[llvm] r279401 - [InstCombine] use m_APInt to allow icmp (shl X, Y), C folds for splat constant vectors, part 4

[Sanjay Patel via llvm-commits]

Author: spatel
Date: Sun Aug 21 12:10:07 2016
New Revision: 279401

URL: http://llvm.org/viewvc/llvm-project?rev=279401&view=rev
Log:
[InstCombine] use m_APInt to allow icmp (shl X, Y), C folds for splat constant vectors, part 4

This concludes the fixes for icmp+shl in this series:
https://reviews.llvm.org/rL279339
https://reviews.llvm.org/rL279398
https://reviews.llvm.org/rL279399


Modified:
    llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp
    llvm/trunk/test/Transforms/InstCombine/icmp.ll

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp?rev=279401&r1=279400&r2=279401&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp Sun Aug 21 12:10:07 2016
@@ -2042,23 +2042,20 @@ Instruction *InstCombiner::foldICmpShlCo
                         And, Constant::getNullValue(And->getType()));
   }
 
-  // FIXME: This check restricts all folds under here to scalar types.
-  ConstantInt *RHS = dyn_cast<ConstantInt>(Cmp.getOperand(1));
-  if (!RHS)
-    return nullptr;
-
-  // Transform (icmp pred iM (shl iM %v, N), CI)
-  // -> (icmp pred i(M-N) (trunc %v iM to i(M-N)), (trunc (CI>>N))
-  // Transform the shl to a trunc if (trunc (CI>>N)) has no loss and M-N.
-  // This enables to get rid of the shift in favor of a trunc which can be
+  // Transform (icmp pred iM (shl iM %v, N), C)
+  // -> (icmp pred i(M-N) (trunc %v iM to i(M-N)), (trunc (C>>N))
+  // Transform the shl to a trunc if (trunc (C>>N)) has no loss and M-N.
+  // This enables us to get rid of the shift in favor of a trunc which can be
   // free on the target. It has the additional benefit of comparing to a
   // smaller constant, which will be target friendly.
   unsigned Amt = ShiftAmt->getLimitedValue(TypeBits - 1);
   if (Shl->hasOneUse() && Amt != 0 && C->countTrailingZeros() >= Amt) {
-    Type *NTy = IntegerType::get(Cmp.getContext(), TypeBits - Amt);
-    Constant *NCI = ConstantExpr::getTrunc(
-        ConstantExpr::getAShr(RHS, ConstantInt::get(RHS->getType(), Amt)), NTy);
-    return new ICmpInst(Pred, Builder->CreateTrunc(X, NTy), NCI);
+    Type *TruncTy = IntegerType::get(Cmp.getContext(), TypeBits - Amt);
+    if (X->getType()->isVectorTy())
+      TruncTy = VectorType::get(TruncTy, X->getType()->getVectorNumElements());
+    Constant *NewC =
+        ConstantInt::get(TruncTy, C->ashr(*ShiftAmt).trunc(TypeBits - Amt));
+    return new ICmpInst(Pred, Builder->CreateTrunc(X, TruncTy), NewC);
   }
 
   return nullptr;

Modified: llvm/trunk/test/Transforms/InstCombine/icmp.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/icmp.ll?rev=279401&r1=279400&r2=279401&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/icmp.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/icmp.ll Sun Aug 21 12:10:07 2016
@@ -1105,11 +1105,10 @@ define i1 @icmp_shl16(i32 %x) {
   ret i1 %cmp
 }
 
-; FIXME: Vectors should fold the same way.
 define <2 x i1> @icmp_shl16_vec(<2 x i32> %x) {
 ; CHECK-LABEL: @icmp_shl16_vec(
-; CHECK-NEXT:    [[SHL:%.*]] = shl <2 x i32> %x, <i32 16, i32 16>
-; CHECK-NEXT:    [[CMP:%.*]] = icmp slt <2 x i32> [[SHL]], <i32 2359296, i32 2359296>
+; CHECK-NEXT:    [[TMP1:%.*]] = trunc <2 x i32> %x to <2 x i16>
+; CHECK-NEXT:    [[CMP:%.*]] = icmp slt <2 x i16> [[TMP1]], <i16 36, i16 36>
 ; CHECK-NEXT:    ret <2 x i1> [[CMP]]
 ;
   %shl = shl <2 x i32> %x, <i32 16, i32 16>