[llvm-commits] [llvm] r160711 - in /llvm/trunk: lib/Analysis/ConstantFolding.cpp test/Transforms/InstCombine/2012-07-25-LoadPart.ll

[Duncan Sands]

Author: baldrick
Date: Wed Jul 25 04:14:54 2012
New Revision: 160711

URL: http://llvm.org/viewvc/llvm-project?rev=160711&view=rev
Log:
When folding a load from a global constant, if the load started in the middle
of an array element (rather than at the beginning of the element) and extended
into the next element, then the load from the second element was being handled
wrong due to incorrect updating of the notion of which byte to load next.  This
fixes PR13442.  Thanks to Chris Smowton for reporting the problem, analyzing it
and providing a fix.

Added:
    llvm/trunk/test/Transforms/InstCombine/2012-07-25-LoadPart.ll
Modified:
    llvm/trunk/lib/Analysis/ConstantFolding.cpp

Modified: llvm/trunk/lib/Analysis/ConstantFolding.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ConstantFolding.cpp?rev=160711&r1=160710&r2=160711&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ConstantFolding.cpp (original)
+++ llvm/trunk/lib/Analysis/ConstantFolding.cpp Wed Jul 25 04:14:54 2012
@@ -358,17 +358,20 @@
       NumElts = AT->getNumElements();
     else
       NumElts = cast<VectorType>(C->getType())->getNumElements();
-    
+
     for (; Index != NumElts; ++Index) {
       if (!ReadDataFromGlobal(C->getAggregateElement(Index), Offset, CurPtr,
                               BytesLeft, TD))
         return false;
-      if (EltSize >= BytesLeft)
+
+      uint64_t BytesWritten = EltSize - Offset;
+      assert(BytesWritten <= EltSize && "Not indexing into this element?");
+      if (BytesWritten >= BytesLeft)
         return true;
-      
+
       Offset = 0;
-      BytesLeft -= EltSize;
-      CurPtr += EltSize;
+      BytesLeft -= BytesWritten;
+      CurPtr += BytesWritten;
     }
     return true;
   }

Added: llvm/trunk/test/Transforms/InstCombine/2012-07-25-LoadPart.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/2012-07-25-LoadPart.ll?rev=160711&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/2012-07-25-LoadPart.ll (added)
+++ llvm/trunk/test/Transforms/InstCombine/2012-07-25-LoadPart.ll Wed Jul 25 04:14:54 2012
@@ -0,0 +1,12 @@
+; RUN: opt < %s -instcombine -S | FileCheck %s
+; PR13442
+
+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-f80:32:32-n8:16:32-S128"
+
+ at test = constant [4 x i32] [i32 1, i32 2, i32 3, i32 4]
+
+define i64 @foo() {
+  %ret = load i64* bitcast (i8* getelementptr (i8* bitcast ([4 x i32]* @test to i8*), i64 2) to i64*)
+  ret i64 %ret
+  ; CHECK: ret i64 844424930263040
+}