[llvm] r186152 - Revert "indvars: Improve LFTR by eliminating truncation when comparing

[Chandler Carruth]

Author: chandlerc
Date: Fri Jul 12 06:18:55 2013
New Revision: 186152

URL: http://llvm.org/viewvc/llvm-project?rev=186152&view=rev
Log:
Revert "indvars: Improve LFTR by eliminating truncation when comparing
against a constant."

This reverts commit r186107. It didn't handle wrapping arithmetic in the
loop correctly and thus caused the following C program to count from
0 to UINT64_MAX instead of from 0 to 255 as intended:

  #include <stdio.h>
  int main() {
    unsigned char first = 0, last = 255;
    do { printf("%d\n", first); } while (first++ != last);
  }

Full test case and instructions to reproduce with just the -indvars pass
sent to the original review thread rather than to r186107's commit.

Removed:
    llvm/trunk/test/Transforms/IndVarSimplify/exitcnt-const-arstart-const-opt.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=186152&r1=186151&r2=186152&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp Fri Jul 12 06:18:55 2013
@@ -1612,29 +1612,10 @@ LinearFunctionTestReplace(Loop *L,
                << "  IVCount:\t" << *IVCount << "\n");
 
   IRBuilder<> Builder(BI);
-
-  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");
-    }
+  if (SE->getTypeSizeInBits(CmpIndVar->getType())
+      > SE->getTypeSizeInBits(ExitCnt->getType())) {
+    CmpIndVar = Builder.CreateTrunc(CmpIndVar, ExitCnt->getType(),
+                                    "lftr.wideiv");
   }
 
   Value *Cond = Builder.CreateICmp(P, CmpIndVar, ExitCnt, "exitcond");

Removed: llvm/trunk/test/Transforms/IndVarSimplify/exitcnt-const-arstart-const-opt.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/IndVarSimplify/exitcnt-const-arstart-const-opt.ll?rev=186151&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/IndVarSimplify/exitcnt-const-arstart-const-opt.ll (original)
+++ llvm/trunk/test/Transforms/IndVarSimplify/exitcnt-const-arstart-const-opt.ll (removed)
@@ -1,25 +0,0 @@
-;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 }