Tweak IVUsers' concept of "interesting" to exclude add recurrences

where the step value is an induction variable from an outer loop, to
avoid trouble trying to re-expand such expressions. This effectively
hides such expressions from indvars and lsr, which prevents them
from getting into trouble.

llvm-svn: 111317

llvm/lib/Analysis/IVUsers.cpp

@@ -38,27 +38,31 @@ Pass *llvm::createIVUsersPass() {
 /// isInteresting - Test whether the given expression is "interesting" when
 /// used by the given expression, within the context of analyzing the
 /// given loop.
-static bool isInteresting(const SCEV *S, const Instruction *I, const Loop *L) {
-  // Anything loop-invariant is interesting.
-  if (!isa<SCEVUnknown>(S) && S->isLoopInvariant(L))
-    return true;
-
+static bool isInteresting(const SCEV *S, const Instruction *I, const Loop *L,
+                          ScalarEvolution *SE) {
   // An addrec is interesting if it's affine or if it has an interesting start.
   if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
     // Keep things simple. Don't touch loop-variant strides.
     if (AR->getLoop() == L)
       return AR->isAffine() || !L->contains(I);
-    // Otherwise recurse to see if the start value is interesting.
-    return isInteresting(AR->getStart(), I, L);
+    // Otherwise recurse to see if the start value is interesting, and that
+    // the step value is not interesting, since we don't yet know how to
+    // do effective SCEV expansions for addrecs with interesting steps.
+    return isInteresting(AR->getStart(), I, L, SE) &&
+          !isInteresting(AR->getStepRecurrence(*SE), I, L, SE);
   }
 
-  // An add is interesting if any of its operands is.
+  // An add is interesting if exactly one of its operands is interesting.
   if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
+    bool AnyInterestingYet = false;
     for (SCEVAddExpr::op_iterator OI = Add->op_begin(), OE = Add->op_end();
          OI != OE; ++OI)
-      if (isInteresting(*OI, I, L))
-        return true;
-    return false;
+      if (isInteresting(*OI, I, L, SE)) {
+        if (AnyInterestingYet)
+          return false;
+        AnyInterestingYet = true;
+      }
+    return AnyInterestingYet;
   }
 
   // Nothing else is interesting here.
@@ -84,7 +88,7 @@ bool IVUsers::AddUsersIfInteresting(Instruction *I) {
 
   // If we've come to an uninteresting expression, stop the traversal and
   // call this a user.
-  if (!isInteresting(ISE, I, L))
+  if (!isInteresting(ISE, I, L, SE))
     return false;
 
   SmallPtrSet<Instruction *, 4> UniqueUsers;

llvm/test/CodeGen/X86/licm-nested.ll

@@ -1,4 +1,4 @@
-; RUN: llc -mtriple=x86_64-apple-darwin -march=x86-64 < %s -stats -info-output-file - | grep machine-licm | grep 2
+; RUN: llc -mtriple=x86_64-apple-darwin -march=x86-64 < %s -stats -info-output-file - | grep machine-licm | grep 3
 
 ; MachineLICM should be able to hoist the symbolic addresses out of
 ; the inner loops.

llvm/test/CodeGen/X86/lsr-interesting-step.ll

@@ -0,0 +1,51 @@
+; RUN: llc < %s -march=x86-64 -relocation-model=static -mtriple=x86_64-unknown-linux-gnu
+
+; The inner loop should require only one add (and no leas either).
+; rdar://8100380
+
+; CHECK:      BB0_4:
+; CHECK-NEXT:   movb    $0, flags(%rdx)
+; CHECK-NEXT:   addq    %rcx, %rdx
+; CHECK-NEXT:   cmpq    $8192, %rdx
+; CHECK-NEXT:   jl
+
+@flags = external global [8192 x i8], align 16 ; <[8192 x i8]*> [#uses=1]
+
+define void @foo() nounwind {
+entry:
+  %tmp = icmp slt i64 2, 8192                     ; <i1> [#uses=1]
+  br i1 %tmp, label %bb, label %bb21
+
+bb:                                               ; preds = %entry
+  br label %bb7
+
+bb7:                                              ; preds = %bb, %bb17
+  %tmp8 = phi i64 [ %tmp18, %bb17 ], [ 2, %bb ]   ; <i64> [#uses=2]
+  %tmp9 = icmp slt i64 2, 8192                    ; <i1> [#uses=1]
+  br i1 %tmp9, label %bb10, label %bb17
+
+bb10:                                             ; preds = %bb7
+  br label %bb11
+
+bb11:                                             ; preds = %bb10, %bb11
+  %tmp12 = phi i64 [ %tmp14, %bb11 ], [ 2, %bb10 ] ; <i64> [#uses=2]
+  %tmp13 = getelementptr inbounds [8192 x i8]* @flags, i64 0, i64 %tmp12 ; <i8*> [#uses=1]
+  store i8 0, i8* %tmp13, align 1
+  %tmp14 = add nsw i64 %tmp12, %tmp8              ; <i64> [#uses=2]
+  %tmp15 = icmp slt i64 %tmp14, 8192              ; <i1> [#uses=1]
+  br i1 %tmp15, label %bb11, label %bb16
+
+bb16:                                             ; preds = %bb11
+  br label %bb17
+
+bb17:                                             ; preds = %bb16, %bb7
+  %tmp18 = add nsw i64 %tmp8, 1                   ; <i64> [#uses=2]
+  %tmp19 = icmp slt i64 %tmp18, 8192              ; <i1> [#uses=1]
+  br i1 %tmp19, label %bb7, label %bb20
+
+bb20:                                             ; preds = %bb17
+  br label %bb21
+
+bb21:                                             ; preds = %bb20, %entry
+  ret void
+}