[llvm] r276505 - [SCEV] Make isImpliedCondOperandsViaRanges smarter

[Sanjoy Das via llvm-commits]

Author: sanjoy
Date: Fri Jul 22 19:54:36 2016
New Revision: 276505

URL: http://llvm.org/viewvc/llvm-project?rev=276505&view=rev
Log:
[SCEV] Make isImpliedCondOperandsViaRanges smarter

This change lets us prove things like

  "{X,+,10} s< 5000" implies "{X+7,+,10} does not sign overflow"

It does this by replacing replacing getConstantDifference by
computeConstantDifference (which is smarter) in
isImpliedCondOperandsViaRanges.

Modified:
    llvm/trunk/include/llvm/Analysis/ScalarEvolution.h
    llvm/trunk/lib/Analysis/ScalarEvolution.cpp
    llvm/trunk/test/Analysis/ScalarEvolution/no-wrap-unknown-becount.ll

Modified: llvm/trunk/include/llvm/Analysis/ScalarEvolution.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Analysis/ScalarEvolution.h?rev=276505&r1=276504&r2=276505&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Analysis/ScalarEvolution.h (original)
+++ llvm/trunk/include/llvm/Analysis/ScalarEvolution.h Fri Jul 22 19:54:36 2016
@@ -1175,15 +1175,6 @@ namespace llvm {
     /// add recurrence on the loop \p L.
     bool isAddRecNeverPoison(const Instruction *I, const Loop *L);
 
-    /// Compute \p LHS - \p RHS and returns the result as an APInt if it is a
-    /// constant, and None if it isn't.
-    ///
-    /// This is intended to be a cheaper version of getMinusSCEV.  We can be
-    /// frugal here since we just bail out of actually constructing and
-    /// canonicalizing an expression in the cases where the result isn't going
-    /// to be a constant.
-    Optional<APInt> getConstantDifference(const SCEV *LHS, const SCEV *RHS);
-
   public:
     ScalarEvolution(Function &F, TargetLibraryInfo &TLI, AssumptionCache &AC,
                     DominatorTree &DT, LoopInfo &LI);

Modified: llvm/trunk/lib/Analysis/ScalarEvolution.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ScalarEvolution.cpp?rev=276505&r1=276504&r2=276505&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ScalarEvolution.cpp (original)
+++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp Fri Jul 22 19:54:36 2016
@@ -8571,16 +8571,6 @@ ScalarEvolution::isImpliedCondOperandsHe
   return false;
 }
 
-Optional<APInt> ScalarEvolution::getConstantDifference(const SCEV *LHS,
-                                                       const SCEV *RHS) {
-  if (const SCEVAddExpr *AddLHS = dyn_cast<SCEVAddExpr>(LHS))
-    if (AddLHS->getOperand(1) == RHS)
-      if (auto *Addend = dyn_cast<SCEVConstant>(AddLHS->getOperand(0)))
-        return Addend->getAPInt();
-
-  return None;
-}
-
 bool ScalarEvolution::isImpliedCondOperandsViaRanges(ICmpInst::Predicate Pred,
                                                      const SCEV *LHS,
                                                      const SCEV *RHS,
@@ -8591,7 +8581,7 @@ bool ScalarEvolution::isImpliedCondOpera
     // reduce the compile time impact of this optimization.
     return false;
 
-  Optional<APInt> Addend = getConstantDifference(LHS, FoundLHS);
+  Optional<APInt> Addend = computeConstantDifference(LHS, FoundLHS);
   if (!Addend)
     return false;
 

Modified: llvm/trunk/test/Analysis/ScalarEvolution/no-wrap-unknown-becount.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/ScalarEvolution/no-wrap-unknown-becount.ll?rev=276505&r1=276504&r2=276505&view=diff
==============================================================================
--- llvm/trunk/test/Analysis/ScalarEvolution/no-wrap-unknown-becount.ll (original)
+++ llvm/trunk/test/Analysis/ScalarEvolution/no-wrap-unknown-becount.ll Fri Jul 22 19:54:36 2016
@@ -63,6 +63,50 @@ leave:
   ret void
 }
 
+define void @s_3(i32 %start, i1* %cond) {
+; CHECK-LABEL: Classifying expressions for: @s_3
+entry:
+  br label %loop
+
+loop:
+  %iv = phi i32 [ %start, %entry ], [ %iv.inc, %be ]
+  %cmp = icmp slt i32 %iv, 10000
+  br i1 %cmp, label %be, label %leave
+
+be:
+  %iv.inc = add i32 %iv, 3
+  %iv.inc.sext = sext i32 %iv.inc to i64
+; CHECK:  %iv.inc.sext = sext i32 %iv.inc to i64
+; CHECK-NEXT:  -->  {(sext i32 (3 + %start) to i64),+,3}<nsw><%loop>
+  %c = load volatile i1, i1* %cond
+  br i1 %c, label %loop, label %leave
+
+leave:
+  ret void
+}
+
+define void @s_4(i32 %start, i1* %cond) {
+; CHECK-LABEL: Classifying expressions for: @s_4
+entry:
+  br label %loop
+
+loop:
+  %iv = phi i32 [ %start, %entry ], [ %iv.inc, %be ]
+  %cmp = icmp sgt i32 %iv, -1000
+  br i1 %cmp, label %be, label %leave
+
+be:
+  %iv.inc = add i32 %iv, -3
+  %iv.inc.sext = sext i32 %iv.inc to i64
+; CHECK:  %iv.inc.sext = sext i32 %iv.inc to i64
+; CHECK-NEXT:  -->  {(sext i32 (-3 + %start) to i64),+,-3}<nsw><%loop>
+  %c = load volatile i1, i1* %cond
+  br i1 %c, label %loop, label %leave
+
+leave:
+  ret void
+}
+
 define void @u_0(i32 %n, i1* %cond) {
 ; CHECK-LABEL: Classifying expressions for: @u_0
 entry:
@@ -119,6 +163,28 @@ loop:
   %c = load volatile i1, i1* %cond
   br i1 %c, label %loop, label %leave
 
+leave:
+  ret void
+}
+
+define void @u_3(i32 %start, i1* %cond) {
+; CHECK-LABEL: Classifying expressions for: @u_3
+entry:
+  br label %loop
+
+loop:
+  %iv = phi i32 [ %start, %entry ], [ %iv.inc, %be ]
+  %cmp = icmp ult i32 %iv, 10000
+  br i1 %cmp, label %be, label %leave
+
+be:
+  %iv.inc = add i32 %iv, 3
+  %iv.inc.zext = zext i32 %iv.inc to i64
+; CHECK:  %iv.inc.zext = zext i32 %iv.inc to i64
+; CHECK-NEXT:  -->  {(zext i32 (3 + %start) to i64),+,3}<nuw><%loop>
+  %c = load volatile i1, i1* %cond
+  br i1 %c, label %loop, label %leave
+
 leave:
   ret void
 }