[SCEV] Try to re-use pointer LCSSA phis when expanding SCEVs. #147824
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If an AddRec is expanded outside a loop with a single exit block, check if any of the (lcssa) phi nodes in the exit block match the AddRec. If that's the case, simply use the existing lcssa phi. This can reduce the number of instruction created for SCEV expansions, mainly for runtime checks generated by the loop vectorizer. Compile-time impact should be mostly neutral https://llvm-compile-time-tracker.com/compare.php?from=48c7a3187f9831304a38df9bdb3b4d5bf6b6b1a2&to=cf9d039a7b0db5d0d912e0e2c01b19c2a653273a&stat=instructions:u
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@llvm/pr-subscribers-llvm-transforms Author: Florian Hahn (fhahn) ChangesGeneralize the code added in A common source of integer AddRecs with pointer bases are runtime checks This improves codegen in some cases when vectorizing and prevents Full diff: https://github.com/llvm/llvm-project/pull/147824.diff 5 Files Affected:
diff --git a/llvm/include/llvm/Transforms/Utils/ScalarEvolutionExpander.h b/llvm/include/llvm/Transforms/Utils/ScalarEvolutionExpander.h
index a101151eed7cc..39fef921a9590 100644
--- a/llvm/include/llvm/Transforms/Utils/ScalarEvolutionExpander.h
+++ b/llvm/include/llvm/Transforms/Utils/ScalarEvolutionExpander.h
@@ -530,6 +530,7 @@ class SCEVExpander : public SCEVVisitor<SCEVExpander, Value *> {
bool isExpandedAddRecExprPHI(PHINode *PN, Instruction *IncV, const Loop *L);
+ Value *tryToReuseLCSSAPhi(const SCEVAddRecExpr *S);
Value *expandAddRecExprLiterally(const SCEVAddRecExpr *);
PHINode *getAddRecExprPHILiterally(const SCEVAddRecExpr *Normalized,
const Loop *L, Type *&TruncTy,
diff --git a/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp b/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
index 24fe08d6c3e4e..ca9183b91a19b 100644
--- a/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
+++ b/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
@@ -1223,6 +1223,39 @@ Value *SCEVExpander::expandAddRecExprLiterally(const SCEVAddRecExpr *S) {
return Result;
}
+Value *SCEVExpander::tryToReuseLCSSAPhi(const SCEVAddRecExpr *S) {
+ Type *STy = S->getType();
+ const Loop *L = S->getLoop();
+ BasicBlock *EB = L->getExitBlock();
+ if (!EB || !EB->getSinglePredecessor() ||
+ !SE.DT.dominates(EB, Builder.GetInsertBlock()))
+ return nullptr;
+
+ for (auto &PN : EB->phis()) {
+ if (!SE.isSCEVable(PN.getType()))
+ continue;
+ auto *ExitSCEV = SE.getSCEV(&PN);
+ Type *PhiTy = PN.getType();
+ if (STy->isIntegerTy() && PhiTy->isPointerTy())
+ ExitSCEV= SE.getPtrToIntExpr(ExitSCEV, STy);
+ else if (S->getType() != PN.getType())
+ continue;
+ const SCEV *Diff = SE.getMinusSCEV(S, ExitSCEV);
+ if (isa<SCEVCouldNotCompute>(Diff) ||
+ SCEVExprContains(Diff,
+ [](const SCEV *S) { return isa<SCEVAddRecExpr>(S); }))
+ continue;
+
+ Value *DiffV = expand(Diff);
+ Value *BaseV = &PN;
+ if (DiffV->getType()->isIntegerTy() && PhiTy->isPointerTy())
+ BaseV = Builder.CreatePtrToInt(BaseV, DiffV->getType());
+ return Builder.CreateAdd(BaseV, DiffV);
+ }
+
+ return nullptr;
+}
+
Value *SCEVExpander::visitAddRecExpr(const SCEVAddRecExpr *S) {
// In canonical mode we compute the addrec as an expression of a canonical IV
// using evaluateAtIteration and expand the resulting SCEV expression. This
@@ -1262,6 +1295,11 @@ Value *SCEVExpander::visitAddRecExpr(const SCEVAddRecExpr *S) {
return V;
}
+ // If there S is expanded outside the defining loop, check if there is a
+ // matching LCSSA phi node for it.
