[llvm-commits] [llvm] r99488 - in /llvm/trunk: lib/Transforms/Scalar/GVN.cpp test/Transforms/GVN/rle.ll

[Chris Lattner]

Author: lattner
Date: Thu Mar 25 00:58:19 2010
New Revision: 99488

URL: http://llvm.org/viewvc/llvm-project?rev=99488&view=rev
Log:
fix PR6642, GVN forwarding from memset to load of the base of the memset.

Modified:
    llvm/trunk/lib/Transforms/Scalar/GVN.cpp
    llvm/trunk/test/Transforms/GVN/rle.ll

Modified: llvm/trunk/lib/Transforms/Scalar/GVN.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/GVN.cpp?rev=99488&r1=99487&r2=99488&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/GVN.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/GVN.cpp Thu Mar 25 00:58:19 2010
@@ -1004,18 +1004,18 @@
   
   // If the load and store are to the exact same address, they should have been
   // a must alias.  AA must have gotten confused.
-  // FIXME: Study to see if/when this happens.
-  if (LoadOffset == StoreOffset) {
+  // FIXME: Study to see if/when this happens.  One case is forwarding a memset
+  // to a load from the base of the memset.
 #if 0
+  if (LoadOffset == StoreOffset) {
     dbgs() << "STORE/LOAD DEP WITH COMMON POINTER MISSED:\n"
     << "Base       = " << *StoreBase << "\n"
     << "Store Ptr  = " << *WritePtr << "\n"
     << "Store Offs = " << StoreOffset << "\n"
     << "Load Ptr   = " << *LoadPtr << "\n";
     abort();
-#endif
-    return -1;
   }
+#endif
   
   // If the load and store don't overlap at all, the store doesn't provide
   // anything to the load.  In this case, they really don't alias at all, AA
@@ -1031,11 +1031,11 @@
   
   
   bool isAAFailure = false;
-  if (StoreOffset < LoadOffset) {
+  if (StoreOffset < LoadOffset)
     isAAFailure = StoreOffset+int64_t(StoreSize) <= LoadOffset;
-  } else {
+  else
     isAAFailure = LoadOffset+int64_t(LoadSize) <= StoreOffset;
-  }
+
   if (isAAFailure) {
 #if 0
     dbgs() << "STORE LOAD DEP WITH COMMON BASE:\n"

Modified: llvm/trunk/test/Transforms/GVN/rle.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/GVN/rle.ll?rev=99488&r1=99487&r2=99488&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/GVN/rle.ll (original)
+++ llvm/trunk/test/Transforms/GVN/rle.ll Thu Mar 25 00:58:19 2010
@@ -531,4 +531,16 @@
 }
 
 
+; PR6642
+define i32 @memset_to_load() nounwind readnone {
+entry:
+  %x = alloca [256 x i32], align 4                ; <[256 x i32]*> [#uses=2]
+  %tmp = bitcast [256 x i32]* %x to i8*           ; <i8*> [#uses=1]
+  call void @llvm.memset.i64(i8* %tmp, i8 0, i64 1024, i32 4)
+  %arraydecay = getelementptr inbounds [256 x i32]* %x, i32 0, i32 0 ; <i32*>
+  %tmp1 = load i32* %arraydecay                   ; <i32> [#uses=1]
+  ret i32 %tmp1
+; CHECK: @memset_to_load
+; CHECK: ret i32 0
+}