Fix a corner case hit by redundant phi elimination running after LSR.

Fixes PR11761: bad IR w/ redundant Phi elim


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@148177 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Analysis/ScalarEvolutionExpander.cpp

@@ -1541,6 +1541,13 @@ SCEVExpander::getOrInsertCanonicalInductionVariable(const Loop *L,
 /// general code-insertion helper.
 bool SCEVExpander::hoistStep(Instruction *IncV, Instruction *InsertPos,
                              const DominatorTree *DT) {
+  // Phi nodes are strangely positional but don't follow normal rules for
+  // instruction dominance. Handle them immediately.
+  if (isa<PHINode>(InsertPos))
+    return isa<PHINode>(IncV);
+  else if (isa<PHINode>(IncV))
+    return false;
+
   if (DT->dominates(IncV, InsertPos))
     return true;
 
@@ -1648,7 +1655,10 @@ unsigned SCEVExpander::replaceCongruentIVs(Loop *L, const DominatorTree *DT,
                         << *IsomorphicInc << '\n');
         Value *NewInc = OrigInc;
         if (OrigInc->getType() != IsomorphicInc->getType()) {
-          IRBuilder<> Builder(OrigInc->getNextNode());
+          Instruction *IP = isa<PHINode>(OrigInc)
+            ? (Instruction*)L->getHeader()->getFirstInsertionPt()
+            : OrigInc->getNextNode();
+          IRBuilder<> Builder(IP);
           Builder.SetCurrentDebugLocation(IsomorphicInc->getDebugLoc());
           NewInc = Builder.
             CreateTruncOrBitCast(OrigInc, IsomorphicInc->getType(), IVName);

test/Transforms/LoopStrengthReduce/X86/2012-01-13-phielim.ll

@@ -0,0 +1,50 @@
+; RUN: llc < %s -O3 -march=x86-64 -mcpu=core2 | FileCheck %s
+
+declare i1 @check() nounwind
+declare i1 @foo(i8*, i8*, i8*) nounwind
+
+; Check that redundant phi elimination ran
+; CHECK: @test
+; CHECK: %while.body.i
+; CHECK: movs
+; CHECK-NOT: movs
+; CHECK: %for.end.i
+define i32 @test(i8* %base) nounwind uwtable ssp {
+entry:
+  br label %while.body.lr.ph.i
+
+while.body.lr.ph.i:                               ; preds = %cond.true.i
+  br label %while.body.i
+
+while.body.i:                                     ; preds = %cond.true29.i, %while.body.lr.ph.i
+  %indvars.iv7.i = phi i64 [ 16, %while.body.lr.ph.i ], [ %indvars.iv.next8.i, %cond.true29.i ]
+  %i.05.i = phi i64 [ 0, %while.body.lr.ph.i ], [ %indvars.iv7.i, %cond.true29.i ]
+  %sext.i = shl i64 %i.05.i, 32
+  %idx.ext.i = ashr exact i64 %sext.i, 32
+  %add.ptr.sum.i = add i64 %idx.ext.i, 16
+  br label %for.body.i
+
+for.body.i:                                       ; preds = %for.body.i, %while.body.i
+  %indvars.iv.i = phi i64 [ 0, %while.body.i ], [ %indvars.iv.next.i, %for.body.i ]
+  %add.ptr.sum = add i64 %add.ptr.sum.i, %indvars.iv.i
+  %arrayidx22.i = getelementptr inbounds i8* %base, i64 %add.ptr.sum
+  %0 = load i8* %arrayidx22.i, align 1
+  %indvars.iv.next.i = add i64 %indvars.iv.i, 1
+  %cmp = call i1 @check() nounwind
+  br i1 %cmp, label %for.end.i, label %for.body.i
+
+for.end.i:                                        ; preds = %for.body.i
+  %add.ptr.i144 = getelementptr inbounds i8* %base, i64 %add.ptr.sum.i
+  %cmp2 = tail call i1 @foo(i8* %add.ptr.i144, i8* %add.ptr.i144, i8* undef) nounwind
+  br i1 %cmp2, label %cond.true29.i, label %cond.false35.i
+
+cond.true29.i:                                    ; preds = %for.end.i
+  %indvars.iv.next8.i = add i64 %indvars.iv7.i, 16
+  br i1 false, label %exit, label %while.body.i
+
+cond.false35.i:                                   ; preds = %for.end.i
+  unreachable
+
+exit:                                 ; preds = %cond.true29.i, %cond.true.i
+  ret i32 0
+}