+ if (Value *V = tryToReuseLCSSAPhi(S))
+ return V;
+
// {X,+,F} --> X + {0,+,F}
if (!S->getStart()->isZero()) {
if (isa<PointerType>(S->getType())) {
diff --git a/llvm/test/Transforms/LoopLoadElim/invalidate-laa-after-versioning.ll b/llvm/test/Transforms/LoopLoadElim/invalidate-laa-after-versioning.ll
index 10e10653a431d..3ad262bb20910 100644
--- a/llvm/test/Transforms/LoopLoadElim/invalidate-laa-after-versioning.ll
+++ b/llvm/test/Transforms/LoopLoadElim/invalidate-laa-after-versioning.ll
@@ -59,19 +59,16 @@ define void @test(ptr %arg, i64 %arg1) {
; CHECK-NEXT: [[GEP_5:%.*]] = getelementptr inbounds double, ptr [[LCSSA_PTR_IV_1]], i64 1
; CHECK-NEXT: br label [[INNER_2:%.*]]
; CHECK: inner.2:
-; CHECK-NEXT: [[INDVAR:%.*]] = phi i64 [ [[INDVAR_NEXT:%.*]], [[INNER_2]] ], [ 0, [[INNER_1_EXIT]] ]
; CHECK-NEXT: [[PTR_IV_2:%.*]] = phi ptr [ [[GEP_5]], [[INNER_1_EXIT]] ], [ [[PTR_IV_2_NEXT:%.*]], [[INNER_2]] ]
; CHECK-NEXT: [[PTR_IV_2_NEXT]] = getelementptr inbounds double, ptr [[PTR_IV_2]], i64 1
-; CHECK-NEXT: [[INDVAR_NEXT]] = add i64 [[INDVAR]], 1
; CHECK-NEXT: br i1 false, label [[INNER_3_LVER_CHECK:%.*]], label [[INNER_2]]
; CHECK: inner.3.lver.check:
-; CHECK-NEXT: [[INDVAR_LCSSA:%.*]] = phi i64 [ [[INDVAR]], [[INNER_2]] ]
; CHECK-NEXT: [[LCSSA_PTR_IV_2:%.*]] = phi ptr [ [[PTR_IV_2]], [[INNER_2]] ]
; CHECK-NEXT: [[GEP_6:%.*]] = getelementptr inbounds double, ptr [[PTR_PHI]], i64 1
; CHECK-NEXT: [[GEP_7:%.*]] = getelementptr inbounds double, ptr [[LCSSA_PTR_IV_2]], i64 1
-; CHECK-NEXT: [[TMP0:%.*]] = shl i64 [[INDVAR_LCSSA]], 3
-; CHECK-NEXT: [[TMP1:%.*]] = add i64 [[TMP0]], 24
-; CHECK-NEXT: [[SCEVGEP3:%.*]] = getelementptr i8, ptr [[LCSSA_PTR_IV_1]], i64 [[TMP1]]
+; CHECK-NEXT: [[TMP0:%.*]] = ptrtoint ptr [[LCSSA_PTR_IV_2]] to i64
+; CHECK-NEXT: [[TMP1:%.*]] = add i64 [[TMP0]], 16
+; CHECK-NEXT: [[SCEVGEP3:%.*]] = inttoptr i64 [[TMP1]] to ptr
; CHECK-NEXT: [[BOUND0:%.*]] = icmp ult ptr [[GEP_7]], [[GEP_1]]
; CHECK-NEXT: [[BOUND1:%.*]] = icmp ult ptr [[PTR_PHI]], [[SCEVGEP3]]
; CHECK-NEXT: [[FOUND_CONFLICT:%.*]] = and i1 [[BOUND0]], [[BOUND1]]
@@ -104,7 +101,7 @@ define void @test(ptr %arg, i64 %arg1) {
; CHECK-NEXT: br i1 [[C_2]], label [[OUTER_LATCH_LOOPEXIT4:%.*]], label [[INNER_3]]
; CHECK: outer.latch.loopexit:
; CHECK-NEXT: br label [[OUTER_LATCH]]
-; CHECK: outer.latch.loopexit4:
+; CHECK: outer.latch.loopexit3:
