[InstCombine] canonicalize* LE/GE vector integer comparisons to LT/GT (PR26701, PR26819)

*We don't currently handle the  edge case constants (min/max values), so it's not a complete
canonicalization.

To fully solve the motivating bugs, we need to enhance this to recognize a zero vector
too because that's a ConstantAggregateZero which is a ConstantData, not a ConstantVector
or a ConstantDataVector.

Differential Revision: http://reviews.llvm.org/D17859 

llvm-svn: 269426

3 files changed, 180 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 6ed94cda342..acc03e722f0 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -3125,11 +3125,64 @@ static ICmpInst *canonicalizeCmpWithConstant(ICmpInst &I,
       assert(!Op1C->isMinValue(true));  // A >=s MIN -> TRUE
       return new ICmpInst(ICmpInst::ICMP_SGT, Op0, Builder.getInt(Op1Val - 1));
     default:
-      break;
+      return nullptr;
     }
   }
 
-  // TODO: Handle vectors.
+  // The usual vector types are ConstantDataVector. Exotic vector types are
+  // ConstantVector. They both derive from Constant.
+  if (isa<ConstantDataVector>(Op1) || isa<ConstantVector>(Op1)) {
+    Constant *Op1C = cast<Constant>(Op1);
+    Type *Op1Type = Op1->getType();
+    unsigned NumElts = Op1Type->getVectorNumElements();
+
+    // Set the new comparison predicate and splat a vector of 1 or -1 to
+    // increment or decrement the vector constants. But first, check that no
+    // elements of the constant vector would overflow/underflow when we
+    // increment/decrement the constants.
+    //
+    // TODO? If the edge cases for vectors were guaranteed to be handled as they
+    // are for scalar, we could remove the min/max checks here. However, to do
+    // that, we would have to use insertelement/shufflevector to replace edge
+    // values.
+    
+    CmpInst::Predicate NewPred;
+    Constant *OneOrNegOne = nullptr;
+    switch (I.getPredicate()) {
+    case ICmpInst::ICMP_ULE:
+      for (unsigned i = 0; i != NumElts; ++i)
+        if (cast<ConstantInt>(Op1C->getAggregateElement(i))->isMaxValue(false))
+          return nullptr;
+      NewPred = ICmpInst::ICMP_ULT;
+      OneOrNegOne = ConstantInt::get(Op1Type, 1);
+      break;
+    case ICmpInst::ICMP_SLE:
+      for (unsigned i = 0; i != NumElts; ++i)
+        if (cast<ConstantInt>(Op1C->getAggregateElement(i))->isMaxValue(true))
+          return nullptr;
+      NewPred = ICmpInst::ICMP_SLT;
+      OneOrNegOne = ConstantInt::get(Op1Type, 1);
+      break;
+    case ICmpInst::ICMP_UGE:
+      for (unsigned i = 0; i != NumElts; ++i)
+        if (cast<ConstantInt>(Op1C->getAggregateElement(i))->isMinValue(false))
+          return nullptr;
+      NewPred = ICmpInst::ICMP_UGT;
+      OneOrNegOne = ConstantInt::get(Op1Type, -1);
+      break;
+    case ICmpInst::ICMP_SGE:
+      for (unsigned i = 0; i != NumElts; ++i)
+        if (cast<ConstantInt>(Op1C->getAggregateElement(i))->isMinValue(true))
+          return nullptr;
+      NewPred = ICmpInst::ICMP_SGT;
+      OneOrNegOne = ConstantInt::get(Op1Type, -1);
+      break;
+    default:
+      return nullptr;
+    }
+
+    return new ICmpInst(NewPred, Op0, ConstantExpr::getAdd(Op1C, OneOrNegOne));
+  }
 
