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[InstCombine] Extend canonicalizeClampLike to handle truncated inputs
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This extends the canonicalizeClampLike function to allow cases where the
input is truncated, but still matching on the types of the ICmps. For
example
  %t = trunc i32 %X to i8
  %a = add i32 %X, 128
  %cmp = icmp ult i32 %a, 256
  %c = icmp sgt i32 %X, -1
  %f = select i1 %c, i8 High, i8 Low
  %r = select i1 %cmp, i8 %t, i8 %f
becomes
  %c1 = icmp slt i32 %X, -128
  %c2 = icmp sge i32 %X, 128
  %s1 = select i1 %c1, i32 sext(Low), i32 %X
  %s2 = select i1 %c2, i32 sext(High), i32 %s1
  %t = trunc i32 %s2 to i8
https://alive2.llvm.org/ce/z/vPzfxH

We limit the transform to constant High and Low values, where we know
the sext are free.

Differential Revision: https://reviews.llvm.org/D108049
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@davemgreen
davemgreen committed Oct 28, 2021
1 parent abb2a91 commit 9358384
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33 changes: 26 additions & 7 deletions llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1289,8 +1289,8 @@ Instruction *InstCombinerImpl::foldSelectValueEquivalence(SelectInst &Sel,
// Iff -C1 s<= C2 s<= C0-C1
// Also ULT predicate can also be UGT iff C0 != -1 (+invert result)
// SLT predicate can also be SGT iff C2 != INT_MAX (+invert res.)
static Instruction *canonicalizeClampLike(SelectInst &Sel0, ICmpInst &Cmp0,
InstCombiner::BuilderTy &Builder) {
static Value *canonicalizeClampLike(SelectInst &Sel0, ICmpInst &Cmp0,
InstCombiner::BuilderTy &Builder) {
Value *X = Sel0.getTrueValue();
Value *Sel1 = Sel0.getFalseValue();

Expand Down Expand Up @@ -1344,6 +1344,11 @@ static Instruction *canonicalizeClampLike(SelectInst &Sel0, ICmpInst &Cmp0,
if (!Sel1->hasOneUse())
return nullptr;

// If the types do not match, look through any truncs to the underlying
// instruction.
if (Cmp00->getType() != X->getType() && X->hasOneUse())
match(X, m_TruncOrSelf(m_Value(X)));

// We now can finish matching the condition of the outermost select:
// it should either be the X itself, or an addition of some constant to X.
Constant *C1;
Expand Down Expand Up @@ -1414,15 +1419,29 @@ static Instruction *canonicalizeClampLike(SelectInst &Sel0, ICmpInst &Cmp0,
if (!match(Precond2, m_One()))
return nullptr;

// If we are matching from a truncated input, we need to sext the
// ReplacementLow and ReplacementHigh values. Only do the transform if they
// are free to extend due to being constants.
if (X->getType() != Sel0.getType()) {
Constant *LowC, *HighC;
if (!match(ReplacementLow, m_ImmConstant(LowC)) ||
!match(ReplacementHigh, m_ImmConstant(HighC)))
return nullptr;
ReplacementLow = ConstantExpr::getSExt(LowC, X->getType());
ReplacementHigh = ConstantExpr::getSExt(HighC, X->getType());
}

// All good, finally emit the new pattern.
Value *ShouldReplaceLow = Builder.CreateICmpSLT(X, ThresholdLowIncl);
Value *ShouldReplaceHigh = Builder.CreateICmpSGE(X, ThresholdHighExcl);
Value *MaybeReplacedLow =
Builder.CreateSelect(ShouldReplaceLow, ReplacementLow, X);
Instruction *MaybeReplacedHigh =
SelectInst::Create(ShouldReplaceHigh, ReplacementHigh, MaybeReplacedLow);

return MaybeReplacedHigh;
// Create the final select. If we looked through a truncate above, we will
// need to retruncate the result.
Value *MaybeReplacedHigh = Builder.CreateSelect(
ShouldReplaceHigh, ReplacementHigh, MaybeReplacedLow);
return Builder.CreateTrunc(MaybeReplacedHigh, Sel0.getType());
}

// If we have
Expand Down Expand Up @@ -1513,8 +1532,8 @@ Instruction *InstCombinerImpl::foldSelectInstWithICmp(SelectInst &SI,
if (Instruction *NewAbs = canonicalizeAbsNabs(SI, *ICI, *this))
return NewAbs;

if (Instruction *NewAbs = canonicalizeClampLike(SI, *ICI, Builder))
return NewAbs;
if (Value *V = canonicalizeClampLike(SI, *ICI, Builder))
return replaceInstUsesWith(SI, V);

if (Instruction *NewSel =
tryToReuseConstantFromSelectInComparison(SI, *ICI, *this))
Expand Down
114 changes: 89 additions & 25 deletions llvm/test/Transforms/InstCombine/truncating-saturate.ll
View file
Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,7 @@
target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"

declare void @use(i32)
declare void @use16(i16)
declare void @use1(i1)

define i8 @testi16i8(i16 %add) {
Expand Down Expand Up @@ -57,13 +58,12 @@ define i32 @testi64i32(i64 %add) {

