[InstCombine] Ensure that truncated int types are legal.

[bryant]

Summary

Fixes the FIXMEs in D25952 and rL285075.

[bryant]

Retain note in icmp_shl17 since it won't be touched by D25913.

[spatel]

LGTM.

I forgot to ask: do you want to be credited as "bryant" or a different name when we commit this?

[bryant]

In D25955#578847, @spatel wrote:

LGTM.

I forgot to ask: do you want to be credited as "bryant" or a different name when we commit this?

Yes, that would work.

[bryant]

In D25955#578847, @spatel wrote:

LGTM.

I forgot to ask: do you want to be credited as "bryant" or a different name when we commit this?

"bryant" is fine.

lib/Transforms/InstCombine/InstCombineCompares.cpp

if (Shl->hasOneUse() && isSignBitCheck(Pred, *C, TrueIfSigned)) {
     Constant *Mask = ConstantInt::get(
         X->getType(),
         APInt::getOneBitSet(TypeBits, TypeBits - ShiftAmt->getZExtValue() - 1));
     Value *And = Builder->CreateAnd(X, Mask, Shl->getName() + ".mask");
     return new ICmpInst(TrueIfSigned ? ICmpInst::ICMP_NE : ICmpInst::ICMP_EQ,
                         And, Constant::getNullValue(And->getType()));
   }
 
-  // FIXME: This transform can create illegal types. Use the DataLayout to
-  // decide when to try this?
-
   // 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) {
+  if (Shl->hasOneUse() && Amt != 0 && C->countTrailingZeros() >= Amt &&
+      DL.isLegalInteger(TypeBits - Amt)) {
     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);
   }
 

test/Transforms/InstCombine/icmp-shl-zext-simplify.ll

 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
 ; RUN: opt %s -instcombine -S | FileCheck %s
 
 define i1 @icmp_ugt_32(i64) {
 ; CHECK-LABEL: @icmp_ugt_32(
 ; CHECK-NEXT:    [[C:%.*]] = shl nuw i64 %0, 32
 ; CHECK-NEXT:    [[D:%.*]] = icmp ugt i64 [[C]], 4294967295
 ; CHECK-NEXT:    ret i1 [[D]]
 ;
   %c = shl nuw i64 %0, 32
   %d = icmp ugt i64 %c, 4294967295
   ret i1 %d
 }
 
 define i1 @icmp_ule_64(i128) {
 ; CHECK-LABEL: @icmp_ule_64(
-; CHECK-NEXT:    [[TMP2:%.*]] = trunc i128 %0 to i64
-; CHECK-NEXT:    [[D:%.*]] = icmp eq i64 [[TMP2]], 0
+; CHECK-NEXT:    [[C:%.*]] = shl nuw i128 %0, 64
+; CHECK-NEXT:    [[D:%.*]] = icmp ult i128 [[C]], 18446744073709551616
 ; CHECK-NEXT:    ret i1 [[D]]
 ;
   %c = shl nuw i128 %0, 64
   %d = icmp ule i128 %c, 18446744073709551615
   ret i1 %d
 }
 
 define i1 @icmp_ugt_16(i64) {
 ; CHECK-LABEL: @icmp_ugt_16(
 ; CHECK-NEXT:    [[C:%.*]] = shl nuw i64 %0, 16
 ; CHECK-NEXT:    [[D:%.*]] = icmp ugt i64 [[C]], 1048575
 ; CHECK-NEXT:    ret i1 [[D]]
 ;
   %c = shl nuw i64 %0, 16
   %d = icmp ugt i64 %c, 1048575 ; 0x0f_ffff
   ret i1 %d
 }
 
-; FIXME: InstCombine ought not to emit the potentially illegal i48.
 define <2 x i1> @icmp_ule_16x2(<2 x i64>) {
 ; CHECK-LABEL: @icmp_ule_16x2(
-; CHECK-NEXT:    [[TMP2:%.*]] = trunc <2 x i64> %0 to <2 x i48>
-; CHECK-NEXT:    [[D:%.*]] = icmp eq <2 x i48> [[TMP2]], zeroinitializer
+; CHECK-NEXT:    [[C:%.*]] = shl nuw <2 x i64> %0, <i64 16, i64 16>
+; CHECK-NEXT:    [[D:%.*]] = icmp ult <2 x i64> [[C]], <i64 65536, i64 65536>
 ; CHECK-NEXT:    ret <2 x i1> [[D]]
 ;
   %c = shl nuw <2 x i64> %0, <i64 16, i64 16>
   %d = icmp ule <2 x i64> %c, <i64 65535, i64 65535>
   ret <2 x i1> %d
 }
 
 define i1 @icmp_ult_8(i64) {

test/Transforms/InstCombine/icmp.ll

 ; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i16 [[TMP1]], 36
 ; CHECK-NEXT:    ret i1 [[CMP]]
 ;
   %shl = shl i32 %x, 16
   %cmp = icmp slt i32 %shl, 2359296
   ret i1 %cmp
 }
 
-; FIXME: We shouldn't be creating illegal types like i15 in InstCombine.
-
 define i1 @icmp_shl17(i32 %x) {
 ; CHECK-LABEL: @icmp_shl17(
-; CHECK-NEXT:    [[TMP1:%.*]] = trunc i32 %x to i15
-; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i15 [[TMP1]], 18
+; CHECK-NEXT:    [[SHL:%.*]] = shl i32 %x, 17
+; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i32 [[SHL]], 2359296
 ; CHECK-NEXT:    ret i1 [[CMP]]
 ;
   %shl = shl i32 %x, 17
   %cmp = icmp slt i32 %shl, 2359296
   ret i1 %cmp
 }
 
 define <2 x i1> @icmp_shl16_vec(<2 x i32> %x) {