[LoopNest] Consider loop nest with inner loop guard using outer loop

induction variable to be perfect

This patch allow more conditional branches to be considered as loop
guard, and so more loop nests can be considered perfect.

Reviewed By: bmahjour, sidbav

Differential Revision: https://reviews.llvm.org/D94717

diff --git a/llvm/include/llvm/Analysis/LoopNestAnalysis.h b/llvm/include/llvm/Analysis/LoopNestAnalysis.h
index ace1754..e045419 100644 (file)
--- a/llvm/include/llvm/Analysis/LoopNestAnalysis.h
+++ b/llvm/include/llvm/Analysis/LoopNestAnalysis.h
@@ -61,10 +61,12 @@ public:
   static unsigned getMaxPerfectDepth(const Loop &Root, ScalarEvolution &SE);
 
   /// Recursivelly traverse all empty 'single successor' basic blocks of \p From
-  /// (if there are any). Return the last basic block found or \p End if it was
-  /// reached during the search.
+  /// (if there are any). When \p CheckUniquePred is set to true, check if
+  /// each of the empty single successors has a unique predecessor. Return
+  /// the last basic block found or \p End if it was reached during the search.
   static const BasicBlock &skipEmptyBlockUntil(const BasicBlock *From,
-                                               const BasicBlock *End);
+                                               const BasicBlock *End,
+                                               bool CheckUniquePred = false);
 
   /// Return the outermost loop in the loop nest.
   Loop &getOutermostLoop() const { return *Loops.front(); }

diff --git a/llvm/lib/Analysis/LoopInfo.cpp b/llvm/lib/Analysis/LoopInfo.cpp
index adb2bdb..b2d7edb 100644 (file)
--- a/llvm/lib/Analysis/LoopInfo.cpp
+++ b/llvm/lib/Analysis/LoopInfo.cpp
@@ -20,6 +20,7 @@
 #include "llvm/Analysis/IVDescriptors.h"
 #include "llvm/Analysis/LoopInfoImpl.h"
 #include "llvm/Analysis/LoopIterator.h"
+#include "llvm/Analysis/LoopNestAnalysis.h"
 #include "llvm/Analysis/MemorySSA.h"
 #include "llvm/Analysis/MemorySSAUpdater.h"
 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
@@ -380,10 +381,6 @@ BranchInst *Loop::getLoopGuardBranch() const {
   if (!ExitFromLatch)
     return nullptr;
 
-  BasicBlock *ExitFromLatchSucc = ExitFromLatch->getUniqueSuccessor();
-  if (!ExitFromLatchSucc)
-    return nullptr;
-
   BasicBlock *GuardBB = Preheader->getUniquePredecessor();
   if (!GuardBB)
     return nullptr;
@@ -397,7 +394,17 @@ BranchInst *Loop::getLoopGuardBranch() const {
   BasicBlock *GuardOtherSucc = (GuardBI->getSuccessor(0) == Preheader)
                                    ? GuardBI->getSuccessor(1)
                                    : GuardBI->getSuccessor(0);
-  return (GuardOtherSucc == ExitFromLatchSucc) ? GuardBI : nullptr;
+
+  // Check if ExitFromLatch (or any BasicBlock which is an empty unique
+  // successor of ExitFromLatch) is equal to GuardOtherSucc. If
+  // skipEmptyBlockUntil returns GuardOtherSucc, then the guard branch for the
+  // loop is GuardBI (return GuardBI), otherwise return nullptr.
+  if (&LoopNest::skipEmptyBlockUntil(ExitFromLatch, GuardOtherSucc,
+                                     /*CheckUniquePred=*/true) ==
+      GuardOtherSucc)
+    return GuardBI;
+  else
+    return nullptr;
 }
 
 bool Loop::isCanonical(ScalarEvolution &SE) const {

diff --git a/llvm/lib/Analysis/LoopNestAnalysis.cpp b/llvm/lib/Analysis/LoopNestAnalysis.cpp
index ee74d4b..2649ed6 100644 (file)
--- a/llvm/lib/Analysis/LoopNestAnalysis.cpp
+++ b/llvm/lib/Analysis/LoopNestAnalysis.cpp
@@ -206,7 +206,8 @@ unsigned LoopNest::getMaxPerfectDepth(const Loop &Root, ScalarEvolution &SE) {
 }
 
 const BasicBlock &LoopNest::skipEmptyBlockUntil(const BasicBlock *From,
-                                                const BasicBlock *End) {
+                                                const BasicBlock *End,
+                                                bool CheckUniquePred) {
   assert(From && "Expecting valid From");
   assert(End && "Expecting valid End");
 