; CHECK-NEXT: br label [[OUTER_LATCH]]
; CHECK: outer.latch:
; CHECK-NEXT: br label [[INNER_1_LVER_CHECK]]
diff --git a/llvm/test/Transforms/LoopVectorize/reuse-lcssa-phi-scev-expansion.ll b/llvm/test/Transforms/LoopVectorize/reuse-lcssa-phi-scev-expansion.ll
index 2747895f06a7b..cd2e5dd8055f2 100644
--- a/llvm/test/Transforms/LoopVectorize/reuse-lcssa-phi-scev-expansion.ll
+++ b/llvm/test/Transforms/LoopVectorize/reuse-lcssa-phi-scev-expansion.ll
@@ -18,11 +18,9 @@ define void @reuse_lcssa_phi_for_add_rec1(ptr %head) {
; CHECK-NEXT: [[IV_NEXT]] = add nuw i64 [[IV]], 1
; CHECK-NEXT: br i1 [[EC_1]], label %[[PH:.*]], label %[[LOOP_1]]
; CHECK: [[PH]]:
-; CHECK-NEXT: [[IV_2_LCSSA:%.*]] = phi i32 [ [[IV_2]], %[[LOOP_1]] ]
; CHECK-NEXT: [[IV_LCSSA:%.*]] = phi i64 [ [[IV]], %[[LOOP_1]] ]
-; CHECK-NEXT: [[IV_2_NEXT_LCSSA:%.*]] = phi i32 [ [[IV_2_NEXT]], %[[LOOP_1]] ]
+; CHECK-NEXT: [[TMP0:%.*]] = phi i32 [ [[IV_2_NEXT]], %[[LOOP_1]] ]
; CHECK-NEXT: [[SRC_2:%.*]] = tail call noalias noundef dereferenceable_or_null(8) ptr @calloc(i64 1, i64 8)
-; CHECK-NEXT: [[TMP0:%.*]] = add i32 [[IV_2_LCSSA]], 1
; CHECK-NEXT: [[SMIN:%.*]] = call i32 @llvm.smin.i32(i32 [[TMP0]], i32 1)
; CHECK-NEXT: [[TMP1:%.*]] = sub i32 [[TMP0]], [[SMIN]]
; CHECK-NEXT: [[TMP2:%.*]] = zext i32 [[TMP1]] to i64
@@ -106,27 +104,23 @@ define void @runtime_checks_ptr_inductions(ptr %dst.1, ptr %dst.2, i1 %c) {
; CHECK-LABEL: define void @runtime_checks_ptr_inductions(
; CHECK-SAME: ptr [[DST_1:%.*]], ptr [[DST_2:%.*]], i1 [[C:%.*]]) {
; CHECK-NEXT: [[ENTRY:.*]]:
-; CHECK-NEXT: [[DST_11:%.*]] = ptrtoint ptr [[DST_1]] to i64
; CHECK-NEXT: br label %[[LOOP_1:.*]]
; CHECK: [[LOOP_1]]:
-; CHECK-NEXT: [[INDVAR:%.*]] = phi i64 [ [[INDVAR_NEXT:%.*]], %[[LOOP_1]] ], [ 0, %[[ENTRY]] ]
; CHECK-NEXT: [[PTR_IV_1:%.*]] = phi ptr [ [[DST_1]], %[[ENTRY]] ], [ [[PTR_IV_1_NEXT:%.*]], %[[LOOP_1]] ]
; CHECK-NEXT: [[CALL:%.*]] = call i32 @val()
; CHECK-NEXT: [[SEL_DST:%.*]] = select i1 [[C]], ptr [[DST_1]], ptr [[DST_2]]
; CHECK-NEXT: [[PTR_IV_1_NEXT]] = getelementptr i8, ptr [[PTR_IV_1]], i64 1
; CHECK-NEXT: [[EC_1:%.*]] = icmp eq i32 [[CALL]], 0
-; CHECK-NEXT: [[INDVAR_NEXT]] = add i64 [[INDVAR]], 1
; CHECK-NEXT: br i1 [[EC_1]], label %[[LOOP_2_HEADER_PREHEADER:.*]], label %[[LOOP_1]]
; CHECK: [[LOOP_2_HEADER_PREHEADER]]:
-; CHECK-NEXT: [[SEL_DST_LCSSA2:%.*]] = phi ptr [ [[SEL_DST]], %[[LOOP_1]] ]
