Revert 75571; I'm convinced this isn't the right thing to do.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@75642 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 8 insertions, 28 deletions

diff --git a/lib/Transforms/Scalar/SimplifyCFGPass.cpp b/lib/Transforms/Scalar/SimplifyCFGPass.cpp
index 155d5d81e3..f6cffdd0ef 100644
--- a/lib/Transforms/Scalar/SimplifyCFGPass.cpp
+++ b/lib/Transforms/Scalar/SimplifyCFGPass.cpp
@@ -109,8 +109,6 @@ static bool MarkAliveBlocks(BasicBlock *BB,
     if (!Reachable.insert(BB))
       continue;
 
-    bool AsmFound = false;
-    StoreInst *UndefStore = 0;
     // Do a quick scan of the basic block, turning any obviously unreachable
     // instructions into LLVM unreachable insts.  The instruction combining pass
     // canonicalizes unreachable insts into stores to null or undef.
@@ -127,27 +125,20 @@ static bool MarkAliveBlocks(BasicBlock *BB,
           }
           break;
         }
-        if (isa<InlineAsm>(CI->getOperand(0)))
-          AsmFound = true;
       }
       
       if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) {
         Value *Ptr = SI->getOperand(1);
-
-        if ((isa<UndefValue>(Ptr) ||
-             (isa<ConstantPointerNull>(Ptr) &&
-              cast<PointerType>(Ptr->getType())->getAddressSpace() == 0)) &&
-            !UndefStore)
-          UndefStore = SI;
+        
+        if (isa<UndefValue>(Ptr) ||
+            (isa<ConstantPointerNull>(Ptr) &&
+             cast<PointerType>(Ptr->getType())->getAddressSpace() == 0)) {
+          ChangeToUnreachable(SI, Context);
+          Changed = true;
+          break;
+        }
       }
     }
-    // We can't delete asm's just because their inputs are undefined;
-    // xor R, R is a common idiom for zeroing a register, for example.
-    // Assume user knows what he is doing.
-    if (UndefStore && !AsmFound) {
-      ChangeToUnreachable(UndefStore, Context);
-      Changed = true;
-    }
 
     // Turn invokes that call 'nounwind' functions into ordinary calls.
     if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator()))
diff --git a/test/Transforms/SimplifyCFG/2009-07-13-no-delete-asm.ll b/test/Transforms/SimplifyCFG/2009-07-13-no-delete-asm.ll
deleted file mode 100644
index 4664ee0348..0000000000
--- a/test/Transforms/SimplifyCFG/2009-07-13-no-delete-asm.ll
+++ /dev/null
@@ -1,11 +0,0 @@
-; RUN: llvm-as < %s | opt -simplifycfg | llvm-dis | grep xor
-; ModuleID = '<stdin>'
-target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128"
-target triple = "i386-apple-darwin9.6"
-
-define void @bar() nounwind {
-entry:
-	store i16 undef, i16* null
-	%asmtmp = call i32 asm sideeffect "xor $0, $0", "=={bx},rm,~{dirflag},~{fpsr},~{flags},~{memory}"(i16 undef) nounwind		; <i32> [#uses=0]
-	ret void
-}