From 361e54d433e67db5d6b6455f7fd098de8c01f882 Mon Sep 17 00:00:00 2001
From: Eli Friedman <eli.friedman@gmail.com>
Date: Sat, 9 May 2009 12:32:42 +0000
Subject: [PATCH] Allow scalar evolution to compute iteration counts for loops
 with a pointer-based condition.  This fixes PR3171.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@71354 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Analysis/ScalarEvolution.cpp              | 25 +++++------------
 .../2009-05-09-PointerEdgeCount.ll            | 27 +++++++++++++++++++
 2 files changed, 34 insertions(+), 18 deletions(-)
 create mode 100644 test/Analysis/ScalarEvolution/2009-05-09-PointerEdgeCount.ll

diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp
index e65cdd218a7..107a7c4d818 100644
--- a/lib/Analysis/ScalarEvolution.cpp
+++ b/lib/Analysis/ScalarEvolution.cpp
@@ -2372,10 +2372,8 @@ ScalarEvolution::ComputeBackedgeTakenCount(const Loop *L) {
   
   ICmpInst *ExitCond = dyn_cast<ICmpInst>(ExitBr->getCondition());
 
-  // If it's not an integer comparison then compute it the hard way. 
-  // Note that ICmpInst deals with pointer comparisons too so we must check
-  // the type of the operand.
-  if (ExitCond == 0 || isa<PointerType>(ExitCond->getOperand(0)->getType()))
+  // If it's not an integer or pointer comparison then compute it the hard way.
+  if (ExitCond == 0)
     return ComputeBackedgeTakenCountExhaustively(L, ExitBr->getCondition(),
                                           ExitBr->getSuccessor(0) == ExitBlock);
 
@@ -2416,21 +2414,12 @@ ScalarEvolution::ComputeBackedgeTakenCount(const Loop *L) {
   if (const SCEVConstant *RHSC = dyn_cast<SCEVConstant>(RHS))
     if (const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(LHS))
       if (AddRec->getLoop() == L) {
-        // Form the comparison range using the constant of the correct type so
-        // that the ConstantRange class knows to do a signed or unsigned
-        // comparison.
-        ConstantInt *CompVal = RHSC->getValue();
-        const Type *RealTy = ExitCond->getOperand(0)->getType();
-        CompVal = dyn_cast<ConstantInt>(
-          ConstantExpr::getBitCast(CompVal, RealTy));
-        if (CompVal) {
-          // Form the constant range.
-          ConstantRange CompRange(
-              ICmpInst::makeConstantRange(Cond, CompVal->getValue()));
+        // Form the constant range.
+        ConstantRange CompRange(
+            ICmpInst::makeConstantRange(Cond, RHSC->getValue()->getValue()));
 
-          SCEVHandle Ret = AddRec->getNumIterationsInRange(CompRange, *this);
-          if (!isa<SCEVCouldNotCompute>(Ret)) return Ret;
-        }
+        SCEVHandle Ret = AddRec->getNumIterationsInRange(CompRange, *this);
+        if (!isa<SCEVCouldNotCompute>(Ret)) return Ret;
       }
 
   switch (Cond) {
diff --git a/test/Analysis/ScalarEvolution/2009-05-09-PointerEdgeCount.ll b/test/Analysis/ScalarEvolution/2009-05-09-PointerEdgeCount.ll
new file mode 100644
index 00000000000..bea46a765d6
--- /dev/null
+++ b/test/Analysis/ScalarEvolution/2009-05-09-PointerEdgeCount.ll
@@ -0,0 +1,27 @@
+; RUN: llvm-as < %s | opt -analyze -scalar-evolution | grep {count is 2}
+; PR3171
+
+	%struct.Foo = type { i32 }
+	%struct.NonPod = type { [2 x %struct.Foo] }
+
+define void @_Z3foov() nounwind {
+entry:
+	%x = alloca %struct.NonPod, align 8		; <%struct.NonPod*> [#uses=2]
+	%0 = getelementptr %struct.NonPod* %x, i32 0, i32 0		; <[2 x %struct.Foo]*> [#uses=1]
+	%1 = getelementptr [2 x %struct.Foo]* %0, i32 1, i32 0		; <%struct.Foo*> [#uses=1]
+	br label %bb1.i
+
+bb1.i:		; preds = %bb2.i, %entry
+	%.0.i = phi %struct.Foo* [ %1, %entry ], [ %4, %bb2.i ]		; <%struct.Foo*> [#uses=2]
+	%2 = getelementptr %struct.NonPod* %x, i32 0, i32 0, i32 0		; <%struct.Foo*> [#uses=1]
+	%3 = icmp eq %struct.Foo* %.0.i, %2		; <i1> [#uses=1]
+	br i1 %3, label %_ZN6NonPodD1Ev.exit, label %bb2.i
+
+bb2.i:		; preds = %bb1.i
+	%4 = getelementptr %struct.Foo* %.0.i, i32 -1		; <%struct.Foo*> [#uses=1]
+	br label %bb1.i
+
+_ZN6NonPodD1Ev.exit:		; preds = %bb1.i
+	ret void
+}
+