PR9634: Don't unconditionally tell the AliasSetTracker that the PreheaderLoad

is equivalent to any other relevant value; it isn't true in general.
If it is equivalent, the LoopPromoter will tell the AST the equivalence.
Also, delete the PreheaderLoad if it is unused.

Chris, since you were the last one to make major changes here, can you check
that this is sane?

llvm-svn: 129049

4 files changed, 45 insertions, 23 deletions

diff --git a/llvm/lib/Transforms/Scalar/LICM.cpp b/llvm/lib/Transforms/Scalar/LICM.cpp
index 6cf1bd3deb5..93de9cf002e 100644
--- a/llvm/lib/Transforms/Scalar/LICM.cpp
+++ b/llvm/lib/Transforms/Scalar/LICM.cpp
@@ -743,30 +743,13 @@ void LICM::PromoteAliasSet(AliasSet &AS) {
                  Preheader->getTerminator());
   SSA.AddAvailableValue(Preheader, PreheaderLoad);
 
-  // Copy any value stored to or loaded from a must-alias of the pointer.
-  if (PreheaderLoad->getType()->isPointerTy()) {
-    Value *SomeValue;
-    if (LoadInst *LI = dyn_cast<LoadInst>(LoopUses[0]))
-      SomeValue = LI;
-    else
-      SomeValue = cast<StoreInst>(LoopUses[0])->getValueOperand();
-    
-    CurAST->copyValue(SomeValue, PreheaderLoad);
-  }
-
   // Rewrite all the loads in the loop and remember all the definitions from
   // stores in the loop.
   Promoter.run(LoopUses);
-  
-  // If the preheader load is itself a pointer, we need to tell alias analysis
-  // about the new pointer we created in the preheader block and about any PHI
-  // nodes that just got inserted.
-  if (PreheaderLoad->getType()->isPointerTy()) {
-    for (unsigned i = 0, e = NewPHIs.size(); i != e; ++i)
-      CurAST->copyValue(PreheaderLoad, NewPHIs[i]);
-  }
-  
-  // fwew, we're done!
+
+  // If the SSAUpdater didn't use the load in the preheader, just zap it now.
+  if (PreheaderLoad->use_empty())
+    PreheaderLoad->eraseFromParent();
 }
 
 
diff --git a/llvm/test/Analysis/BasicAA/store-promote.ll b/llvm/test/Analysis/BasicAA/store-promote.ll
index 33d0f3a5449..0db805c3e21 100644
--- a/llvm/test/Analysis/BasicAA/store-promote.ll
+++ b/llvm/test/Analysis/BasicAA/store-promote.ll
@@ -24,7 +24,7 @@ Out:            ; preds = %Loop
         
 ; The Loop block should be empty after the load/store are promoted.
 ; CHECK:     @test1
-; CHECK:        load i32* @B
+; CHECK:        load i32* @A
 ; CHECK:      Loop:
 ; CHECK-NEXT:   br i1 %c, label %Out, label %Loop
 ; CHECK:      Out:
diff --git a/llvm/test/Transforms/LICM/2007-10-01-PromoteSafeValue.ll b/llvm/test/Transforms/LICM/2007-10-01-PromoteSafeValue.ll
index 59f1dcbe2d7..e3d0d02edd9 100644
--- a/llvm/test/Transforms/LICM/2007-10-01-PromoteSafeValue.ll
+++ b/llvm/test/Transforms/LICM/2007-10-01-PromoteSafeValue.ll
@@ -1,4 +1,4 @@
-; RUN: opt < %s -licm -S | grep promoted
+; RUN: opt < %s -licm -S | FileCheck %s
 ; Promote value if at least one use is safe
 
 
@@ -15,6 +15,8 @@ cond.true:              ; preds = %loop.head
         store i32 40, i32* %p
         br label %loop.head
 
+; CHECK: exit:
+; CHECK: store i32 20, i32* %p
 exit:           ; preds = %loop.head
         ret i32 0
 }
diff --git a/llvm/test/Transforms/LICM/2011-04-06-PromoteResultOfPromotion.ll b/llvm/test/Transforms/LICM/2011-04-06-PromoteResultOfPromotion.ll
new file mode 100644
index 00000000000..86c2679b076
--- /dev/null
+++ b/llvm/test/Transforms/LICM/2011-04-06-PromoteResultOfPromotion.ll
@@ -0,0 +1,37 @@
+; RUN: opt < %s -tbaa -licm -S | FileCheck %s
+; PR9634
+
+@g_58 = common global i32 0, align 4
+@g_116 = common global i32* null, align 8
+
+define void @f() nounwind {
+
+; CHECK: entry:
+; CHECK: alloca [9 x i16]
+; CHECK: load i32* @g_58
+; CHECK: br label %for.body
+
+entry:
+  %l_87.i = alloca [9 x i16], align 16
+  br label %for.body
+
+for.body:                                         ; preds = %entry, %for.inc
+  %inc12 = phi i32 [ 0, %entry ], [ %inc, %for.body ]
+  store i32* @g_58, i32** @g_116, align 8, !tbaa !0
+  %tmp2 = load i32** @g_116, align 8, !tbaa !0
+  %tmp3 = load i32* %tmp2, !tbaa !4
+  %or = or i32 %tmp3, 10
+  store i32 %or, i32* %tmp2, !tbaa !4
+  %inc = add nsw i32 %inc12, 1
+  %cmp = icmp slt i32 %inc, 4
+  br i1 %cmp, label %for.body, label %for.end
+
+for.end:                                          ; preds = %for.inc
+  ret void
+}
+
+!0 = metadata !{metadata !"any pointer", metadata !1}
+!1 = metadata !{metadata !"omnipotent char", metadata !2}
+!2 = metadata !{metadata !"Simple C/C++ TBAA", null}
+!3 = metadata !{metadata !"short", metadata !1}
+!4 = metadata !{metadata !"int", metadata !1}