From: Richard Trieu <rtrieu@google.com>
Date: Thu, 5 Nov 2015 23:20:36 +0000 (+0000)
Subject: Revert r251050 to fix miscompile when running Clang -O1
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=59970e6f528230b1d97a95facc5c4a281dcc2535;p=oota-llvm.git

Revert r251050 to fix miscompile when running Clang -O1

See bug for details: https://llvm.org/bugs/show_bug.cgi?id=25421
Some comparisons were incorrectly replaced with a constant value.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@252231 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/include/llvm/Analysis/ScalarEvolution.h b/include/llvm/Analysis/ScalarEvolution.h
index c180ce37e39..65125a7da5e 100644
--- a/include/llvm/Analysis/ScalarEvolution.h
+++ b/include/llvm/Analysis/ScalarEvolution.h
@@ -732,14 +732,6 @@ namespace llvm {
     bool isKnownPredicateWithRanges(ICmpInst::Predicate Pred,
                                     const SCEV *LHS, const SCEV *RHS);
 
-    /// Try to prove the condition described by "LHS Pred RHS" by ruling out
-    /// integer overflow.
-    ///
-    /// For instance, this will return true for "A s< (A + C)<nsw>" if C is
-    /// positive.
-    bool isKnownPredicateViaNoOverflow(ICmpInst::Predicate Pred,
-                                       const SCEV *LHS, const SCEV *RHS);
-
     /// Try to split Pred LHS RHS into logical conjunctions (and's) and try to
     /// prove them individually.
     bool isKnownPredicateViaSplitting(ICmpInst::Predicate Pred, const SCEV *LHS,
diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp
index 0d4a62c9d80..4652e449f4b 100644
--- a/lib/Analysis/ScalarEvolution.cpp
+++ b/lib/Analysis/ScalarEvolution.cpp
@@ -7348,60 +7348,6 @@ ScalarEvolution::isKnownPredicateWithRanges(ICmpInst::Predicate Pred,
   return false;
 }
 
-bool ScalarEvolution::isKnownPredicateViaNoOverflow(ICmpInst::Predicate Pred,
-                                                    const SCEV *LHS,
-                                                    const SCEV *RHS) {
-
-  // Match Result to (X + Y)<ExpectedFlags> where Y is a constant integer.
-  // Return Y via OutY.
-  auto MatchBinaryAddToConst =
-      [this](const SCEV *Result, const SCEV *X, APInt &OutY,
-             SCEV::NoWrapFlags ExpectedFlags) {
-    const SCEV *NonConstOp, *ConstOp;
-    SCEV::NoWrapFlags FlagsPresent;
-
-    if (!splitBinaryAdd(Result, ConstOp, NonConstOp, FlagsPresent) ||
-        !isa<SCEVConstant>(ConstOp) || NonConstOp != X)
-      return false;
-
-    OutY = cast<SCEVConstant>(ConstOp)->getValue()->getValue();
-    return (FlagsPresent & ExpectedFlags) == ExpectedFlags;
-  };
-
-  APInt C;
-
-  switch (Pred) {
-  default:
-    break;
-
-  case ICmpInst::ICMP_SGE:
-    std::swap(LHS, RHS);
-  case ICmpInst::ICMP_SLE:
-    // X s<= (X + C)<nsw> if C >= 0
-    if (MatchBinaryAddToConst(RHS, LHS, C, SCEV::FlagNSW) && C.isNonNegative())
-      return true;
-
-    // (X + C)<nsw> s<= X if C <= 0
-    if (MatchBinaryAddToConst(LHS, RHS, C, SCEV::FlagNSW) &&
-        !C.isStrictlyPositive())
-      return true;
-
-  case ICmpInst::ICMP_SGT:
-    std::swap(LHS, RHS);
-  case ICmpInst::ICMP_SLT:
-    // X s< (X + C)<nsw> if C > 0
-    if (MatchBinaryAddToConst(RHS, LHS, C, SCEV::FlagNSW) &&
-        C.isStrictlyPositive())
-      return true;
-
-    // (X + C)<nsw> s< X if C < 0
-    if (MatchBinaryAddToConst(LHS, RHS, C, SCEV::FlagNSW) && C.isNegative())
-      return true;
-  }
-
-  return false;
-}
-
 bool ScalarEvolution::isKnownPredicateViaSplitting(ICmpInst::Predicate Pred,
                                                    const SCEV *LHS,
                                                    const SCEV *RHS) {
@@ -8058,8 +8004,7 @@ ScalarEvolution::isImpliedCondOperandsHelper(ICmpInst::Predicate Pred,
       [this](ICmpInst::Predicate Pred, const SCEV *LHS, const SCEV *RHS) {
     return isKnownPredicateWithRanges(Pred, LHS, RHS) ||
            IsKnownPredicateViaMinOrMax(*this, Pred, LHS, RHS) ||
-           IsKnownPredicateViaAddRecStart(*this, Pred, LHS, RHS) ||
-           isKnownPredicateViaNoOverflow(Pred, LHS, RHS);
+           IsKnownPredicateViaAddRecStart(*this, Pred, LHS, RHS);
   };
 
