Sneaky, sneaky: move the -1 to the outside of the SMax. Reinstate the

optimization of SGE/SLE with unit stride, now that it works properly.

llvm-svn: 60881

1 files changed, 15 insertions, 15 deletions

diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 2b714de3b3f..1dd5026d749 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -2924,8 +2924,12 @@ bool ScalarEvolutionsImpl::potentialInfiniteLoop(SCEV *Stride, SCEV *RHS,
   if (!R)
     return true;
 
-  if (isSigned)
+  if (isSigned) {
+    if (SC->getValue()->isOne())
+      return R->getValue()->isMaxValue(true);
+
     return true;  // XXX: because we don't have an sdiv scev.
+  }
 
   // If negative, it wraps around every iteration, but we don't care about that.
   APInt S = SC->getValue()->getValue().abs();
@@ -2971,14 +2975,6 @@ HowManyLessThans(SCEV *LHS, SCEV *RHS, const Loop *L,
     // run (m-n)/s times.
     SCEVHandle End = RHS;
 
-    if (!executesAtLeastOnce(L, isSigned, trueWhenEqual,
-                             SE.getMinusSCEV(Start, One), RHS)) {
-      // If not, we get the value of the LHS in the first iteration in which
-      // the above condition doesn't hold.  This equals to max(m,n).
-      End = isSigned ? SE.getSMaxExpr(RHS, Start)
-                     : SE.getUMaxExpr(RHS, Start);
-    }
-
     // If the expression is less-than-or-equal to, we need to extend the
     // loop by one iteration.
     //
@@ -2987,12 +2983,16 @@ HowManyLessThans(SCEV *LHS, SCEV *RHS, const Loop *L,
     // division would equal one, but the loop runs twice putting the
     // induction variable at 12.
 
-    if (!trueWhenEqual)
-      // (Stride - 1) is correct only because we know it's unsigned.
-      // What we really want is to decrease the magnitude of Stride by one.
-      Start = SE.getMinusSCEV(Start, SE.getMinusSCEV(Stride, One));
-    else
-      Start = SE.getMinusSCEV(Start, Stride);
+    if (trueWhenEqual)
+      End = SE.getAddExpr(End, One);
+
+    if (!executesAtLeastOnce(L, isSigned, trueWhenEqual,
+                             SE.getMinusSCEV(Start, One), RHS)) {
+      // If not, we get the value of the LHS in the first iteration in which
+      // the above condition doesn't hold.  This equals to max(m,n).
+      End = isSigned ? SE.getSMaxExpr(End, Start)
+                     : SE.getUMaxExpr(End, Start);
+    }
 
     // Finally, we subtract these two values to get the number of times the
     // backedge is executed: max(m,n)-n.