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[InstCombine] Fix known bits handling in SimplifyDemandedUseBits
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Fixes a regression from D75801. SimplifyDemandedUseBits() is also
supposed to compute the known bits (of the demanded subset) of the
instruction. For unknown instructions it does so by directly calling
computeKnownBits(). For known instructions it will compute known
bits itself. However, for instructions where only some cases are
handled directly (e.g. a constant shift amount) the known bits
invocation for the unhandled case is sometimes missing. This patch
adds the missing calls and thus removes the main discrepancy with
ExpensiveCombines mode.

Differential Revision: https://reviews.llvm.org/D75804
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@nikic
nikic committed Mar 7, 2020
1 parent a4e71f0 commit 51a466a
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Showing 3 changed files with 36 additions and 72 deletions.
25 changes: 19 additions & 6 deletions llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
View file
Expand Up @@ -521,6 +521,8 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
// low bits known zero.
if (ShiftAmt)
Known.Zero.setLowBits(ShiftAmt);
} else {
computeKnownBits(I, Known, Depth, CxtI);
}
break;
}
Expand All @@ -544,6 +546,8 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
Known.One.lshrInPlace(ShiftAmt);
if (ShiftAmt)
Known.Zero.setHighBits(ShiftAmt); // high bits known zero.
} else {
computeKnownBits(I, Known, Depth, CxtI);
}
break;
}
Expand Down Expand Up @@ -604,6 +608,8 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
} else if (Known.One[BitWidth-ShiftAmt-1]) { // New bits are known one.
Known.One |= HighBits;
}
} else {
computeKnownBits(I, Known, Depth, CxtI);
}
break;
}
Expand All @@ -625,6 +631,8 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
// Propagate zero bits from the input.
Known.Zero.setHighBits(std::min(
BitWidth, LHSKnown.Zero.countLeadingOnes() + RHSTrailingZeros));
} else {
computeKnownBits(I, Known, Depth, CxtI);
}
break;
}
Expand Down Expand Up @@ -683,7 +691,8 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
Known.Zero = APInt::getHighBitsSet(BitWidth, Leaders) & DemandedMask;
break;
}
case Instruction::Call:
case Instruction::Call: {
bool KnownBitsComputed = false;
if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
switch (II->getIntrinsicID()) {
default: break;
Expand Down Expand Up @@ -715,8 +724,6 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
NewVal->takeName(I);
return InsertNewInstWith(NewVal, *I);
}

// TODO: Could compute known zero/one bits based on the input.
break;
}
case Intrinsic::fshr:
Expand All @@ -741,6 +748,7 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
RHSKnown.Zero.lshr(BitWidth - ShiftAmt);
Known.One = LHSKnown.One.shl(ShiftAmt) |
RHSKnown.One.lshr(BitWidth - ShiftAmt);
KnownBitsComputed = true;
break;
}
case Intrinsic::x86_mmx_pmovmskb:
Expand Down Expand Up @@ -769,16 +777,21 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,

// We know that the upper bits are set to zero.
Known.Zero.setBitsFrom(ArgWidth);
return nullptr;
KnownBitsComputed = true;
break;
}
case Intrinsic::x86_sse42_crc32_64_64:
Known.Zero.setBitsFrom(32);
return nullptr;
KnownBitsComputed = true;
break;
}
}
computeKnownBits(V, Known, Depth, CxtI);

