[llvm-commits] [llvm] r46959 - in /llvm/trunk: lib/Analysis/ScalarEvolution.cpp test/Analysis/ScalarEvolution/2008-02-11-ReversedCondition.ll

[Wojciech Matyjewicz]

Author: wmat
Date: Mon Feb 11 12:37:34 2008
New Revision: 46959

URL: http://llvm.org/viewvc/llvm-project?rev=46959&view=rev
Log:
If the LHS of the comparison is a loop-invariant we also want to move it 
to the RHS. This simple change allows to compute loop iteration count 
for loops with condition similar to the one in the testcase (which seems 
to be quite common).

Added:
    llvm/trunk/test/Analysis/ScalarEvolution/2008-02-11-ReversedCondition.ll
Modified:
    llvm/trunk/lib/Analysis/ScalarEvolution.cpp

Modified: llvm/trunk/lib/Analysis/ScalarEvolution.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ScalarEvolution.cpp?rev=46959&r1=46958&r2=46959&view=diff

==============================================================================
--- llvm/trunk/lib/Analysis/ScalarEvolution.cpp (original)
+++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp Mon Feb 11 12:37:34 2008
@@ -1819,8 +1819,8 @@
 
   // At this point, we would like to compute how many iterations of the 
   // loop the predicate will return true for these inputs.
-  if (isa<SCEVConstant>(LHS) && !isa<SCEVConstant>(RHS)) {
-    // If there is a constant, force it into the RHS.
+  if (LHS->isLoopInvariant(L) && !RHS->isLoopInvariant(L)) {
+    // If there is a loop-invariant, force it into the RHS.
     std::swap(LHS, RHS);
     Cond = ICmpInst::getSwappedPredicate(Cond);
   }

Added: llvm/trunk/test/Analysis/ScalarEvolution/2008-02-11-ReversedCondition.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/ScalarEvolution/2008-02-11-ReversedCondition.ll?rev=46959&view=auto

==============================================================================
--- llvm/trunk/test/Analysis/ScalarEvolution/2008-02-11-ReversedCondition.ll (added)
+++ llvm/trunk/test/Analysis/ScalarEvolution/2008-02-11-ReversedCondition.ll Mon Feb 11 12:37:34 2008
@@ -0,0 +1,15 @@
+; RUN: llvm-as < %s | opt -scalar-evolution -analyze | not grep Unpredictable
+
+define void @foo(i32 %n) {
+entry:
+	br label %header
+header:
+	%i = phi i32 [ 0, %entry ], [ %i.inc, %next ]
+	%cond = icmp sgt i32 %n, %i
+	br i1 %cond, label %next, label %return
+next:
+        %i.inc = add i32 %i, 1
+	br label %header
+return:
+	ret void
+}