-; CHECK-NEXT: [[INDVAR_LCSSA:%.*]] = phi i64 [ [[INDVAR]], %[[LOOP_1]] ]
+; CHECK-NEXT: [[SEL_DST_LCSSA1:%.*]] = phi ptr [ [[SEL_DST]], %[[LOOP_1]] ]
; CHECK-NEXT: [[PTR_IV_1_LCSSA:%.*]] = phi ptr [ [[PTR_IV_1]], %[[LOOP_1]] ]
; CHECK-NEXT: [[SEL_DST_LCSSA:%.*]] = phi ptr [ [[SEL_DST]], %[[LOOP_1]] ]
-; CHECK-NEXT: [[SEL_DST_LCSSA23:%.*]] = ptrtoint ptr [[SEL_DST_LCSSA2]] to i64
+; CHECK-NEXT: [[SEL_DST_LCSSA12:%.*]] = ptrtoint ptr [[SEL_DST_LCSSA1]] to i64
; CHECK-NEXT: br i1 false, label %[[SCALAR_PH:.*]], label %[[VECTOR_MEMCHECK:.*]]
; CHECK: [[VECTOR_MEMCHECK]]:
-; CHECK-NEXT: [[TMP0:%.*]] = add i64 [[INDVAR_LCSSA]], [[DST_11]]
-; CHECK-NEXT: [[TMP1:%.*]] = sub i64 [[TMP0]], [[SEL_DST_LCSSA23]]
+; CHECK-NEXT: [[TMP0:%.*]] = ptrtoint ptr [[PTR_IV_1_LCSSA]] to i64
+; CHECK-NEXT: [[TMP1:%.*]] = sub i64 [[TMP0]], [[SEL_DST_LCSSA12]]
; CHECK-NEXT: [[DIFF_CHECK:%.*]] = icmp ult i64 [[TMP1]], 2
; CHECK-NEXT: br i1 [[DIFF_CHECK]], label %[[SCALAR_PH]], label %[[VECTOR_PH:.*]]
; CHECK: [[VECTOR_PH]]:
@@ -148,13 +142,13 @@ define void @runtime_checks_ptr_inductions(ptr %dst.1, ptr %dst.2, i1 %c) {
; CHECK-NEXT: br label %[[SCALAR_PH]]
; CHECK: [[SCALAR_PH]]:
; CHECK-NEXT: [[BC_RESUME_VAL:%.*]] = phi i32 [ 1023, %[[MIDDLE_BLOCK]] ], [ 1, %[[LOOP_2_HEADER_PREHEADER]] ], [ 1, %[[VECTOR_MEMCHECK]] ]
-; CHECK-NEXT: [[BC_RESUME_VAL5:%.*]] = phi ptr [ [[TMP2]], %[[MIDDLE_BLOCK]] ], [ [[PTR_IV_1_LCSSA]], %[[LOOP_2_HEADER_PREHEADER]] ], [ [[PTR_IV_1_LCSSA]], %[[VECTOR_MEMCHECK]] ]
-; CHECK-NEXT: [[BC_RESUME_VAL6:%.*]] = phi ptr [ [[TMP3]], %[[MIDDLE_BLOCK]] ], [ [[SEL_DST_LCSSA]], %[[LOOP_2_HEADER_PREHEADER]] ], [ [[SEL_DST_LCSSA]], %[[VECTOR_MEMCHECK]] ]
+; CHECK-NEXT: [[BC_RESUME_VAL4:%.*]] = phi ptr [ [[TMP2]], %[[MIDDLE_BLOCK]] ], [ [[PTR_IV_1_LCSSA]], %[[LOOP_2_HEADER_PREHEADER]] ], [ [[PTR_IV_1_LCSSA]], %[[VECTOR_MEMCHECK]] ]
+; CHECK-NEXT: [[BC_RESUME_VAL5:%.*]] = phi ptr [ [[TMP3]], %[[MIDDLE_BLOCK]] ], [ [[SEL_DST_LCSSA]], %[[LOOP_2_HEADER_PREHEADER]] ], [ [[SEL_DST_LCSSA]], %[[VECTOR_MEMCHECK]] ]
; CHECK-NEXT: br label %[[LOOP_2_HEADER:.*]]
; CHECK: [[LOOP_2_HEADER]]:
; CHECK-NEXT: [[IV:%.*]] = phi i32 [ [[DEC7:%.*]], %[[LOOP_2_LATCH:.*]] ], [ [[BC_RESUME_VAL]], %[[SCALAR_PH]] ]
-; CHECK-NEXT: [[PTR_IV_2:%.*]] = phi ptr [ [[PTR_IV_2_NEXT:%.*]], %[[LOOP_2_LATCH]] ], [ [[BC_RESUME_VAL5]], %[[SCALAR_PH]] ]