if (!KnownBitsComputed)
computeKnownBits(V, Known, Depth, CxtI);
break;
}
}

// If the client is only demanding bits that we know, return the known
// constant.
Expand Down
32 changes: 5 additions & 27 deletions llvm/test/Transforms/InstCombine/all-bits-shift.ll
View file
Expand Up @@ -13,33 +13,11 @@ target triple = "powerpc64-unknown-linux-gnu"
; ((2072 >> (L == 0)) >> 7) & 1
; is always zero.
define signext i32 @main() #1 {
; EXPENSIVE-OFF-LABEL: @main(
; EXPENSIVE-OFF-NEXT: entry:
; EXPENSIVE-OFF-NEXT: [[TMP0:%.*]] = load i32*, i32** @b, align 8
; EXPENSIVE-OFF-NEXT: [[TMP1:%.*]] = load i32, i32* @a, align 4
; EXPENSIVE-OFF-NEXT: [[LNOT:%.*]] = icmp eq i32 [[TMP1]], 0
; EXPENSIVE-OFF-NEXT: [[LNOT_EXT:%.*]] = zext i1 [[LNOT]] to i32
; EXPENSIVE-OFF-NEXT: [[SHR_I:%.*]] = lshr i32 2072, [[LNOT_EXT]]
; EXPENSIVE-OFF-NEXT: [[CALL_LOBIT:%.*]] = lshr i32 [[SHR_I]], 7
; EXPENSIVE-OFF-NEXT: [[TMP2:%.*]] = and i32 [[CALL_LOBIT]], 1
; EXPENSIVE-OFF-NEXT: [[TMP3:%.*]] = load i32, i32* [[TMP0]], align 4
; EXPENSIVE-OFF-NEXT: [[OR:%.*]] = or i32 [[TMP2]], [[TMP3]]
; EXPENSIVE-OFF-NEXT: store i32 [[OR]], i32* [[TMP0]], align 4
; EXPENSIVE-OFF-NEXT: [[TMP4:%.*]] = load i32, i32* @a, align 4
; EXPENSIVE-OFF-NEXT: [[LNOT_1:%.*]] = icmp eq i32 [[TMP4]], 0
; EXPENSIVE-OFF-NEXT: [[LNOT_EXT_1:%.*]] = zext i1 [[LNOT_1]] to i32
; EXPENSIVE-OFF-NEXT: [[SHR_I_1:%.*]] = lshr i32 2072, [[LNOT_EXT_1]]
; EXPENSIVE-OFF-NEXT: [[CALL_LOBIT_1:%.*]] = lshr i32 [[SHR_I_1]], 7
; EXPENSIVE-OFF-NEXT: [[TMP5:%.*]] = and i32 [[CALL_LOBIT_1]], 1
; EXPENSIVE-OFF-NEXT: [[OR_1:%.*]] = or i32 [[TMP5]], [[TMP3]]
; EXPENSIVE-OFF-NEXT: store i32 [[OR_1]], i32* [[TMP0]], align 4
; EXPENSIVE-OFF-NEXT: ret i32 [[OR_1]]
;
; EXPENSIVE-ON-LABEL: @main(
; EXPENSIVE-ON-NEXT: entry:
; EXPENSIVE-ON-NEXT: [[TMP0:%.*]] = load i32*, i32** @b, align 8
; EXPENSIVE-ON-NEXT: [[TMP1:%.*]] = load i32, i32* [[TMP0]], align 4
; EXPENSIVE-ON-NEXT: ret i32 [[TMP1]]
; CHECK-LABEL: @main(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[TMP0:%.*]] = load i32*, i32** @b, align 8
; CHECK-NEXT: [[TMP1:%.*]] = load i32, i32* [[TMP0]], align 4
; CHECK-NEXT: ret i32 [[TMP1]]
;
entry:
%0 = load i32*, i32** @b, align 8
Expand Down
51 changes: 12 additions & 39 deletions llvm/test/Transforms/InstCombine/known-bits.ll
View file
Expand Up @@ -3,16 +3,9 @@
; RUN: opt -S -instcombine -expensive-combines=1 < %s | FileCheck %s --check-prefixes=CHECK,EXPENSIVE-ON

