[PATCH] Little improvement in IndVarSimplify

[Michele Scandale]

  Here an updated version of the patch fixing code style as suggested by Andrew.

  Thanks again.

  Michele Scandale

Hi atrick,

http://llvm-reviews.chandlerc.com/D1112

CHANGE SINCE LAST DIFF
  http://llvm-reviews.chandlerc.com/D1112?vs=2713&id=2765#toc

Files:
  lib/Transforms/Scalar/IndVarSimplify.cpp
  test/Transforms/IndVarSimplify/exitcnt-const-arstart-const-opt.ll

Index: lib/Transforms/Scalar/IndVarSimplify.cpp
===================================================================
--- lib/Transforms/Scalar/IndVarSimplify.cpp
+++ lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -1612,10 +1612,29 @@
                << "  IVCount:\t" << *IVCount << "\n");
 
   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);
+    if (isa<SCEVConstant>(ARStart) && isa<SCEVConstant>(IVCount)) {
+      const APInt &Start = cast<SCEVConstant>(ARStart)->getValue()->getValue();
+      const APInt &Count = cast<SCEVConstant>(IVCount)->getValue()->getValue();
+
+      APInt NewLimit;
+      if (cast<SCEVConstant>(ARStep)->getValue()->isNegative())
+        NewLimit = Start - Count.zext(CmpIndVarSize);
+      else
+        NewLimit = Start + Count.zext(CmpIndVarSize);
+      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");
Index: test/Transforms/IndVarSimplify/exitcnt-const-arstart-const-opt.ll
===================================================================
--- test/Transforms/IndVarSimplify/exitcnt-const-arstart-const-opt.ll
+++ test/Transforms/IndVarSimplify/exitcnt-const-arstart-const-opt.ll
@@ -0,0 +1,25 @@
+;RUN: opt -S %s -indvars | FileCheck %s
+
+; Function Attrs: nounwind uwtable
+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
+;CHECK-NOT: %lftr.wideiv = trunc i32 %indvars.iv.next to i16
+;CHECK: %exitcond = icmp ne i32 %indvars.iv.next, 512
+  %cmp = icmp slt i16 %inc, 512
+  br i1 %cmp, label %for.body, label %for.end
+
+for.end:                                          ; preds = %for.body
+  ret void
+}
+
+declare void @bar(i32)
+
+attributes #0 = { nounwind uwtable }
+attributes #1 = { nounwind }
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