[llvm-commits] [llvm] r145367 - in /llvm/trunk: lib/Analysis/ScalarEvolution.cpp lib/Transforms/Scalar/IndVarSimplify.cpp test/Analysis/ScalarEvolution/nsw.ll

[Andrew Trick]

Author: atrick
Date: Mon Nov 28 20:16:38 2011
New Revision: 145367

URL: http://llvm.org/viewvc/llvm-project?rev=145367&view=rev
Log:
SCEV fix. In general, Add/Mul expressions should not inherit NSW/NUW.

This reverts r139450, fixes r139453, and adds much needed comments and a
unit test.

Modified:
    llvm/trunk/lib/Analysis/ScalarEvolution.cpp
    llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp
    llvm/trunk/test/Analysis/ScalarEvolution/nsw.ll

Modified: llvm/trunk/lib/Analysis/ScalarEvolution.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ScalarEvolution.cpp?rev=145367&r1=145366&r2=145367&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ScalarEvolution.cpp (original)
+++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp Mon Nov 28 20:16:38 2011
@@ -3592,6 +3592,12 @@
     // because it leads to N-1 getAddExpr calls for N ultimate operands.
     // Instead, gather up all the operands and make a single getAddExpr call.
     // LLVM IR canonical form means we need only traverse the left operands.
+    //
+    // Don't apply this instruction's NSW or NUW flags to the new
+    // expression. The instruction may be guarded by control flow that the
+    // no-wrap behavior depends on. Non-control-equivalent instructions can be
+    // mapped to the same SCEV expression, and it would be incorrect to transfer
+    // NSW/NUW semantics to those operations.
     SmallVector<const SCEV *, 4> AddOps;
     AddOps.push_back(getSCEV(U->getOperand(1)));
     for (Value *Op = U->getOperand(0); ; Op = U->getOperand(0)) {
@@ -3606,16 +3612,10 @@
         AddOps.push_back(Op1);
     }
     AddOps.push_back(getSCEV(U->getOperand(0)));
-    SCEV::NoWrapFlags Flags = SCEV::FlagAnyWrap;
-    OverflowingBinaryOperator *OBO = cast<OverflowingBinaryOperator>(V);
-    if (OBO->hasNoSignedWrap())
-      Flags = setFlags(Flags, SCEV::FlagNSW);
-    if (OBO->hasNoUnsignedWrap())
-      Flags = setFlags(Flags, SCEV::FlagNUW);
-    return getAddExpr(AddOps, Flags);
+    return getAddExpr(AddOps);
   }
   case Instruction::Mul: {
-    // See the Add code above.
+    // Don't transfer NSW/NUW for the same reason as AddExpr.
     SmallVector<const SCEV *, 4> MulOps;
     MulOps.push_back(getSCEV(U->getOperand(1)));
     for (Value *Op = U->getOperand(0);

Modified: llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp?rev=145367&r1=145366&r2=145367&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp Mon Nov 28 20:16:38 2011
@@ -944,9 +944,13 @@
   else
     return 0;
 
+  // When creating this AddExpr, don't apply the current operations NSW or NUW
+  // flags. This instruction may be guarded by control flow that the no-wrap
+  // behavior depends on. Non-control-equivalent instructions can be mapped to
+  // the same SCEV expression, and it would be incorrect to transfer NSW/NUW
+  // semantics to those operations.
   const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(
-    SE->getAddExpr(SE->getSCEV(DU.WideDef), ExtendOperExpr,
-                   IsSigned ? SCEV::FlagNSW : SCEV::FlagNUW));
+    SE->getAddExpr(SE->getSCEV(DU.WideDef), ExtendOperExpr));
 
   if (!AddRec || AddRec->getLoop() != L)
     return 0;

Modified: llvm/trunk/test/Analysis/ScalarEvolution/nsw.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/ScalarEvolution/nsw.ll?rev=145367&r1=145366&r2=145367&view=diff
==============================================================================
--- llvm/trunk/test/Analysis/ScalarEvolution/nsw.ll (original)
+++ llvm/trunk/test/Analysis/ScalarEvolution/nsw.ll Mon Nov 28 20:16:38 2011
@@ -103,4 +103,22 @@
 ; CHECK: Loop %for.body.i.i: max backedge-taken count is ((-4 + (-1 * %begin) + %end) /u 4)
 _ZSt4fillIPiiEvT_S1_RKT0_.exit:                   ; preds = %for.body.i.i, %entry
   ret void
-}
\ No newline at end of file
+}
+
+; A single AddExpr exists for (%a + %b), which is not always <nsw>.
+; CHECK: @addnsw
+; CHECK-NOT: --> (%a + %b)<nsw>
+define i32 @addnsw(i32 %a, i32 %b) nounwind ssp {
+entry:
+  %tmp = add i32 %a, %b
+  %cmp = icmp sgt i32 %tmp, 0
+  br i1 %cmp, label %greater, label %exit
+
+greater:
+  %tmp2 = add nsw i32 %a, %b
+  br label %exit
+
+exit:
+  %result = phi i32 [ %a, %entry ], [ %tmp2, %greater ]
+  ret i32 %result
+}