[LSR] Prevent formula with SCEVAddRecExpr type of Reg from Sibling loops

In rL294814, we allow formula with SCEVAddRecExpr type of Reg from loops
other than current loop. This is good for the case when induction variable
of outerloop being used in expr in innerloop. But it is very bad to allow
such Reg from sibling loop because we may need to add lsr.iv in other sibling
loops when scev expanding those SCEVAddRecExpr type exprs. For the testcase
below, one loop can be inserted with a bunch of lsr.iv because of LSR for
other loops.

// The induction variable j from a loop in the middle will have initial
// value generated from previous sibling loop and exit value used by its
// next sibling loop.
void goo(long i, long j);
long cond;

void foo(long N) {
long i = 0;
long j = 0;
i = 0; do { goo(i, j); i++; j++; } while (cond);
i = 0; do { goo(i, j); i++; j++; } while (cond);
i = 0; do { goo(i, j); i++; j++; } while (cond);
i = 0; do { goo(i, j); i++; j++; } while (cond);
i = 0; do { goo(i, j); i++; j++; } while (cond);
i = 0; do { goo(i, j); i++; j++; } while (cond);
}

The fix is to only allow formula with SCEVAddRecExpr type of Reg from current
loop or its parents.

Differential Revision: https://reviews.llvm.org/D30021

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@295378 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/lib/Transforms/Scalar/LoopStrengthReduce.cpp
index baef7b9a196f93494efb9eb702e0db8f27651be1..8cdfb3ad3f8bc5e3632fb3ff1e05af696051217e 100644 (file)
--- a/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ b/lib/Transforms/Scalar/LoopStrengthReduce.cpp
@@ -1119,6 +1119,13 @@ void Cost::RateRegister(const SCEV *Reg,
       if (isExistingPhi(AR, SE))
         return;
 
+      // It is bad to allow LSR for current loop to add induction variables
+      // for its sibling loops.
+      if (!AR->getLoop()->contains(L)) {
+        Lose();
+        return;
+      }
+
       // Otherwise, it will be an invariant with respect to Loop L.
       ++NumRegs;
       return;

diff --git a/test/Transforms/LoopStrengthReduce/X86/sibling-loops.ll b/test/Transforms/LoopStrengthReduce/X86/sibling-loops.ll
new file mode 100644 (file)
index 0000000..a69d6ad
--- /dev/null
+++ b/test/Transforms/LoopStrengthReduce/X86/sibling-loops.ll
@@ -0,0 +1,97 @@
+; RUN: opt -loop-reduce -S < %s | FileCheck %s
+; We find it is very bad to allow LSR formula containing SCEVAddRecExpr Reg
+; from siblings of current loop. When one loop is LSR optimized, it can
+; insert lsr.iv for other sibling loops, which sometimes leads to many extra
+; lsr.iv inserted for loops.
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+
+@cond = common local_unnamed_addr global i64 0, align 8
+
+; Check there is no extra lsr.iv generated in foo.
+; CHECK-LABEL: @foo(
+; CHECK-NOT: lsr.iv{{[0-9]+}} =
+;
+define void @foo(i64 %N) local_unnamed_addr {
+entry:
+  br label %do.body
+
+do.body:                                          ; preds = %do.body, %entry
+  %i.0 = phi i64 [ 0, %entry ], [ %inc, %do.body ]
+  tail call void @goo(i64 %i.0, i64 %i.0)
+  %inc = add nuw nsw i64 %i.0, 1
+  %t0 = load i64, i64* @cond, align 8
+  %tobool = icmp eq i64 %t0, 0
+  br i1 %tobool, label %do.body2.preheader, label %do.body
+
+do.body2.preheader:                               ; preds = %do.body
+  br label %do.body2
+
+do.body2:                                         ; preds = %do.body2.preheader, %do.body2
+  %i.1 = phi i64 [ %inc3, %do.body2 ], [ 0, %do.body2.preheader ]
+  %j.1 = phi i64 [ %inc4, %do.body2 ], [ %inc, %do.body2.preheader ]
+  tail call void @goo(i64 %i.1, i64 %j.1)
+  %inc3 = add nuw nsw i64 %i.1, 1
+  %inc4 = add nsw i64 %j.1, 1
+  %t1 = load i64, i64* @cond, align 8
+  %tobool6 = icmp eq i64 %t1, 0
+  br i1 %tobool6, label %do.body8.preheader, label %do.body2
+
+do.body8.preheader:                               ; preds = %do.body2
+  br label %do.body8
+
+do.body8:                                         ; preds = %do.body8.preheader, %do.body8
+  %i.2 = phi i64 [ %inc9, %do.body8 ], [ 0, %do.body8.preheader ]
+  %j.2 = phi i64 [ %inc10, %do.body8 ], [ %inc4, %do.body8.preheader ]
+  tail call void @goo(i64 %i.2, i64 %j.2)
+  %inc9 = add nuw nsw i64 %i.2, 1
+  %inc10 = add nsw i64 %j.2, 1
+  %t2 = load i64, i64* @cond, align 8
+  %tobool12 = icmp eq i64 %t2, 0
+  br i1 %tobool12, label %do.body14.preheader, label %do.body8
+
+do.body14.preheader:                              ; preds = %do.body8
+  br label %do.body14
+
+do.body14:                                        ; preds = %do.body14.preheader, %do.body14
+  %i.3 = phi i64 [ %inc15, %do.body14 ], [ 0, %do.body14.preheader ]
+  %j.3 = phi i64 [ %inc16, %do.body14 ], [ %inc10, %do.body14.preheader ]
+  tail call void @goo(i64 %i.3, i64 %j.3)
+  %inc15 = add nuw nsw i64 %i.3, 1
+  %inc16 = add nsw i64 %j.3, 1
+  %t3 = load i64, i64* @cond, align 8
+  %tobool18 = icmp eq i64 %t3, 0
+  br i1 %tobool18, label %do.body20.preheader, label %do.body14
+
+do.body20.preheader:                              ; preds = %do.body14
+  br label %do.body20
+
+do.body20:                                        ; preds = %do.body20.preheader, %do.body20
+  %i.4 = phi i64 [ %inc21, %do.body20 ], [ 0, %do.body20.preheader ]
+  %j.4 = phi i64 [ %inc22, %do.body20 ], [ %inc16, %do.body20.preheader ]
+  tail call void @goo(i64 %i.4, i64 %j.4)
+  %inc21 = add nuw nsw i64 %i.4, 1
+  %inc22 = add nsw i64 %j.4, 1
+  %t4 = load i64, i64* @cond, align 8
+  %tobool24 = icmp eq i64 %t4, 0
+  br i1 %tobool24, label %do.body26.preheader, label %do.body20
+
+do.body26.preheader:                              ; preds = %do.body20
+  br label %do.body26
+
+do.body26:                                        ; preds = %do.body26.preheader, %do.body26
+  %i.5 = phi i64 [ %inc27, %do.body26 ], [ 0, %do.body26.preheader ]
+  %j.5 = phi i64 [ %inc28, %do.body26 ], [ %inc22, %do.body26.preheader ]
+  tail call void @goo(i64 %i.5, i64 %j.5)
+  %inc27 = add nuw nsw i64 %i.5, 1
+  %inc28 = add nsw i64 %j.5, 1
+  %t5 = load i64, i64* @cond, align 8
+  %tobool30 = icmp eq i64 %t5, 0
+  br i1 %tobool30, label %do.end31, label %do.body26
+
+do.end31:                                         ; preds = %do.body26
+  ret void
+}
+
+declare void @goo(i64, i64) local_unnamed_addr
+