[llvm-commits] [llvm] r60881 - in /llvm/trunk: lib/Analysis/ScalarEvolution.cpp test/Analysis/ScalarEvolution/2008-12-08-FiniteSGE.ll test/Analysis/ScalarEvolution/2008-12-11-SMaxOverflow.ll

[Nick Lewycky]

Author: nicholas
Date: Thu Dec 11 11:40:14 2008
New Revision: 60881

URL: http://llvm.org/viewvc/llvm-project?rev=60881&view=rev
Log:
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.

Added:
    llvm/trunk/test/Analysis/ScalarEvolution/2008-12-11-SMaxOverflow.ll
Modified:
    llvm/trunk/lib/Analysis/ScalarEvolution.cpp
    llvm/trunk/test/Analysis/ScalarEvolution/2008-12-08-FiniteSGE.ll

Modified: llvm/trunk/lib/Analysis/ScalarEvolution.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ScalarEvolution.cpp?rev=60881&r1=60880&r2=60881&view=diff

==============================================================================
--- llvm/trunk/lib/Analysis/ScalarEvolution.cpp (original)
+++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp Thu Dec 11 11:40:14 2008
@@ -2924,8 +2924,12 @@
   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 @@
     // 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 @@
     // 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.

Modified: llvm/trunk/test/Analysis/ScalarEvolution/2008-12-08-FiniteSGE.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/ScalarEvolution/2008-12-08-FiniteSGE.ll?rev=60881&r1=60880&r2=60881&view=diff

==============================================================================
--- llvm/trunk/test/Analysis/ScalarEvolution/2008-12-08-FiniteSGE.ll (original)
+++ llvm/trunk/test/Analysis/ScalarEvolution/2008-12-08-FiniteSGE.ll Thu Dec 11 11:40:14 2008
@@ -1,5 +1,4 @@
 ; RUN: llvm-as < %s | opt -analyze -scalar-evolution | grep {255 iterations}
-; XFAIL: *
 
 define i32 @foo(i32 %x, i32 %y, i32* %lam, i32* %alp) nounwind {
 bb1.thread:

Added: llvm/trunk/test/Analysis/ScalarEvolution/2008-12-11-SMaxOverflow.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/ScalarEvolution/2008-12-11-SMaxOverflow.ll?rev=60881&view=auto

==============================================================================
--- llvm/trunk/test/Analysis/ScalarEvolution/2008-12-11-SMaxOverflow.ll (added)
+++ llvm/trunk/test/Analysis/ScalarEvolution/2008-12-11-SMaxOverflow.ll Thu Dec 11 11:40:14 2008
@@ -0,0 +1,27 @@
+; RUN: llvm-as < %s | opt -analyze -scalar-evolution | grep {0 smax}
+
+define i32 @f(i32 %c.idx.val) {
+
+bb2:
+	%k.018 = add i32 %c.idx.val, -1		; <i32> [#uses=2]
+	%a14 = icmp slt i32 %k.018, 0		; <i1> [#uses=1]
+	br i1 %a14, label %bb19, label %bb16.preheader
+
+bb16.preheader:
+	%k.019 = phi i32 [ %k.0, %bb18 ], [ %k.018, %bb2 ]		; <i32> [#uses=5]
+	%x = phi i32 [ 0, %bb2 ], [ %x.1, %bb18]
+	br label %bb18
+
+bb18:		; preds = %bb18.loopexit
+	%x.1 = add i32 %x, 1
+	%k.0 = add i32 %k.019, -1		; <i32> [#uses=2]
+	%a107 = icmp slt i32 %k.0, 0		; <i1> [#uses=1]
+	br i1 %a107, label %bb18.bb19_crit_edge, label %bb16.preheader
+
+bb18.bb19_crit_edge:
+	ret i32 %x
+
+bb19:
+	ret i32 0
+
+}