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[InstCombine] Optimize (icmp slt (1 << Y), 1) -> (icmp eq Y, BitWidth-1).

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The code tried to do this for (icmp sle (1 << Y), 0), but that is
canonicalized to sgt before we get there.

Simplify the code by removing the unreachable SGE and SLE handling.

Also remove the (1 << Y) >=u 2147483648 and (1 << Y) <u 2147483648
handling since those are canonicalized to (1 << Y) <s 0 and
(1 << Y) >=s 0 before we get there.

Reviewed By: spatel

Differential Revision: https://reviews.llvm.org/D141753
This commit is contained in:
Craig Topper 2023-01-14 11:18:47 -08:00
parent a1580d7b59
commit ff39b7ea89
2 changed files with 12 additions and 30 deletions
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36
llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
View File

@ -2042,37 +2042,21 @@ static Instruction *foldICmpShlOne(ICmpInst &Cmp, Instruction *Shl,
Pred = ICmpInst::ICMP_UGT;
}
// (1 << Y) >= 2147483648 -> Y >= 31 -> Y == 31
// (1 << Y) < 2147483648 -> Y < 31 -> Y != 31
unsigned CLog2 = C.logBase2();
if (CLog2 == TypeBits - 1) {
if (Pred == ICmpInst::ICMP_UGE)
Pred = ICmpInst::ICMP_EQ;
else if (Pred == ICmpInst::ICMP_ULT)
Pred = ICmpInst::ICMP_NE;
}
return new ICmpInst(Pred, Y, ConstantInt::get(ShiftType, CLog2));
} else if (Cmp.isSigned()) {
Constant *BitWidthMinusOne = ConstantInt::get(ShiftType, TypeBits - 1);
if (C.isAllOnes()) {
// (1 << Y) <= -1 -> Y == 31
if (Pred == ICmpInst::ICMP_SLE)
return new ICmpInst(ICmpInst::ICMP_EQ, Y, BitWidthMinusOne);
// (1 << Y) > 0 -> Y != 31
// (1 << Y) > -1 -> Y != 31
// TODO: This can be generalized to any negative constant.
if (Pred == ICmpInst::ICMP_SGT && (C.isZero() || C.isAllOnes()))
return new ICmpInst(ICmpInst::ICMP_NE, Y, BitWidthMinusOne);
// (1 << Y) > -1 -> Y != 31
if (Pred == ICmpInst::ICMP_SGT)
return new ICmpInst(ICmpInst::ICMP_NE, Y, BitWidthMinusOne);
} else if (!C) {
// (1 << Y) < 0 -> Y == 31
// (1 << Y) <= 0 -> Y == 31
if (Pred == ICmpInst::ICMP_SLT || Pred == ICmpInst::ICMP_SLE)
return new ICmpInst(ICmpInst::ICMP_EQ, Y, BitWidthMinusOne);
// (1 << Y) >= 0 -> Y != 31
// (1 << Y) > 0 -> Y != 31
if (Pred == ICmpInst::ICMP_SGT || Pred == ICmpInst::ICMP_SGE)
return new ICmpInst(ICmpInst::ICMP_NE, Y, BitWidthMinusOne);
}
// (1 << Y) < 0 -> Y == 31
// (1 << Y) < 1 -> Y == 31
// TODO: This can be generalized to any negative constant except signed min.
if (Pred == ICmpInst::ICMP_SLT && (C.isZero() || C.isOne()))
return new ICmpInst(ICmpInst::ICMP_EQ, Y, BitWidthMinusOne);
} else if (Cmp.isEquality() && CIsPowerOf2) {
return new ICmpInst(Pred, Y, ConstantInt::get(ShiftType, C.logBase2()));
}

6
llvm/test/Transforms/InstCombine/icmp.ll
View File

@ -2160,8 +2160,7 @@ define <2 x i1> @icmp_shl_1_V_ult_2147483648_vec(<2 x i32> %V) {
define i1 @icmp_shl_1_V_sle_0(i32 %V) {
; CHECK-LABEL: @icmp_shl_1_V_sle_0(
; CHECK-NEXT: [[SHL:%.*]] = shl nuw i32 1, [[V:%.*]]
; CHECK-NEXT: [[CMP:%.*]] = icmp slt i32 [[SHL]], 1
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 [[V:%.*]], 31
; CHECK-NEXT: ret i1 [[CMP]]
;
%shl = shl i32 1, %V
@ -2171,8 +2170,7 @@ define i1 @icmp_shl_1_V_sle_0(i32 %V) {
define <2 x i1> @icmp_shl_1_V_sle_0_vec(<2 x i32> %V) {
; CHECK-LABEL: @icmp_shl_1_V_sle_0_vec(
; CHECK-NEXT: [[SHL:%.*]] = shl nuw <2 x i32> <i32 1, i32 1>, [[V:%.*]]
; CHECK-NEXT: [[CMP:%.*]] = icmp slt <2 x i32> [[SHL]], <i32 1, i32 1>
; CHECK-NEXT: [[CMP:%.*]] = icmp eq <2 x i32> [[V:%.*]], <i32 31, i32 31>
; CHECK-NEXT: ret <2 x i1> [[CMP]]
;
%shl = shl <2 x i32> <i32 1, i32 1>, %V