@@ -220,8 +221,9 @@ const BasicBlock &LoopNest::skipEmptyBlockUntil(const BasicBlock *From,
   // Visited is used to avoid running into an infinite loop.
   SmallPtrSet<const BasicBlock *, 4> Visited;
   const BasicBlock *BB = From->getUniqueSuccessor();
-  const BasicBlock *PredBB = BB;
-  while (BB && BB != End && IsEmpty(BB) && !Visited.count(BB)) {
+  const BasicBlock *PredBB = From;
+  while (BB && BB != End && IsEmpty(BB) && !Visited.count(BB) &&
+         (!CheckUniquePred || BB->getUniquePredecessor())) {
     Visited.insert(BB);
     PredBB = BB;
     BB = BB->getUniqueSuccessor();
@@ -335,9 +337,11 @@ static bool checkLoopsStructure(const Loop &OuterLoop, const Loop &InnerLoop,
 
   // Ensure the inner loop exit block lead to the outer loop latch possibly
   // through empty blocks.
-  const BasicBlock &SuccInner =
-      LoopNest::skipEmptyBlockUntil(InnerLoop.getExitBlock(), OuterLoopLatch);
-  if (&SuccInner != OuterLoopLatch && &SuccInner != ExtraPhiBlock) {
+  if ((!ExtraPhiBlock ||
+       &LoopNest::skipEmptyBlockUntil(InnerLoop.getExitBlock(),
+                                      ExtraPhiBlock) != ExtraPhiBlock) &&
+      (&LoopNest::skipEmptyBlockUntil(InnerLoop.getExitBlock(),
+                                      OuterLoopLatch) != OuterLoopLatch)) {
     DEBUG_WITH_TYPE(
         VerboseDebug,
         dbgs() << "Inner loop exit block " << *InnerLoopExit

diff --git a/llvm/test/Analysis/LoopNestAnalysis/imperfectnest.ll b/llvm/test/Analysis/LoopNestAnalysis/imperfectnest.ll
index 4c8066e..77b361b 100644 (file)
--- a/llvm/test/Analysis/LoopNestAnalysis/imperfectnest.ll
+++ b/llvm/test/Analysis/LoopNestAnalysis/imperfectnest.ll
@@ -424,70 +424,3 @@ for.cond.for.end13_crit_edge:
 for.end13:                   
   ret void
 }
-
-; Test an imperfect loop nest of the form:
-;   for (int i = 0; i < nx; ++i)
-;     if (i > 5) { // user branch
-;       for (int j = 1; j <= 5; j+=2)
-;         y[j][i] = x[i][j] + j;
-;     }
-
-define void @imperf_nest_6(i32** %y, i32** %x, i32 signext %nx, i32 signext %ny) {
-;    CHECK-LABEL: IsPerfect=false, Depth=2, OutermostLoop: imperf_nest_6_loop_i, Loops: ( imperf_nest_6_loop_i imperf_nest_6_loop_j )
-entry:
-  %cmp2 = icmp slt i32 0, %nx
-  br i1 %cmp2, label %imperf_nest_6_loop_i.lr.ph, label %for.end13
-
-imperf_nest_6_loop_i.lr.ph:
-  br label %imperf_nest_6_loop_i
-
-imperf_nest_6_loop_i:      
-  %i.0 = phi i32 [ 0, %imperf_nest_6_loop_i.lr.ph ], [ %inc12, %for.inc11 ]
-  %cmp1 = icmp sgt i32 %i.0, 5
-  br i1 %cmp1, label %imperf_nest_6_loop_j.lr.ph, label %if.end
-
-imperf_nest_6_loop_j.lr.ph:
-  br label %imperf_nest_6_loop_j
-
-imperf_nest_6_loop_j:      
-  %j.0 = phi i32 [ 1, %imperf_nest_6_loop_j.lr.ph ], [ %inc, %for.inc ]
-  %idxprom = sext i32 %i.0 to i64
-  %arrayidx = getelementptr inbounds i32*, i32** %x, i64 %idxprom
-  %0 = load i32*, i32** %arrayidx, align 8
-  %idxprom5 = sext i32 %j.0 to i64
-  %arrayidx6 = getelementptr inbounds i32, i32* %0, i64 %idxprom5
-  %1 = load i32, i32* %arrayidx6, align 4
-  %add = add nsw i32 %1, %j.0
-  %idxprom7 = sext i32 %j.0 to i64
-  %arrayidx8 = getelementptr inbounds i32*, i32** %y, i64 %idxprom7
-  %2 = load i32*, i32** %arrayidx8, align 8
-  %idxprom9 = sext i32 %i.0 to i64
-  %arrayidx10 = getelementptr inbounds i32, i32* %2, i64 %idxprom9
-  store i32 %add, i32* %arrayidx10, align 4
-  br label %for.inc
-
-for.inc:
-  %inc = add nsw i32 %j.0, 2
-  %cmp3 = icmp sle i32 %inc, 5
-  br i1 %cmp3, label %imperf_nest_6_loop_j, label %for.cond2.for.end_crit_edge
-
-for.cond2.for.end_crit_edge:
-  br label %for.end
-
-for.end:                    
-  br label %if.end
-
-if.end:                     
-  br label %for.inc11
-
-for.inc11:                  
-  %inc12 = add nsw i32 %i.0, 1
-  %cmp = icmp slt i32 %inc12, %nx
-  br i1 %cmp, label %imperf_nest_6_loop_i, label %for.cond.for.end13_crit_edge
-
-for.cond.for.end13_crit_edge:
-  br label %for.end13
-
-for.end13:                   
-  ret void
-}

