[llvm] r186215 - LFTR improvement to avoid truncation.

[Andrew Trick]

Author: atrick
Date: Fri Jul 12 17:08:48 2013
New Revision: 186215

URL: http://llvm.org/viewvc/llvm-project?rev=186215&view=rev
Log:
LFTR improvement to avoid truncation.

This is a reimplemntation of the patch originally in r186107.

Added:
    llvm/trunk/test/Transforms/IndVarSimplify/lftr-extend-const.ll
Modified:
    llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp

Modified: llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp?rev=186215&r1=186214&r2=186215&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp Fri Jul 12 17:08:48 2013
@@ -1590,15 +1590,41 @@ LinearFunctionTestReplace(Loop *L,
                << "      RHS:\t" << *ExitCnt << "\n"
                << "  IVCount:\t" << *IVCount << "\n");
 
+  IRBuilder<> Builder(BI);
+
   // LFTR can ignore IV overflow and truncate to the width of
   // BECount. This avoids materializing the add(zext(add)) expression.
-  IRBuilder<> Builder(BI);
-  if (SE->getTypeSizeInBits(CmpIndVar->getType())
-      > SE->getTypeSizeInBits(ExitCnt->getType())) {
-    CmpIndVar = Builder.CreateTrunc(CmpIndVar, ExitCnt->getType(),
-                                    "lftr.wideiv");
-  }
+  unsigned CmpIndVarSize = SE->getTypeSizeInBits(CmpIndVar->getType());
+  unsigned ExitCntSize = SE->getTypeSizeInBits(ExitCnt->getType());
+  if (CmpIndVarSize > ExitCntSize) {
+    const SCEVAddRecExpr *AR = cast<SCEVAddRecExpr>(SE->getSCEV(IndVar));
+    const SCEV *ARStart = AR->getStart();
+    const SCEV *ARStep = AR->getStepRecurrence(*SE);
+    // For constant IVCount, avoid truncation.
+    if (isa<SCEVConstant>(ARStart) && isa<SCEVConstant>(IVCount)) {
+      const APInt &Start = cast<SCEVConstant>(ARStart)->getValue()->getValue();
+      APInt Count = cast<SCEVConstant>(IVCount)->getValue()->getValue();
+      // Note that the post-inc value of BackedgeTakenCount may have overflowed
+      // above such that IVCount is now zero.
+      if (IVCount != BackedgeTakenCount && Count == 0) {
+        Count = APInt::getMaxValue(Count.getBitWidth()).zext(CmpIndVarSize);
+        ++Count;
+      }
+      else
+        Count = Count.zext(CmpIndVarSize);
+      APInt NewLimit;
+      if (cast<SCEVConstant>(ARStep)->getValue()->isNegative())
+        NewLimit = Start - Count;
+      else
+        NewLimit = Start + Count;
+      ExitCnt = ConstantInt::get(CmpIndVar->getType(), NewLimit);
 
+      DEBUG(dbgs() << "  Widen RHS:\t" << *ExitCnt << "\n");
+    } else {
+      CmpIndVar = Builder.CreateTrunc(CmpIndVar, ExitCnt->getType(),
+                                      "lftr.wideiv");
+    }
+  }
   Value *Cond = Builder.CreateICmp(P, CmpIndVar, ExitCnt, "exitcond");
   Value *OrigCond = BI->getCondition();
   // It's tempting to use replaceAllUsesWith here to fully replace the old

Added: llvm/trunk/test/Transforms/IndVarSimplify/lftr-extend-const.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/IndVarSimplify/lftr-extend-const.ll?rev=186215&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/IndVarSimplify/lftr-extend-const.ll (added)
+++ llvm/trunk/test/Transforms/IndVarSimplify/lftr-extend-const.ll Fri Jul 12 17:08:48 2013
@@ -0,0 +1,44 @@
+;RUN: opt -S %s -indvars | FileCheck %s
+
+; CHECK-LABEL: @foo
+; CHECK-NOT: %lftr.wideiv = trunc i32 %indvars.iv.next to i16
+; CHECK: %exitcond = icmp ne i32 %indvars.iv.next, 512
+define void @foo() #0 {
+entry:
+  br label %for.body
+
+for.body:                                         ; preds = %entry, %for.body
+  %i.01 = phi i16 [ 0, %entry ], [ %inc, %for.body ]
+  %conv2 = sext i16 %i.01 to i32
+  call void @bar(i32 %conv2) #1
+  %inc = add i16 %i.01, 1
+  %cmp = icmp slt i16 %inc, 512
+  br i1 %cmp, label %for.body, label %for.end
+
+for.end:                                          ; preds = %for.body
+  ret void
+}
+
+; Check that post-incrementing the backedge taken count does not overflow.
+; CHECK-LABEL: @postinc
+; CHECK: icmp eq i32 %indvars.iv.next, 256
+define i32 @postinc() #0 {
+entry:
+  br label %do.body
+
+do.body:                                          ; preds = %do.body, %entry
+  %first.0 = phi i8 [ 0, %entry ], [ %inc, %do.body ]
+  %conv = zext i8 %first.0 to i32
+  call void  @bar(i32 %conv) #1
+  %inc = add i8 %first.0, 1
+  %cmp = icmp eq i8 %first.0, -1
+  br i1 %cmp, label %do.end, label %do.body
+
+do.end:                                           ; preds = %do.body
+  ret i32 0
+}
+
+declare void @bar(i32)
+
+attributes #0 = { nounwind uwtable }
+attributes #1 = { nounwind }