   return nullptr;
 }
diff --git a/llvm/test/Transforms/InstCombine/icmp-vec.ll b/llvm/test/Transforms/InstCombine/icmp-vec.ll
new file mode 100644
index 00000000000..f8416cc6e95
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/icmp-vec.ll
@@ -0,0 +1,124 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -instcombine -S | FileCheck %s
+
+; Canonicalize vector ge/le comparisons with constants to gt/lt.
+
+; Normal types are ConstantDataVectors. Test the constant values adjacent to the
+; min/max values that we're not allowed to transform.
+
+define <2 x i1> @sge(<2 x i8> %x) {
+; CHECK-LABEL: @sge(
+; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt <2 x i8> %x, <i8 -128, i8 126>
+; CHECK-NEXT:    ret <2 x i1> [[CMP]]
+;
+  %cmp = icmp sge <2 x i8> %x, <i8 -127, i8 -129>
+  ret <2 x i1> %cmp
+}
+
+define <2 x i1> @uge(<2 x i8> %x) {
+; CHECK-LABEL: @uge(
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ugt <2 x i8> %x, <i8 -2, i8 0>
+; CHECK-NEXT:    ret <2 x i1> [[CMP]]
+;
+  %cmp = icmp uge <2 x i8> %x, <i8 -1, i8 1>
+  ret <2 x i1> %cmp
+}
+
+define <2 x i1> @sle(<2 x i8> %x) {
+; CHECK-LABEL: @sle(
+; CHECK-NEXT:    [[CMP:%.*]] = icmp slt <2 x i8> %x, <i8 127, i8 -127>
+; CHECK-NEXT:    ret <2 x i1> [[CMP]]
+;
+  %cmp = icmp sle <2 x i8> %x, <i8 126, i8 128>
+  ret <2 x i1> %cmp
+}
+
+define <2 x i1> @ule(<2 x i8> %x) {
+; CHECK-LABEL: @ule(
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ult <2 x i8> %x, <i8 -1, i8 1>
+; CHECK-NEXT:    ret <2 x i1> [[CMP]]
+;
+  %cmp = icmp ule <2 x i8> %x, <i8 254, i8 0>
+  ret <2 x i1> %cmp
+}
+
+; Weird types are ConstantVectors, not ConstantDataVectors. For an i3 type:
+; Signed min = -4
+; Unsigned min = 0
+; Signed max = 3
+; Unsigned max = 7
+
+define <3 x i1> @sge_weird(<3 x i3> %x) {
+; CHECK-LABEL: @sge_weird(
+; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt <3 x i3> %x, <i3 -4, i3 2, i3 -1>
+; CHECK-NEXT:    ret <3 x i1> [[CMP]]
+;
+  %cmp = icmp sge <3 x i3> %x, <i3 -3, i3 -5, i3 0>
+  ret <3 x i1> %cmp
+}
+
+define <3 x i1> @uge_weird(<3 x i3> %x) {
+; CHECK-LABEL: @uge_weird(
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ugt <3 x i3> %x, <i3 -2, i3 0, i3 1>
+; CHECK-NEXT:    ret <3 x i1> [[CMP]]
+;
+  %cmp = icmp uge <3 x i3> %x, <i3 -1, i3 1, i3 2>
+  ret <3 x i1> %cmp
+}
+
+define <3 x i1> @sle_weird(<3 x i3> %x) {
+; CHECK-LABEL: @sle_weird(
+; CHECK-NEXT:    [[CMP:%.*]] = icmp slt <3 x i3> %x, <i3 3, i3 -3, i3 1>
+; CHECK-NEXT:    ret <3 x i1> [[CMP]]
+;
+  %cmp = icmp sle <3 x i3> %x, <i3 2, i3 4, i3 0>
+  ret <3 x i1> %cmp
+}
+
+define <3 x i1> @ule_weird(<3 x i3> %x) {
+; CHECK-LABEL: @ule_weird(
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ult <3 x i3> %x, <i3 -1, i3 1, i3 2>
+; CHECK-NEXT:    ret <3 x i1> [[CMP]]
+;
+  %cmp = icmp ule <3 x i3> %x, <i3 6, i3 0, i3 1>
+  ret <3 x i1> %cmp
+}
+
+; We can't do the transform if any constants are already at the limits.
+
+define <2 x i1> @sge_min(<2 x i3> %x) {
+; CHECK-LABEL: @sge_min(
+; CHECK-NEXT:    [[CMP:%.*]] = icmp sge <2 x i3> %x, <i3 -4, i3 1>
+; CHECK-NEXT:    ret <2 x i1> [[CMP]]
+;
+  %cmp = icmp sge <2 x i3> %x, <i3 -4, i3 1>
+  ret <2 x i1> %cmp
+}
+
+define <2 x i1> @uge_min(<2 x i3> %x) {
+; CHECK-LABEL: @uge_min(
+; CHECK-NEXT:    [[CMP:%.*]] = icmp uge <2 x i3> %x, <i3 1, i3 0>
+; CHECK-NEXT:    ret <2 x i1> [[CMP]]
+;
+  %cmp = icmp uge <2 x i3> %x, <i3 1, i3 0>
+  ret <2 x i1> %cmp
+}
+
+define <2 x i1> @sle_max(<2 x i3> %x) {
+; CHECK-LABEL: @sle_max(
+; CHECK-NEXT:    [[CMP:%.*]] = icmp sle <2 x i3> %x, <i3 1, i3 3>
+; CHECK-NEXT:    ret <2 x i1> [[CMP]]
+;
+  %cmp = icmp sle <2 x i3> %x, <i3 1, i3 3>
+  ret <2 x i1> %cmp
+}
+
+define <2 x i1> @ule_max(<2 x i3> %x) {
+; CHECK-LABEL: @ule_max(
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ule <2 x i3> %x, <i3 -1, i3 1>
+; CHECK-NEXT:    ret <2 x i1> [[CMP]]
+;
+  %cmp = icmp ule <2 x i3> %x, <i3 7, i3 1>
+  ret <2 x i1> %cmp
+}
+
diff --git a/llvm/test/Transforms/LoopVectorize/if-conversion.ll b/llvm/test/Transforms/LoopVectorize/if-conversion.ll
index fb541697652..daa8f147e21 100644
--- a/llvm/test/Transforms/LoopVectorize/if-conversion.ll
+++ b/llvm/test/Transforms/LoopVectorize/if-conversion.ll
@@ -73,7 +73,7 @@ for.end:
 ;CHECK-LABEL: @reduction_func(
 ;CHECK: load <4 x i32>
 ;CHECK: add <4 x i32>
-;CHECK: icmp sle <4 x i32>
+;CHECK: icmp slt <4 x i32>
 ;CHECK: select <4 x i1>
 ;CHECK: ret i32
 define i32 @reduction_func(i32* nocapture %A, i32 %n) nounwind uwtable readonly ssp {