diff --git a/llvm/test/Analysis/LoopNestAnalysis/perfectnest.ll b/llvm/test/Analysis/LoopNestAnalysis/perfectnest.ll
index 7593d6f..f8b0e6a 100644 (file)
--- a/llvm/test/Analysis/LoopNestAnalysis/perfectnest.ll
+++ b/llvm/test/Analysis/LoopNestAnalysis/perfectnest.ll
@@ -322,3 +322,148 @@ for.end7:
   %x.addr.0.lcssa = phi i32 [ %split7, %for.cond.for.end7_crit_edge ], [ %x, %entry ]
   ret i32 %x.addr.0.lcssa
 }
+
+; Test a perfect loop nest of the form:
+;   for (int i = 0; i < nx; ++i)
+;     if (i < ny) { // guard branch for the j-loop
+;       for (int j=i; j < ny; j+=1)
+;         y[j][i] = x[i][j] + j;
+;     }
+define double @perf_nest_guard_branch(i32** %y, i32** %x, i32 signext %nx, i32 signext %ny) {
+; CHECK-LABEL: IsPerfect=true, Depth=1, OutermostLoop: test6Loop2, Loops: ( test6Loop2 )
+; CHECK-LABEL: IsPerfect=true, Depth=2, OutermostLoop: test6Loop1, Loops: ( test6Loop1 test6Loop2 )
+entry:
+  %cmp2 = icmp slt i32 0, %nx
+  br i1 %cmp2, label %test6Loop1.lr.ph, label %for.end13
+
+test6Loop1.lr.ph:                                   ; preds = %entry
+  br label %test6Loop1
+
+test6Loop1:                                         ; preds = %test6Loop1.lr.ph, %for.inc11
+  %i.0 = phi i32 [ 0, %test6Loop1.lr.ph ], [ %inc12, %for.inc11 ]
+  %cmp1 = icmp slt i32 %i.0, %ny
+  br i1 %cmp1, label %test6Loop2.lr.ph, label %if.end
+
+test6Loop2.lr.ph:                                  ; preds = %if.then
+  br label %test6Loop2
+
+test6Loop2:                                        ; preds = %test6Loop2.lr.ph, %for.inc
+  %j.0 = phi i32 [ %i.0, %test6Loop2.lr.ph ], [ %inc, %for.inc ]
+  %idxprom = sext i32 %i.0 to i64
+  %arrayidx = getelementptr inbounds i32*, i32** %x, i64 %idxprom
+  %0 = load i32*, i32** %arrayidx, align 8
+  %idxprom5 = sext i32 %j.0 to i64
+  %arrayidx6 = getelementptr inbounds i32, i32* %0, i64 %idxprom5
+  %1 = load i32, i32* %arrayidx6, align 4
+  %add = add nsw i32 %1, %j.0
+  %idxprom7 = sext i32 %j.0 to i64
+  %arrayidx8 = getelementptr inbounds i32*, i32** %y, i64 %idxprom7
+  %2 = load i32*, i32** %arrayidx8, align 8
+  %idxprom9 = sext i32 %i.0 to i64
+  %arrayidx10 = getelementptr inbounds i32, i32* %2, i64 %idxprom9
+  store i32 %add, i32* %arrayidx10, align 4
+  br label %for.inc
+
+for.inc:                                          ; preds = %test6Loop2
+  %inc = add nsw i32 %j.0, 1
+  %cmp3 = icmp slt i32 %inc, %ny
+  br i1 %cmp3, label %test6Loop2, label %for.cond2.for.end_crit_edge
+
+for.cond2.for.end_crit_edge:                      ; preds = %for.inc
+  br label %for.end
+
+for.end:                                          ; preds = %for.cond2.for.end_crit_edge, %if.then
+  br label %if.end
+
+if.end:                                           ; preds = %for.end, %test6Loop1
+  br label %for.inc11
+
+for.inc11:                                        ; preds = %if.end
+  %inc12 = add nsw i32 %i.0, 1
+  %cmp = icmp slt i32 %inc12, %nx
+  br i1 %cmp, label %test6Loop1, label %for.cond.for.end13_crit_edge
+
+for.cond.for.end13_crit_edge:                     ; preds = %for.inc11
+  br label %for.end13
+
+for.end13:                                        ; preds = %for.cond.for.end13_crit_edge, %entry
+  %arrayidx14 = getelementptr inbounds i32*, i32** %y, i64 0
+  %3 = load i32*, i32** %arrayidx14, align 8
+  %arrayidx15 = getelementptr inbounds i32, i32* %3, i64 0
+  %4 = load i32, i32* %arrayidx15, align 4
+  %conv = sitofp i32 %4 to double
+  ret double %conv
+}
+
+; Test a perfect loop nest of the form:
+;   for (int i = 0; i < nx; ++i)
+;     if (i < ny) { // guard branch for the j-loop
+;       for (int j=i; j < ny; j+=1)
+;         y[j][i] = x[i][j] + j;
+;     }
+
+define double @test6(i32** %y, i32** %x, i32 signext %nx, i32 signext %ny) {
+; CHECK-LABEL: IsPerfect=true, Depth=1, OutermostLoop: test6Loop2, Loops: ( test6Loop2 )
+; CHECK-LABEL: IsPerfect=true, Depth=2, OutermostLoop: test6Loop1, Loops: ( test6Loop1 test6Loop2 )
+entry:
+  %cmp2 = icmp slt i32 0, %nx
+  br i1 %cmp2, label %test6Loop1.lr.ph, label %for.end13
+
+test6Loop1.lr.ph:                                   ; preds = %entry
+  br label %test6Loop1
+
+test6Loop1:                                         ; preds = %test6Loop1.lr.ph, %for.inc11
+  %i.0 = phi i32 [ 0, %test6Loop1.lr.ph ], [ %inc12, %for.inc11 ]
+  %cmp1 = icmp slt i32 %i.0, %ny
+  br i1 %cmp1, label %test6Loop2.lr.ph, label %if.end
+
+test6Loop2.lr.ph:                                  ; preds = %if.then
+  br label %test6Loop2
+
+test6Loop2:                                        ; preds = %test6Loop2.lr.ph, %for.inc
+  %j.0 = phi i32 [ %i.0, %test6Loop2.lr.ph ], [ %inc, %for.inc ]
+  %idxprom = sext i32 %i.0 to i64
+  %arrayidx = getelementptr inbounds i32*, i32** %x, i64 %idxprom
+  %0 = load i32*, i32** %arrayidx, align 8
+  %idxprom5 = sext i32 %j.0 to i64
+  %arrayidx6 = getelementptr inbounds i32, i32* %0, i64 %idxprom5
+  %1 = load i32, i32* %arrayidx6, align 4
+  %add = add nsw i32 %1, %j.0
+  %idxprom7 = sext i32 %j.0 to i64
+  %arrayidx8 = getelementptr inbounds i32*, i32** %y, i64 %idxprom7
+  %2 = load i32*, i32** %arrayidx8, align 8
+  %idxprom9 = sext i32 %i.0 to i64
+  %arrayidx10 = getelementptr inbounds i32, i32* %2, i64 %idxprom9
+  store i32 %add, i32* %arrayidx10, align 4
+  br label %for.inc
+
+for.inc:                                          ; preds = %test6Loop2
+  %inc = add nsw i32 %j.0, 1
+  %cmp3 = icmp slt i32 %inc, %ny
+  br i1 %cmp3, label %test6Loop2, label %for.cond2.for.end_crit_edge
+
+for.cond2.for.end_crit_edge:                      ; preds = %for.inc
+  br label %for.end
+
+for.end:                                          ; preds = %for.cond2.for.end_crit_edge, %if.then
+  br label %if.end
+
+if.end:                                           ; preds = %for.end, %test6Loop1
+  br label %for.inc11
+
+for.inc11:                                        ; preds = %if.end
+  %inc12 = add nsw i32 %i.0, 1
+  %cmp = icmp slt i32 %inc12, %nx
+  br i1 %cmp, label %test6Loop1, label %for.cond.for.end13_crit_edge
+
+for.cond.for.end13_crit_edge:                     ; preds = %for.inc11
+  br label %for.end13
+
+for.end13:                                        ; preds = %for.cond.for.end13_crit_edge, %entry
+  %arrayidx14 = getelementptr inbounds i32*, i32** %y, i64 0
+  %3 = load i32*, i32** %arrayidx14, align 8
+  %arrayidx15 = getelementptr inbounds i32, i32* %3, i64 0
+  %4 = load i32, i32* %arrayidx15, align 4
+  %conv = sitofp i32 %4 to double
+  ret double %conv
+}

