[PATCH] D23075: [IndVarSimplify] Extend trip count instead of truncating IV in LFTR, when original IV does not overflow

[Ehsan Amiri via llvm-commits]

amehsan updated this revision to Diff 67013.
amehsan added a comment.

As Sanjoy proposed, I changed the implementation to rely on SCEV to prove legality of extending trip count.


https://reviews.llvm.org/D23075

Files:
  lib/Transforms/Scalar/IndVarSimplify.cpp
  test/Transforms/IndVarSimplify/elim-extend.ll
  test/Transforms/IndVarSimplify/promote-iv-to-eliminate-casts.ll
  test/Transforms/IndVarSimplify/signed-trip-count.ll
  test/Transforms/IndVarSimplify/ult-sub-to-eq.ll

Index: test/Transforms/IndVarSimplify/ult-sub-to-eq.ll
===================================================================
--- test/Transforms/IndVarSimplify/ult-sub-to-eq.ll
+++ test/Transforms/IndVarSimplify/ult-sub-to-eq.ll
@@ -33,8 +33,9 @@
 ; CHECK-LABEL: @test1(
 
 ; check that we turn the IV test into an eq.
-; CHECK: %lftr.wideiv = trunc i64 %indvars.iv.next to i32
-; CHECK: %exitcond = icmp ne i32 %lftr.wideiv, %sub
+; CHECK: %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+; CHECK: %wide.trip.count = zext i32 %sub to i64
+; CHECK: %exitcond = icmp ne i64 %indvars.iv.next, %wide.trip.count
 ; CHECK: br i1 %exitcond, label %for.body, label %for.end.loopexit
 }
 
Index: test/Transforms/IndVarSimplify/signed-trip-count.ll
===================================================================
--- test/Transforms/IndVarSimplify/signed-trip-count.ll
+++ test/Transforms/IndVarSimplify/signed-trip-count.ll
@@ -1,4 +1,4 @@
-; RUN: opt < %s -indvars -S > %t
+; RUN: opt < %s -indvars -S | grep -v wide.trip.count > %t
 ; RUN: not grep sext %t
 ; RUN: grep phi %t | count 1
 
Index: test/Transforms/IndVarSimplify/promote-iv-to-eliminate-casts.ll
===================================================================
--- test/Transforms/IndVarSimplify/promote-iv-to-eliminate-casts.ll
+++ test/Transforms/IndVarSimplify/promote-iv-to-eliminate-casts.ll
@@ -1,4 +1,4 @@
-; RUN: opt < %s -indvars -S | not grep sext
+; RUN: opt < %s -indvars -S | grep -v wide.trip.count | not grep sext
 
 ; Provide legal integer types.
 target datalayout = "n8:16:32:64"
Index: test/Transforms/IndVarSimplify/elim-extend.ll
===================================================================
--- test/Transforms/IndVarSimplify/elim-extend.ll
+++ test/Transforms/IndVarSimplify/elim-extend.ll
@@ -41,6 +41,8 @@
   br i1 %precond, label %loop, label %return
 ; CHECK: loop:
 ; CHECK-NOT: sext
+; CHECK: wide.trip.count = sext
+; CHECK-NOT: sext
 ; CHECK: exit:
 loop:
   %iv = phi i32 [ %postiv, %loop ], [ %init, %entry ]
Index: lib/Transforms/Scalar/IndVarSimplify.cpp
===================================================================
--- lib/Transforms/Scalar/IndVarSimplify.cpp
+++ lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -1984,8 +1984,33 @@
 
       DEBUG(dbgs() << "  Widen RHS:\t" << *ExitCnt << "\n");
     } else {
-      CmpIndVar = Builder.CreateTrunc(CmpIndVar, ExitCnt->getType(),
-                                      "lftr.wideiv");
+      bool Extended = false;
+      const SCEV *IV = SE->getSCEV(CmpIndVar);
+      const SCEV *ZExTrunc =
+           SE->getZeroExtendExpr(SE->getTruncateExpr(SE->getSCEV(CmpIndVar),
+                                                     ExitCnt->getType()),
+                                 CmpIndVar->getType());
+
+      if (ZExTrunc == IV) {
+        Extended = true;
+        ExitCnt = Builder.CreateZExt(ExitCnt, IndVar->getType(),
+                                     "wide.trip.count");
+      } else {
+        const SCEV *SExTrunc =
+          SE->getSignExtendExpr(SE->getTruncateExpr(SE->getSCEV(CmpIndVar),
+                                                    ExitCnt->getType()),
+                                CmpIndVar->getType());
+        if (SExTrunc == IV) {
+          Extended = true;
+          ExitCnt = Builder.CreateSExt(ExitCnt, IndVar->getType(),
+                                       "wide.trip.count");
+        }
+      }
+
+      if (!Extended) {
+        CmpIndVar = Builder.CreateTrunc(CmpIndVar, ExitCnt->getType(),
+                                        "lftr.wideiv");
+      }
     }
   }
   Value *Cond = Builder.CreateICmp(P, CmpIndVar, ExitCnt, "exitcond");


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