define void @test_shl(i1 %x) {
; EXPENSIVE-OFF-LABEL: @test_shl(
; EXPENSIVE-OFF-NEXT: [[Y:%.*]] = zext i1 [[X:%.*]] to i8
; EXPENSIVE-OFF-NEXT: [[Z:%.*]] = shl i8 64, [[Y]]
; EXPENSIVE-OFF-NEXT: [[A:%.*]] = and i8 [[Z]], 1
; EXPENSIVE-OFF-NEXT: call void @sink(i8 [[A]])
; EXPENSIVE-OFF-NEXT: ret void
;
; EXPENSIVE-ON-LABEL: @test_shl(
; EXPENSIVE-ON-NEXT: call void @sink(i8 0)
; EXPENSIVE-ON-NEXT: ret void
; CHECK-LABEL: @test_shl(
; CHECK-NEXT: call void @sink(i8 0)
; CHECK-NEXT: ret void
;
%y = zext i1 %x to i8
%z = shl i8 64, %y
Expand All @@ -22,16 +15,9 @@ define void @test_shl(i1 %x) {
}

define void @test_lshr(i1 %x) {
; EXPENSIVE-OFF-LABEL: @test_lshr(
; EXPENSIVE-OFF-NEXT: [[Y:%.*]] = zext i1 [[X:%.*]] to i8
; EXPENSIVE-OFF-NEXT: [[Z:%.*]] = lshr i8 64, [[Y]]
; EXPENSIVE-OFF-NEXT: [[A:%.*]] = and i8 [[Z]], 1
; EXPENSIVE-OFF-NEXT: call void @sink(i8 [[A]])
; EXPENSIVE-OFF-NEXT: ret void
;
; EXPENSIVE-ON-LABEL: @test_lshr(
; EXPENSIVE-ON-NEXT: call void @sink(i8 0)
; EXPENSIVE-ON-NEXT: ret void
; CHECK-LABEL: @test_lshr(
; CHECK-NEXT: call void @sink(i8 0)
; CHECK-NEXT: ret void
;
%y = zext i1 %x to i8
%z = lshr i8 64, %y
Expand All @@ -41,16 +27,9 @@ define void @test_lshr(i1 %x) {
}

define void @test_ashr(i1 %x) {
; EXPENSIVE-OFF-LABEL: @test_ashr(
; EXPENSIVE-OFF-NEXT: [[Y:%.*]] = zext i1 [[X:%.*]] to i8
; EXPENSIVE-OFF-NEXT: [[Z:%.*]] = ashr i8 -16, [[Y]]
; EXPENSIVE-OFF-NEXT: [[A:%.*]] = and i8 [[Z]], 3
; EXPENSIVE-OFF-NEXT: call void @sink(i8 [[A]])
; EXPENSIVE-OFF-NEXT: ret void
;
; EXPENSIVE-ON-LABEL: @test_ashr(
; EXPENSIVE-ON-NEXT: call void @sink(i8 0)
; EXPENSIVE-ON-NEXT: ret void
; CHECK-LABEL: @test_ashr(
; CHECK-NEXT: call void @sink(i8 0)
; CHECK-NEXT: ret void
;
%y = zext i1 %x to i8
%z = ashr i8 -16, %y
Expand All @@ -60,15 +39,9 @@ define void @test_ashr(i1 %x) {
}

define void @test_udiv(i8 %x) {
; EXPENSIVE-OFF-LABEL: @test_udiv(
; EXPENSIVE-OFF-NEXT: [[Y:%.*]] = udiv i8 10, [[X:%.*]]
; EXPENSIVE-OFF-NEXT: [[Z:%.*]] = and i8 [[Y]], 64
; EXPENSIVE-OFF-NEXT: call void @sink(i8 [[Z]])
; EXPENSIVE-OFF-NEXT: ret void
;
; EXPENSIVE-ON-LABEL: @test_udiv(
; EXPENSIVE-ON-NEXT: call void @sink(i8 0)
; EXPENSIVE-ON-NEXT: ret void
; CHECK-LABEL: @test_udiv(
; CHECK-NEXT: call void @sink(i8 0)
; CHECK-NEXT: ret void
;
%y = udiv i8 10, %x
%z = and i8 %y, 64
Expand Down

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