 moves GlobalAlias handling to be before GlobalValue handling, otherwise it's dead code. Unfortunately, that also moved it to be before the max depth check, causing an assert. 
Moved it forward to where it's safe, and changed the GlobalValue handling to only look at GlobalObjects.

Sorry for the awful test-case, this is bugpoint-reduced C++ with a bit of manual clean-up. I can try to clean it up more, if necessary.

http://reviews.llvm.org/D6758

Files:
  lib/Analysis/ValueTracking.cpp
  test/Transforms/InstCombine/alias-recursion.ll

Index: lib/Analysis/ValueTracking.cpp
===================================================================
--- lib/Analysis/ValueTracking.cpp
+++ lib/Analysis/ValueTracking.cpp
@@ -793,22 +793,11 @@
     return;
   }
 
-  // A weak GlobalAlias is totally unknown. A non-weak GlobalAlias has
-  // the bits of its aliasee.
-  if (GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) {
-    if (GA->mayBeOverridden()) {
-      KnownZero.clearAllBits(); KnownOne.clearAllBits();
-    } else {
-      computeKnownBits(GA->getAliasee(), KnownZero, KnownOne, TD, Depth+1, Q);
-    }
-    return;
-  }
-
   // The address of an aligned GlobalValue has trailing zeros.
-  if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
-    unsigned Align = GV->getAlignment();
+  if (GlobalObject *GO = dyn_cast<GlobalObject>(V)) {
+    unsigned Align = GO->getAlignment();
     if (Align == 0 && TD) {
-      if (GlobalVariable *GVar = dyn_cast<GlobalVariable>(GV)) {
+      if (GlobalVariable *GVar = dyn_cast<GlobalVariable>(GO)) {
         Type *ObjectType = GVar->getType()->getElementType();
         if (ObjectType->isSized()) {
           // If the object is defined in the current Module, we'll be giving
@@ -855,6 +844,17 @@
   if (Depth == MaxDepth)
     return;  // Limit search depth.
 
+  // A weak GlobalAlias is totally unknown. A non-weak GlobalAlias has
+  // the bits of its aliasee.
+  if (GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) {
+    if (GA->mayBeOverridden()) {
+      KnownZero.clearAllBits(); KnownOne.clearAllBits();
+    } else {
+      computeKnownBits(GA->getAliasee(), KnownZero, KnownOne, TD, Depth+1, Q);
+    }
+    return;
+  }
+
   // Check whether a nearby assume intrinsic can determine some known bits.
   computeKnownBitsFromAssume(V, KnownZero, KnownOne, TD, Depth, Q);
 
Index: test/Transforms/InstCombine/alias-recursion.ll
===================================================================
--- test/Transforms/InstCombine/alias-recursion.ll
+++ test/Transforms/InstCombine/alias-recursion.ll
@@ -0,0 +1,45 @@
+; RUN: opt < %s -instcombine -S | FileCheck %s
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-windows-msvc"
+
+%rtti.CompleteObjectLocator = type { i32, i32, i32, i32, i32, i32 }
+%rtti.TypeDescriptor = type { i8**, i8*, [8 x i8] }
+%rtti.ClassHierarchyDescriptor = type { i32, i32, i32, i32 }
+%rtti.BaseClassDescriptor = type { i32, i32, i32, i32, i32, i32, i32 }
+%class.A = type { i32 (...)** }
+
+ at 0 = private unnamed_addr constant [2 x i8*] [i8* bitcast (%rtti.CompleteObjectLocator* @"\01??_R4A@@6B@" to i8*), i8* bitcast (i32 (%class.A*)* @"\01?virt at A@@UEAAHXZ" to i8*)]
+@"\01??_R4A@@6B@" = linkonce_odr constant %rtti.CompleteObjectLocator { i32 1, i32 0, i32 0, i32 trunc (i64 sub nuw nsw (i64 ptrtoint (%rtti.TypeDescriptor* @"\01??_R0?AVA@@@8" to i64), i64 ptrtoint (i8* @__ImageBase to i64)) to i32), i32 trunc (i64 sub nuw nsw (i64 ptrtoint (%rtti.ClassHierarchyDescriptor* @"\01??_R3A@@8" to i64), i64 ptrtoint (i8* @__ImageBase to i64)) to i32), i32 trunc (i64 sub nuw nsw (i64 ptrtoint (%rtti.CompleteObjectLocator* @"\01??_R4A@@6B@" to i64), i64 ptrtoint (i8* @__ImageBase to i64)) to i32) }
+@"\01??_7type_info@@6B@" = external constant i8*
+@"\01??_R0?AVA@@@8" = linkonce_odr global %rtti.TypeDescriptor { i8** @"\01??_7type_info@@6B@", i8* null, [8 x i8] c".?AVA@@\00" }
+ at __ImageBase = external constant i8
+@"\01??_R3A@@8" = linkonce_odr constant %rtti.ClassHierarchyDescriptor { i32 0, i32 0, i32 1, i32 trunc (i64 sub nuw nsw (i64 ptrtoint ([2 x i32]* @"\01??_R2A@@8" to i64), i64 ptrtoint (i8* @__ImageBase to i64)) to i32) }
+@"\01??_R2A@@8" = linkonce_odr constant [2 x i32] [i32 trunc (i64 sub nuw nsw (i64 ptrtoint (%rtti.BaseClassDescriptor* @"\01??_R1A@?0A at EA@A@@8" to i64), i64 ptrtoint (i8* @__ImageBase to i64)) to i32), i32 0]
+@"\01??_R1A@?0A at EA@A@@8" = linkonce_odr constant %rtti.BaseClassDescriptor { i32 trunc (i64 sub nuw nsw (i64 ptrtoint (%rtti.TypeDescriptor* @"\01??_R0?AVA@@@8" to i64), i64 ptrtoint (i8* @__ImageBase to i64)) to i32), i32 0, i32 0, i32 -1, i32 0, i32 64, i32 trunc (i64 sub nuw nsw (i64 ptrtoint (%rtti.ClassHierarchyDescriptor* @"\01??_R3A@@8" to i64), i64 ptrtoint (i8* @__ImageBase to i64)) to i32) }
+@"\01??_7A@@6B@" = unnamed_addr alias getelementptr inbounds ([2 x i8*]* @0, i32 0, i32 1)
+
+define void @test() {
+; CHECK-LABEL: test
+entry:
+  br i1 undef, label %for.body.lr.ph, label %for.end
+
+for.body.lr.ph:                                   ; preds = %entry
+  br label %for.body
+
+for.body:                                         ; preds = %for.body.for.body_crit_edge, %for.body.lr.ph
+  %vtable = phi i32 (%class.A*)** [ bitcast (i8** @"\01??_7A@@6B@" to i32 (%class.A*)**), %for.body.lr.ph ], [ null, %for.body.for.body_crit_edge ]
+  %0 = load i32 (%class.A*)** %vtable, align 8
+  %call2 = tail call i32 %0(%class.A* undef)
+  br i1 undef, label %for.body.for.body_crit_edge, label %for.end
+
+for.body.for.body_crit_edge:                      ; preds = %for.body
+  br label %for.body
+
+for.end:                                          ; preds = %for.body, %entry
+  ret void
+}
+
+declare i32 @"\01?virt at A@@UEAAHXZ"(%class.A*) unnamed_addr align 2
+
+

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