diff --git a/llvm/unittests/Analysis/LoopInfoTest.cpp b/llvm/unittests/Analysis/LoopInfoTest.cpp
index bb51890..db6484f 100644 (file)
--- a/llvm/unittests/Analysis/LoopInfoTest.cpp
+++ b/llvm/unittests/Analysis/LoopInfoTest.cpp
@@ -1500,3 +1500,51 @@ TEST(LoopInfoTest, LoopNotRotated) {
     EXPECT_FALSE(L->isRotatedForm());
   });
 }
+
+TEST(LoopInfoTest, LoopUserBranch) {
+  const char *ModuleStr =
+      "target datalayout = \"e-m:o-i64:64-f80:128-n8:16:32:64-S128\"\n"
+      "define void @foo(i32* %B, i64 signext %nx, i1 %cond) {\n"
+      "entry:\n"
+      "  br i1 %cond, label %bb, label %guard\n"
+      "guard:\n"
+      "  %cmp.guard = icmp slt i64 0, %nx\n"
+      "  br i1 %cmp.guard, label %for.i.preheader, label %for.end\n"
+      "for.i.preheader:\n"
+      "  br label %for.i\n"
+      "for.i:\n"
+      "  %i = phi i64 [ 0, %for.i.preheader ], [ %inc13, %for.i ]\n"
+      "  %Bi = getelementptr inbounds i32, i32* %B, i64 %i\n"
+      "  store i32 0, i32* %Bi, align 4\n"
+      "  %inc13 = add nsw i64 %i, 1\n"
+      "  %cmp = icmp slt i64 %inc13, %nx\n"
+      "  br i1 %cmp, label %for.i, label %for.i.exit\n"
+      "for.i.exit:\n"
+      "  br label %bb\n"
+      "bb:\n"
+      "  br label %for.end\n"
+      "for.end:\n"
+      "  ret void\n"
+      "}\n";
+
+  // Parse the module.
+  LLVMContext Context;
+  std::unique_ptr<Module> M = makeLLVMModule(Context, ModuleStr);
+
+  runWithLoopInfo(*M, "foo", [&](Function &F, LoopInfo &LI) {
+    Function::iterator FI = F.begin();
+    FI = ++FI;
+    BasicBlock *Guard = &*FI;
+    assert(Guard->getName() == "guard");
+
+    FI = ++FI;
+    BasicBlock *Header = &*(++FI);
+    assert(Header->getName() == "for.i");
+
+    Loop *L = LI.getLoopFor(Header);
+    EXPECT_NE(L, nullptr);
+
+    // L should not have a guard branch
+    EXPECT_EQ(L->getLoopGuardBranch(), nullptr);
+  });
+}