[IRCE] Canonicalize pre/post loops after the blocks are added into parent loop

Summary:
We were canonizalizing the pre loop (into loop-simplify form) before
the post loop blocks were added into parent loop. This is incorrect when IRCE is
done on a subloop. The post-loop blocks are created, but not yet added to the
parent loop. So, loop-simplification on the pre-loop incorrectly updates
LoopInfo.

This patch corrects the ordering so that pre and post loop blocks are added to
parent loop (if any), and then the loops are canonicalized to LCSSA and
LoopSimplifyForm.

Reviewers: reames, sanjoy, apilipenko

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D33846

llvm-svn: 304800

1 files changed, 20 insertions, 13 deletions

diff --git a/llvm/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp b/llvm/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp
index 5017a08ed1e..2f96c3064b8 100644
--- a/llvm/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp
+++ b/llvm/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp
@@ -1371,28 +1371,35 @@ bool LoopConstrainer::run() {
 
   DT.recalculate(F);
 
+  // We need to first add all the pre and post loop blocks into the loop
+  // structures (as part of createClonedLoopStructure), and then update the
+  // LCSSA form and LoopSimplifyForm. This is necessary for correctly updating
+  // LI when LoopSimplifyForm is generated.
+  Loop *PreL = nullptr, *PostL = nullptr;
   if (!PreLoop.Blocks.empty()) {
-    auto *L = createClonedLoopStructure(
+    PreL = createClonedLoopStructure(
         &OriginalLoop, OriginalLoop.getParentLoop(), PreLoop.Map);
-    formLCSSARecursively(*L, DT, &LI, &SE);
-    simplifyLoop(L, &DT, &LI, &SE, nullptr, true);
-    // Pre loops are slow paths, we do not need to perform any loop
-    // optimizations on them.
-    DisableAllLoopOptsOnLoop(*L);
   }
 
   if (!PostLoop.Blocks.empty()) {
-    auto *L = createClonedLoopStructure(
+    PostL = createClonedLoopStructure(
         &OriginalLoop, OriginalLoop.getParentLoop(), PostLoop.Map);
+  }
+
+  // This function canonicalizes the loop into Loop-Simplify and LCSSA forms.
+  auto CanonicalizeLoop = [&] (Loop *L, bool IsOriginalLoop) {
     formLCSSARecursively(*L, DT, &LI, &SE);
     simplifyLoop(L, &DT, &LI, &SE, nullptr, true);
-    // Post loops are slow paths, we do not need to perform any loop
+    // Pre/post loops are slow paths, we do not need to perform any loop
     // optimizations on them.
-    DisableAllLoopOptsOnLoop(*L);
-  }
-
-  formLCSSARecursively(OriginalLoop, DT, &LI, &SE);
-  simplifyLoop(&OriginalLoop, &DT, &LI, &SE, nullptr, true);
+    if (!IsOriginalLoop)
+      DisableAllLoopOptsOnLoop(*L);
+  };
+  if (PreL)
+    CanonicalizeLoop(PreL, false);
+  if (PostL)
+    CanonicalizeLoop(PostL, false);
+  CanonicalizeLoop(&OriginalLoop, true);
 
   return true;
 }