   switch (Pred) {
diff --git a/test/Transforms/IndVarSimplify/eliminate-comparison.ll b/test/Transforms/IndVarSimplify/eliminate-comparison.ll
index 612f01e3cad..89f625111d4 100644
--- a/test/Transforms/IndVarSimplify/eliminate-comparison.ll
+++ b/test/Transforms/IndVarSimplify/eliminate-comparison.ll
@@ -447,64 +447,6 @@ define void @func_20(i32* %length.ptr) {
   ret void
 }
 
-define void @func_21(i32* %length.ptr) {
-; CHECK-LABEL: @func_21(
-
-; This checks that the backedge condition, (I + 1) < Length - 1 implies
-; (I + 1) < Length
- entry:
-  %length = load i32, i32* %length.ptr, !range !0
-  %lim = sub i32 %length, 1
-  %entry.cond = icmp sgt i32 %length, 1
-  br i1 %entry.cond, label %loop, label %leave
-
- loop:
-; CHECK: loop:
-  %iv = phi i32 [ 0, %entry ], [ %iv.inc, %be ]
-  %iv.inc = add i32 %iv, 1
-  %range.check = icmp slt i32 %iv, %length
-  br i1 %range.check, label %be, label %leave
-; CHECK:   br i1 true, label %be, label %leave.loopexit
-; CHECK: be:
-
- be:
-  call void @side_effect()
-  %be.cond = icmp slt i32 %iv.inc, %lim
-  br i1 %be.cond, label %loop, label %leave
-
- leave:
-  ret void
-}
-
-define void @func_22(i32* %length.ptr) {
-; CHECK-LABEL: @func_22(
-
-; This checks that the backedge condition, (I + 1) < Length - 1 implies
-; (I + 1) < Length
- entry:
-  %length = load i32, i32* %length.ptr, !range !0
-  %lim = sub i32 %length, 1
-  %entry.cond = icmp sgt i32 %length, 1
-  br i1 %entry.cond, label %loop, label %leave
-
- loop:
-; CHECK: loop:
-  %iv = phi i32 [ 0, %entry ], [ %iv.inc, %be ]
-  %iv.inc = add i32 %iv, 1
-  %range.check = icmp sle i32 %iv, %length
-  br i1 %range.check, label %be, label %leave
-; CHECK:   br i1 true, label %be, label %leave.loopexit
-; CHECK: be:
-
- be:
-  call void @side_effect()
-  %be.cond = icmp sle i32 %iv.inc, %lim
-  br i1 %be.cond, label %loop, label %leave
-
- leave:
-  ret void
-}
-
 define void @func_23(i32* %length.ptr) {
 ; CHECK-LABEL: @func_23(
  entry: