From: Stelios Ioannou <stelios.ioannou@arm.com>
Date: Tue, 11 May 2021 13:47:19 +0000 (+0100)
Subject: [LoopFlatten] Simplify loops so that the pass can operate on unsimplified loops.
X-Git-Tag: llvmorg-14-init~6888
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=1124ad2f5d47aa468a0d00b6d82853a6d4eda8d1;p=platform%2Fupstream%2Fllvm.git

[LoopFlatten] Simplify loops so that the pass can operate on unsimplified loops.

The loop flattening pass requires loops to be in simplified form. If the
loops are not in simplified form, the pass cannot operate. This patch
simplifies all loops before flattening. As a result, all loops will be
simplified regardless of whether anything ends up being flattened.

This change was inspired by observing a certain loop that was not flatten
because the loops were not in simplified form. This loop is added as a
test to verify that it is now flattened.

Differential Revision: https://reviews.llvm.org/D102249

Change-Id: I45bcabe70fb99b0d89f0effafc82eb9e0585ec30
---

diff --git a/llvm/lib/Transforms/Scalar/LoopFlatten.cpp b/llvm/lib/Transforms/Scalar/LoopFlatten.cpp
index 7dc7cbf..4c5ffdc 100644
--- a/llvm/lib/Transforms/Scalar/LoopFlatten.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopFlatten.cpp
@@ -679,7 +679,23 @@ PreservedAnalyses LoopFlattenPass::run(Function &F,
   auto *AC = &AM.getResult<AssumptionAnalysis>(F);
   auto *TTI = &AM.getResult<TargetIRAnalysis>(F);
 
-  if (!Flatten(DT, LI, SE, AC, TTI))
+  bool Changed = false;
+
+  // The loop flattening pass requires loops to be
+  // in simplified form, and also needs LCSSA. Running
+  // this pass will simplify all loops that contain inner loops,
+  // regardless of whether anything ends up being flattened.
+  for (const auto &L : *LI) {
+    if (L->isInnermost())
+      continue;
+    Changed |=
+        simplifyLoop(L, DT, LI, SE, AC, nullptr, false /* PreserveLCSSA */);
+    Changed |= formLCSSARecursively(*L, *DT, LI, SE);
+  }
+
+  Changed |= Flatten(DT, LI, SE, AC, TTI);
+
+  if (!Changed)
     return PreservedAnalyses::all();
 
   return PreservedAnalyses::none();
diff --git a/llvm/test/Transforms/LoopFlatten/loop-flatten-simplify-cfg.ll b/llvm/test/Transforms/LoopFlatten/loop-flatten-simplify-cfg.ll
new file mode 100644
index 0000000..89487cd
--- /dev/null
+++ b/llvm/test/Transforms/LoopFlatten/loop-flatten-simplify-cfg.ll
@@ -0,0 +1,59 @@
+;; This test was created to ensure that the LoopFlatten pass can
+;; operate on loops that are not in simplified form before applying the pass.
+
+; RUN: opt < %s -S -loop-flatten  -simplifycfg -verify-loop-info -verify-dom-info -verify-scev -verify | FileCheck %s
+
+target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
+
+define void @test(i64 %N, i64* %A, i64 %val) {
+; CHECK-LABEL: @test(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[CMP_NOT:%.*]] = icmp eq i64 [[N:%.*]], 0
+; CHECK-NEXT:    br i1 [[CMP_NOT]], label [[FOR_END:%.*]], label [[FOR_COND_PREHEADER_PREHEADER:%.*]]
+; CHECK:       for.cond.preheader.preheader:
+; CHECK-NEXT:    [[FLATTEN_TRIPCOUNT:%.*]] = mul i64 [[N]], [[N]]
+; CHECK-NEXT:    br label [[FOR_COND_PREHEADER:%.*]]
+; CHECK:       for.cond.preheader:
+; CHECK-NEXT:    [[I:%.*]] = phi i64 [ [[INC6:%.*]], [[FOR_COND_PREHEADER]] ], [ 0, [[FOR_COND_PREHEADER_PREHEADER]] ]
+; CHECK-NEXT:    [[MUL:%.*]] = mul i64 [[I]], [[N]]
+; CHECK-NEXT:    [[ADD:%.*]] = add i64 0, [[MUL]]
+; CHECK-NEXT:    [[ARRAYIDX:%.*]] = getelementptr inbounds i64, i64* [[A:%.*]], i64 [[I]]
+; CHECK-NEXT:    [[TMP0:%.*]] = load i64, i64* [[ARRAYIDX]], align 4
+; CHECK-NEXT:    [[ADD4:%.*]] = add nsw i64 [[TMP0]], [[VAL:%.*]]
+; CHECK-NEXT:    store i64 [[ADD4]], i64* [[ARRAYIDX]], align 4
+; CHECK-NEXT:    [[INC:%.*]] = add nuw nsw i64 0, 1
+; CHECK-NEXT:    [[CMP2:%.*]] = icmp ult i64 [[INC]], [[N]]
+; CHECK-NEXT:    [[INC6]] = add nuw nsw i64 [[I]], 1
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ult i64 [[INC6]], [[FLATTEN_TRIPCOUNT]]
+; CHECK-NEXT:    br i1 [[CMP]], label [[FOR_COND_PREHEADER]], label [[FOR_END]]
+; CHECK:       for.end:
+; CHECK-NEXT:    ret void
+;
+entry:
+  %cmp.not = icmp eq i64 %N, 0
+  br i1 %cmp.not, label %for.end, label %for.cond.preheader
+
+for.cond.preheader:
+  %i= phi i64 [ %inc6, %for.cond.for.inc_crit_edge ], [ 0, %entry ]
+  %mul = mul i64 %i, %N
+  br label %for.body
+
+for.body:
+  %j = phi i64 [ 0, %for.cond.preheader ], [ %inc, %for.body ]
+  %add = add i64 %j, %mul
+  %arrayidx = getelementptr inbounds i64, i64* %A, i64 %add
+  %0 = load i64, i64* %arrayidx, align 4
+  %add4 = add nsw i64 %0, %val
+  store i64 %add4, i64* %arrayidx, align 4
+  %inc = add nuw nsw i64 %j, 1
+  %cmp2 = icmp ult i64 %inc, %N
+  br i1 %cmp2, label %for.body, label %for.cond.for.inc_crit_edge
+
+for.cond.for.inc_crit_edge:
+  %inc6 = add nuw nsw i64 %i, 1
+  %cmp = icmp ult i64 %inc6, %N
+  br i1 %cmp, label %for.cond.preheader, label %for.end
+
+for.end:
+  ret void
+}