[ValueTracking][ConstantRange] Distinguish low/high always overflow

In order to fold an always overflowing signed saturating add/sub,
we need to know in which direction the always overflow occurs.
This patch splits up AlwaysOverflows into AlwaysOverflowsLow and
AlwaysOverflowsHigh to pass through this information (but it is
not used yet).

Differential Revision: https://reviews.llvm.org/D62463

llvm-svn: 361858

4 files changed, 17 insertions, 14 deletions

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index d46ddc428b2..640063700e8 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -3992,8 +3992,10 @@ static OverflowResult mapOverflowResult(ConstantRange::OverflowResult OR) {
   switch (OR) {
     case ConstantRange::OverflowResult::MayOverflow:
       return OverflowResult::MayOverflow;
-    case ConstantRange::OverflowResult::AlwaysOverflows:
-      return OverflowResult::AlwaysOverflows;
+    case ConstantRange::OverflowResult::AlwaysOverflowsLow:
+      return OverflowResult::AlwaysOverflowsLow;
+    case ConstantRange::OverflowResult::AlwaysOverflowsHigh:
+      return OverflowResult::AlwaysOverflowsHigh;
     case ConstantRange::OverflowResult::NeverOverflows:
       return OverflowResult::NeverOverflows;
   }
diff --git a/llvm/lib/IR/ConstantRange.cpp b/llvm/lib/IR/ConstantRange.cpp
index 0d44c3815b3..30b6a27078c 100644
--- a/llvm/lib/IR/ConstantRange.cpp
+++ b/llvm/lib/IR/ConstantRange.cpp
@@ -1208,9 +1208,9 @@ ConstantRange::OverflowResult ConstantRange::unsignedAddMayOverflow(
   APInt Min = getUnsignedMin(), Max = getUnsignedMax();
   APInt OtherMin = Other.getUnsignedMin(), OtherMax = Other.getUnsignedMax();
 
-  // a u+ b overflows iff a u> ~b.
+  // a u+ b overflows high iff a u> ~b.
   if (Min.ugt(~OtherMin))
-    return OverflowResult::AlwaysOverflows;
+    return OverflowResult::AlwaysOverflowsHigh;
   if (Max.ugt(~OtherMax))
     return OverflowResult::MayOverflow;
   return OverflowResult::NeverOverflows;
@@ -1231,10 +1231,10 @@ ConstantRange::OverflowResult ConstantRange::signedAddMayOverflow(
   // a s+ b overflows low iff a s< 0 && b s< 0 && a s< smin - b.
   if (Min.isNonNegative() && OtherMin.isNonNegative() &&
       Min.sgt(SignedMax - OtherMin))
-    return OverflowResult::AlwaysOverflows;
+    return OverflowResult::AlwaysOverflowsHigh;
   if (Max.isNegative() && OtherMax.isNegative() &&
       Max.slt(SignedMin - OtherMax))
-    return OverflowResult::AlwaysOverflows;
+    return OverflowResult::AlwaysOverflowsLow;
 
   if (Max.isNonNegative() && OtherMax.isNonNegative() &&
       Max.sgt(SignedMax - OtherMax))
@@ -1254,9 +1254,9 @@ ConstantRange::OverflowResult ConstantRange::unsignedSubMayOverflow(
   APInt Min = getUnsignedMin(), Max = getUnsignedMax();
   APInt OtherMin = Other.getUnsignedMin(), OtherMax = Other.getUnsignedMax();
 
-  // a u- b overflows iff a u< b.
+  // a u- b overflows low iff a u< b.
   if (Max.ult(OtherMin))
-    return OverflowResult::AlwaysOverflows;
+    return OverflowResult::AlwaysOverflowsLow;
   if (Min.ult(OtherMax))
     return OverflowResult::MayOverflow;
   return OverflowResult::NeverOverflows;
@@ -1277,10 +1277,10 @@ ConstantRange::OverflowResult ConstantRange::signedSubMayOverflow(
   // a s- b overflows low iff a s< 0 && b s>= 0 && a s< smin + b.
   if (Min.isNonNegative() && OtherMax.isNegative() &&
       Min.sgt(SignedMax + OtherMax))
-    return OverflowResult::AlwaysOverflows;
+    return OverflowResult::AlwaysOverflowsHigh;
   if (Max.isNegative() && OtherMin.isNonNegative() &&
       Max.slt(SignedMin + OtherMin))
-    return OverflowResult::AlwaysOverflows;
+    return OverflowResult::AlwaysOverflowsLow;
 
   if (Max.isNonNegative() && OtherMin.isNegative() &&
       Max.sgt(SignedMax + OtherMin))
@@ -1303,7 +1303,7 @@ ConstantRange::OverflowResult ConstantRange::unsignedMulMayOverflow(
 
   (void) Min.umul_ov(OtherMin, Overflow);
   if (Overflow)
-    return OverflowResult::AlwaysOverflows;
+    return OverflowResult::AlwaysOverflowsHigh;
 
   (void) Max.umul_ov(OtherMax, Overflow);
   if (Overflow)
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index e2813f9d9d4..a18043ef33f 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -2064,7 +2064,7 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
       OR = computeOverflowForUnsignedAdd(Arg0, Arg1, II);
       if (OR == OverflowResult::NeverOverflows)
         return BinaryOperator::CreateNUWAdd(Arg0, Arg1);
-      if (OR == OverflowResult::AlwaysOverflows)
+      if (OR == OverflowResult::AlwaysOverflowsHigh)
         return replaceInstUsesWith(*II,
                                    ConstantInt::getAllOnesValue(II->getType()));
       break;
@@ -2072,7 +2072,7 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
       OR = computeOverflowForUnsignedSub(Arg0, Arg1, II);
       if (OR == OverflowResult::NeverOverflows)
         return BinaryOperator::CreateNUWSub(Arg0, Arg1);
-      if (OR == OverflowResult::AlwaysOverflows)
+      if (OR == OverflowResult::AlwaysOverflowsLow)
         return replaceInstUsesWith(*II,
                                    ConstantInt::getNullValue(II->getType()));
       break;
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index ab2da177d7b..b3eb75ea8a8 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -3993,7 +3993,8 @@ bool InstCombiner::OptimizeOverflowCheck(
   switch (computeOverflow(BinaryOp, IsSigned, LHS, RHS, &OrigI)) {
     case OverflowResult::MayOverflow:
       return false;
-    case OverflowResult::AlwaysOverflows:
+    case OverflowResult::AlwaysOverflowsLow:
+    case OverflowResult::AlwaysOverflowsHigh:
       Result = Builder.CreateBinOp(BinaryOp, LHS, RHS);
       Result->takeName(&OrigI);
       Overflow = Builder.getTrue();