[ScalarEvolution] Fix base condition in isNormalAddRecPHI.

Summary:
The function is meant to recurse until it comes upon the
phi it's looking for. However, with the current condition,
it will recurse until it finds anything _but_ the phi.

The function will even fail for simple cases like:
  %i = phi i32 [ %inc, %loop ], ...
  ...
  %inc = add i32 %i, 1

because the base condition will not happen when the phi
is recursed to, and the recursion will end with a 'false'
result since the previous instruction is a phi.

Reviewers: sanjoy, atrick

Reviewed By: sanjoy

Subscribers: Ka-Ka, bjope, llvm-commits

Committing on behalf of: Bevin Hansson (bevinh)

Differential Revision: https://reviews.llvm.org/D40946

llvm-svn: 320700

lib/Analysis/ScalarEvolutionExpander.cpp

@@ -878,7 +878,7 @@ bool SCEVExpander::isNormalAddRecExprPHI(PHINode *PN, Instruction *IncV,
   if (IncV->mayHaveSideEffects())
     return false;
 
-  if (IncV != PN)
+  if (IncV == PN)
     return true;
 
   return isNormalAddRecExprPHI(PN, IncV, L);

test/Transforms/IndVarSimplify/scevexpander-phi-base-case.ll

@@ -0,0 +1,63 @@
+; RUN: opt -indvars -S < %s | FileCheck %s
+
+define i32 @fn() {
+entry:
+  ret i32 10
+}
+
+define i32 @test_nested2(i32 %tnr) {
+; CHECK-LABEL: test_nested2
+; CHECK-NOT: %indvars.iv
+; CHECK: %i.0
+
+; indvars should not replace the i.0 variable with a new one; SCEVExpander
+; should determine that the old one is good to reuse.
+
+entry:
+  %res = alloca i32, align 4
+  store volatile i32 0, i32* %res, align 4
+  %call = call i32 @fn()
+  br label %for.cond
+
+for.cond:                                         ; preds = %for.inc6, %entry
+  %i.0 = phi i32 [ 0, %entry ], [ %inc7, %for.inc6 ]
+  %cmp = icmp slt i32 %i.0, %call
+  br i1 %cmp, label %for.body, label %for.cond.cleanup
+
+for.cond.cleanup:                                 ; preds = %for.cond
+  br label %for.end8
+
+for.body:                                         ; preds = %for.cond
+  br label %for.cond1
+
+for.cond1:                                        ; preds = %for.inc, %for.body
+  %j.0 = phi i32 [ 0, %for.body ], [ %inc5, %for.inc ]
+  %cmp2 = icmp slt i32 %j.0, %i.0
+  br i1 %cmp2, label %for.body4, label %for.cond.cleanup3
+
+for.cond.cleanup3:                                ; preds = %for.cond1
+  br label %for.end
+
+for.body4:                                        ; preds = %for.cond1
+  %0 = load volatile i32, i32* %res, align 4
+  %inc = add nsw i32 %0, 1
+  store volatile i32 %inc, i32* %res, align 4
+  br label %for.inc
+
+for.inc:                                          ; preds = %for.body4
+  %inc5 = add nsw i32 %j.0, 1
+  br label %for.cond1
+
+for.end:                                          ; preds = %for.cond.cleanup3
+  br label %for.inc6
+
+for.inc6:                                         ; preds = %for.end
+  %inc7 = add nsw i32 %i.0, 1
+  br label %for.cond
+
+for.end8:                                         ; preds = %for.cond.cleanup
+  %1 = load volatile i32, i32* %res, align 4
+  %cmp9 = icmp eq i32 %1, 45
+  %conv = zext i1 %cmp9 to i32
+  ret i32 %conv
+}