-; CHECK-NEXT: [[PTR_IV_3:%.*]] = phi ptr [ [[PTR_IV_3_NEXT:%.*]], %[[LOOP_2_LATCH]] ], [ [[BC_RESUME_VAL6]], %[[SCALAR_PH]] ]
+; CHECK-NEXT: [[PTR_IV_2:%.*]] = phi ptr [ [[PTR_IV_2_NEXT:%.*]], %[[LOOP_2_LATCH]] ], [ [[BC_RESUME_VAL4]], %[[SCALAR_PH]] ]
+; CHECK-NEXT: [[PTR_IV_3:%.*]] = phi ptr [ [[PTR_IV_3_NEXT:%.*]], %[[LOOP_2_LATCH]] ], [ [[BC_RESUME_VAL5]], %[[SCALAR_PH]] ]
; CHECK-NEXT: [[EC_2:%.*]] = icmp eq i32 [[IV]], 1024
; CHECK-NEXT: br i1 [[EC_2]], label %[[EXIT:.*]], label %[[LOOP_2_LATCH]]
; CHECK: [[LOOP_2_LATCH]]:
diff --git a/llvm/test/Transforms/LoopVersioning/invalidate-laa-after-versioning.ll b/llvm/test/Transforms/LoopVersioning/invalidate-laa-after-versioning.ll
index 8075314a65b49..858864276c0a0 100644
--- a/llvm/test/Transforms/LoopVersioning/invalidate-laa-after-versioning.ll
+++ b/llvm/test/Transforms/LoopVersioning/invalidate-laa-after-versioning.ll
@@ -56,19 +56,16 @@ define void @test(ptr %arg, i64 %arg1) {
; CHECK-NEXT: [[GEP_5:%.*]] = getelementptr inbounds double, ptr [[LCSSA_PTR_IV_1]], i64 1
; CHECK-NEXT: br label [[INNER_2:%.*]]
; CHECK: inner.2:
-; CHECK-NEXT: [[INDVAR:%.*]] = phi i64 [ [[INDVAR_NEXT:%.*]], [[INNER_2]] ], [ 0, [[INNER_1_EXIT]] ]
; CHECK-NEXT: [[PTR_IV_2:%.*]] = phi ptr [ [[GEP_5]], [[INNER_1_EXIT]] ], [ [[PTR_IV_2_NEXT:%.*]], [[INNER_2]] ]
; CHECK-NEXT: [[PTR_IV_2_NEXT]] = getelementptr inbounds double, ptr [[PTR_IV_2]], i64 1
-; CHECK-NEXT: [[INDVAR_NEXT]] = add i64 [[INDVAR]], 1
; CHECK-NEXT: br i1 false, label [[INNER_3_LVER_CHECK:%.*]], label [[INNER_2]]
; CHECK: inner.3.lver.check:
-; CHECK-NEXT: [[INDVAR_LCSSA:%.*]] = phi i64 [ [[INDVAR]], [[INNER_2]] ]
; CHECK-NEXT: [[LCSSA_PTR_IV_2:%.*]] = phi ptr [ [[PTR_IV_2]], [[INNER_2]] ]
; CHECK-NEXT: [[GEP_6:%.*]] = getelementptr inbounds double, ptr [[PTR_PHI]], i64 1
; CHECK-NEXT: [[GEP_7:%.*]] = getelementptr inbounds double, ptr [[LCSSA_PTR_IV_2]], i64 1
-; CHECK-NEXT: [[TMP0:%.*]] = shl i64 [[INDVAR_LCSSA]], 3
-; CHECK-NEXT: [[TMP1:%.*]] = add i64 [[TMP0]], 24
-; CHECK-NEXT: [[SCEVGEP:%.*]] = getelementptr i8, ptr [[LCSSA_PTR_IV_1]], i64 [[TMP1]]
+; CHECK-NEXT: [[TMP0:%.*]] = ptrtoint ptr [[LCSSA_PTR_IV_2]] to i64
+; CHECK-NEXT: [[TMP1:%.*]] = add i64 [[TMP0]], 16
+; CHECK-NEXT: [[SCEVGEP:%.*]] = inttoptr i64 [[TMP1]] to ptr
; CHECK-NEXT: [[BOUND0:%.*]] = icmp ult ptr [[GEP_7]], [[GEP_1]]
; CHECK-NEXT: [[BOUND1:%.*]] = icmp ult ptr [[PTR_PHI]], [[SCEVGEP]]
; CHECK-NEXT: [[FOUND_CONFLICT:%.*]] = and i1 [[BOUND0]], [[BOUND1]]
@@ -90,10 +87,10 @@ define void @test(ptr %arg, i64 %arg1) {
; CHECK: inner.3:
; CHECK-NEXT: [[IV_2:%.*]] = phi i64 [ 0, [[INNER_3_PH]] ], [ [[IV_2_NEXT:%.*]], [[INNER_3]] ]
; CHECK-NEXT: [[GEP_8:%.*]] = getelementptr inbounds double, ptr [[GEP_6]], i64 [[IV_2]]
-; CHECK-NEXT: store double 0.000000e+00, ptr [[GEP_7]], align 8, !alias.scope !0, !noalias !3
-; CHECK-NEXT: store double 0.000000e+00, ptr [[GEP_8]], align 8, !alias.scope !3
+; CHECK-NEXT: store double 0.000000e+00, ptr [[GEP_7]], align 8, !alias.scope [[META0:![0-9]+]], !noalias [[META3:![0-9]+]]
+; CHECK-NEXT: store double 0.000000e+00, ptr [[GEP_8]], align 8, !alias.scope [[META3]]
; CHECK-NEXT: [[GEP_9:%.*]] = getelementptr double, ptr [[PTR_PHI]], i64 [[IV_2]]
-; CHECK-NEXT: [[TMP18:%.*]] = load double, ptr [[GEP_9]], align 8, !alias.scope !3
+; CHECK-NEXT: [[TMP18:%.*]] = load double, ptr [[GEP_9]], align 8, !alias.scope [[META3]]
; CHECK-NEXT: [[IV_2_NEXT]] = add nuw nsw i64 [[IV_2]], 1
; CHECK-NEXT: [[C_2:%.*]] = icmp eq i64 [[IV_2]], 1
; CHECK-NEXT: br i1 [[C_2]], label [[OUTER_LATCH_LOOPEXIT3:%.*]], label [[INNER_3]]
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✅ With the latest revision this PR passed the C/C++ code formatter. |
Generalize the code added in llvm#147214 to also support re-using pointer LCSSA phis when expanding integer SCEVs with AddRecs. A common source of integer AddRecs with pointer bases are runtime checks emitted by LV based on the distance between 2 pointer AddRecs. This improves codegen in some cases when vectorizing and prevents regressions with llvm#142309, which turns some phis into single-entry ones, which SCEV will look through now (and expand the whole AddRec), whereas before it would have to treat the LCSSA phi as SCEVUnknown.
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Generalize the code added in
#147214 to also support
re-using pointer LCSSA phis when expanding integer SCEVs with AddRecs.
A common source of integer AddRecs with pointer bases are runtime checks
emitted by LV based on the distance between 2 pointer AddRecs.
This improves codegen in some cases when vectorizing and prevents
regressions with #142309, which
turns some phis into single-entry ones, which SCEV will look through
now (and expand the whole AddRec), whereas before it would have to treat
the LCSSA phi as SCEVUnknown.