Author: wmat
Date: Tue Feb 12 09:09:36 2008
New Revision: 47007
URL: http://llvm.org/viewvc/llvm-project?rev=47007view=rev
Log:
Fix PR2002. Suppose n is the initial value for the induction
variable (with step 1) and m is its final value. Then, the correct trip
count is SMAX(m,n)-n. Previously, we used SMAX(0,m-n), but m-n may
overflow and can't in general be interpreted as signed.
Patch by Nick Lewycky.
Added:
llvm/trunk/test/Analysis/ScalarEvolution/2008-02-12-SMAXTripCount.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=47007r1=47006r2=47007view=diff
==
--- llvm/trunk/lib/Analysis/ScalarEvolution.cpp (original)
+++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp Tue Feb 12 09:09:36 2008
@@ -2527,19 +2527,17 @@
if (AddRec-isAffine()) {
// The number of iterations for {n,+,1} m, is m-n. However, we don't
// know that m is = n on input to the loop. If it is, the condition
-// returns true zero times. To handle both cases, we return SMAX(0, m-n).
+// returns true zero times. To handle both cases, we return SMAX(m, n)-n.
// FORNOW: We only support unit strides.
SCEVHandle One = SE.getIntegerSCEV(1, RHS-getType());
if (AddRec-getOperand(1) != One)
return UnknownValue;
-SCEVHandle Iters = SE.getMinusSCEV(RHS, AddRec-getOperand(0));
+SCEVHandle Start = AddRec-getOperand(0);
+SCEVHandle End = isSigned ? SE.getSMaxExpr(RHS, Start) : (SCEVHandle)RHS;
-if (isSigned)
- return SE.getSMaxExpr(SE.getIntegerSCEV(0, RHS-getType()), Iters);
-else
- return Iters;
+return SE.getMinusSCEV(End, Start);
}
return UnknownValue;
Added: llvm/trunk/test/Analysis/ScalarEvolution/2008-02-12-SMAXTripCount.ll
URL:
http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/ScalarEvolution/2008-02-12-SMAXTripCount.ll?rev=47007view=auto
==
--- llvm/trunk/test/Analysis/ScalarEvolution/2008-02-12-SMAXTripCount.ll (added)
+++ llvm/trunk/test/Analysis/ScalarEvolution/2008-02-12-SMAXTripCount.ll Tue
Feb 12 09:09:36 2008
@@ -0,0 +1,16 @@
+; RUN: llvm-as %s | opt -scalar-evolution -analyze | grep {Loop loop: ( 100
+ ( -100 smax %n)) iterations!}
+; PR2002
+
+define void @foo(i8 %n) {
+entry:
+ br label %loop
+loop:
+ %i = phi i8 [ -100, %entry ], [ %i.inc, %next ]
+ %cond = icmp slt i8 %i, %n
+ br i1 %cond, label %next, label %return
+next:
+%i.inc = add i8 %i, 1
+ br label %loop
+return:
+ ret void
+}
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