[llvm] r218867 - [BUG][INDVAR] Fix for PR21014: wrong SCEV operands commuting for non-commutative instructions

[Zinovy Nis]

Author: zinovy.nis
Date: Thu Oct  2 08:01:15 2014
New Revision: 218867

URL: http://llvm.org/viewvc/llvm-project?rev=218867&view=rev
Log:
[BUG][INDVAR] Fix for PR21014: wrong SCEV operands commuting for non-commutative instructions

My commit rL216160 introduced a bug PR21014: IndVars widens code 'for (i = ; i < ...; i++) arr[ CONST - i]' into 'for (i = ; i < ...; i++) arr[ i - CONST]'
thus inverting index expression. This patch fixes it. 
Thanks to Jörg Sonnenberger for pointing.

Differential Revision: http://reviews.llvm.org/D5576


Modified:
    llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp
    llvm/trunk/test/Transforms/IndVarSimplify/2011-09-10-widen-nsw.ll

Modified: llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp?rev=218867&r1=218866&r2=218867&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp Thu Oct  2 08:01:15 2014
@@ -865,7 +865,8 @@ const SCEVAddRecExpr* WidenIV::GetExtend
 
   // One operand (NarrowDef) has already been extended to WideDef. Now determine
   // if extending the other will lead to a recurrence.
-  unsigned ExtendOperIdx = DU.NarrowUse->getOperand(0) == DU.NarrowDef ? 1 : 0;
+  const unsigned ExtendOperIdx =
+      DU.NarrowUse->getOperand(0) == DU.NarrowDef ? 1 : 0;
   assert(DU.NarrowUse->getOperand(1-ExtendOperIdx) == DU.NarrowDef && "bad DU");
 
   const SCEV *ExtendOperExpr = nullptr;
@@ -885,8 +886,16 @@ const SCEVAddRecExpr* WidenIV::GetExtend
   // 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>(
-      GetSCEVByOpCode(SE->getSCEV(DU.WideDef), ExtendOperExpr, OpCode));
+  const SCEV *lhs = SE->getSCEV(DU.WideDef);
+  const SCEV *rhs = ExtendOperExpr;
+
+  // Let's swap operands to the initial order for the case of non-commutative
+  // operations, like SUB. See PR21014.
+  if (ExtendOperIdx == 0)
+    std::swap(lhs, rhs);
+  const SCEVAddRecExpr *AddRec =
+      dyn_cast<SCEVAddRecExpr>(GetSCEVByOpCode(lhs, rhs, OpCode));
+
   if (!AddRec || AddRec->getLoop() != L)
     return nullptr;
   return AddRec;

Modified: llvm/trunk/test/Transforms/IndVarSimplify/2011-09-10-widen-nsw.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/IndVarSimplify/2011-09-10-widen-nsw.ll?rev=218867&r1=218866&r2=218867&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/IndVarSimplify/2011-09-10-widen-nsw.ll (original)
+++ llvm/trunk/test/Transforms/IndVarSimplify/2011-09-10-widen-nsw.ll Thu Oct  2 08:01:15 2014
@@ -19,7 +19,8 @@ for.body153:
 
 ; CHECK: add nsw i64 %indvars.iv, 1
 ; CHECK: sub nsw i64 %indvars.iv, 2
-; CHECK: mul nsw i64 %indvars.iv, 4
+; CHECK: sub nsw i64 4, %indvars.iv
+; CHECK: mul nsw i64 %indvars.iv, 8
 for.body170:                                      ; preds = %for.body170, %for.body153
   %i2.19 = phi i32 [ %add249, %for.body170 ], [ 0, %for.body153 ]
 
@@ -29,7 +30,10 @@ for.body170:
   %sub = sub nsw i32 %i2.19, 2
   %sub.idxprom = sext i32 %sub to i64
 
-  %mul = mul nsw i32 %i2.19, 4
+  %sub.neg = sub nsw i32 4, %i2.19
+  %sub.neg.idxprom = sext i32 %sub.neg to i64
+
+  %mul = mul nsw i32 %i2.19, 8
   %mul.idxprom = sext i32 %mul to i64
 
   %add249 = add nsw i32 %i2.19, %shl132