define i16 @testi32i16i8(i32 %add) {
; CHECK-LABEL: @testi32i16i8(
; CHECK-NEXT: [[A:%.*]] = add i32 [[ADD:%.*]], 128
; CHECK-NEXT: [[CMP:%.*]] = icmp ult i32 [[A]], 256
; CHECK-NEXT: [[T:%.*]] = trunc i32 [[ADD]] to i16
; CHECK-NEXT: [[C:%.*]] = icmp sgt i32 [[ADD]], -1
; CHECK-NEXT: [[F:%.*]] = select i1 [[C]], i16 127, i16 -128
; CHECK-NEXT: [[R:%.*]] = select i1 [[CMP]], i16 [[T]], i16 [[F]]
; CHECK-NEXT: ret i16 [[R]]
; CHECK-NEXT: [[TMP1:%.*]] = icmp sgt i32 [[ADD:%.*]], -128
; CHECK-NEXT: [[TMP2:%.*]] = select i1 [[TMP1]], i32 [[ADD]], i32 -128
; CHECK-NEXT: [[TMP3:%.*]] = icmp slt i32 [[TMP2]], 127
; CHECK-NEXT: [[TMP4:%.*]] = select i1 [[TMP3]], i32 [[TMP2]], i32 127
; CHECK-NEXT: [[TMP5:%.*]] = trunc i32 [[TMP4]] to i16
; CHECK-NEXT: ret i16 [[TMP5]]
;
%a = add i32 %add, 128
%cmp = icmp ult i32 %a, 256
Expand All @@ -76,13 +76,12 @@ define i16 @testi32i16i8(i32 %add) {

define <4 x i16> @testv4i32i16i8(<4 x i32> %add) {
; CHECK-LABEL: @testv4i32i16i8(
; CHECK-NEXT: [[A:%.*]] = add <4 x i32> [[ADD:%.*]], <i32 128, i32 128, i32 128, i32 128>
; CHECK-NEXT: [[CMP:%.*]] = icmp ult <4 x i32> [[A]], <i32 256, i32 256, i32 256, i32 256>
; CHECK-NEXT: [[T:%.*]] = trunc <4 x i32> [[ADD]] to <4 x i16>
; CHECK-NEXT: [[C:%.*]] = icmp sgt <4 x i32> [[ADD]], <i32 -1, i32 -1, i32 -1, i32 -1>
; CHECK-NEXT: [[F:%.*]] = select <4 x i1> [[C]], <4 x i16> <i16 127, i16 127, i16 127, i16 127>, <4 x i16> <i16 -128, i16 -128, i16 -128, i16 -128>
; CHECK-NEXT: [[R:%.*]] = select <4 x i1> [[CMP]], <4 x i16> [[T]], <4 x i16> [[F]]
; CHECK-NEXT: ret <4 x i16> [[R]]
; CHECK-NEXT: [[TMP1:%.*]] = icmp sgt <4 x i32> [[ADD:%.*]], <i32 -128, i32 -128, i32 -128, i32 -128>
; CHECK-NEXT: [[TMP2:%.*]] = select <4 x i1> [[TMP1]], <4 x i32> [[ADD]], <4 x i32> <i32 -128, i32 -128, i32 -128, i32 -128>
; CHECK-NEXT: [[TMP3:%.*]] = icmp slt <4 x i32> [[TMP2]], <i32 127, i32 127, i32 127, i32 127>
; CHECK-NEXT: [[TMP4:%.*]] = select <4 x i1> [[TMP3]], <4 x i32> [[TMP2]], <4 x i32> <i32 127, i32 127, i32 127, i32 127>
; CHECK-NEXT: [[TMP5:%.*]] = trunc <4 x i32> [[TMP4]] to <4 x i16>
; CHECK-NEXT: ret <4 x i16> [[TMP5]]
;
%a = add <4 x i32> %add, <i32 128, i32 128, i32 128, i32 128>
%cmp = icmp ult <4 x i32> %a, <i32 256, i32 256, i32 256, i32 256>
Expand All @@ -98,8 +97,8 @@ define i32 @testi32i32i8(i32 %add) {
; CHECK-NEXT: [[TMP1:%.*]] = icmp sgt i32 [[ADD:%.*]], -128
; CHECK-NEXT: [[TMP2:%.*]] = select i1 [[TMP1]], i32 [[ADD]], i32 -128
; CHECK-NEXT: [[TMP3:%.*]] = icmp slt i32 [[TMP2]], 127
; CHECK-NEXT: [[R:%.*]] = select i1 [[TMP3]], i32 [[TMP2]], i32 127
; CHECK-NEXT: ret i32 [[R]]
; CHECK-NEXT: [[TMP4:%.*]] = select i1 [[TMP3]], i32 [[TMP2]], i32 127
; CHECK-NEXT: ret i32 [[TMP4]]
;
%a = add i32 %add, 128
%cmp = icmp ult i32 %a, 256
Expand All @@ -115,8 +114,8 @@ define i16 @test_truncfirst(i32 %add) {
; CHECK-NEXT: [[TMP1:%.*]] = icmp sgt i16 [[T]], -128
; CHECK-NEXT: [[TMP2:%.*]] = select i1 [[TMP1]], i16 [[T]], i16 -128
; CHECK-NEXT: [[TMP3:%.*]] = icmp slt i16 [[TMP2]], 127
; CHECK-NEXT: [[R:%.*]] = select i1 [[TMP3]], i16 [[TMP2]], i16 127
; CHECK-NEXT: ret i16 [[R]]
; CHECK-NEXT: [[TMP4:%.*]] = select i1 [[TMP3]], i16 [[TMP2]], i16 127
; CHECK-NEXT: ret i16 [[TMP4]]
;
%t = trunc i32 %add to i16
%a = add i16 %t, 128
Expand Down Expand Up @@ -310,13 +309,12 @@ define i8 @testi32i8(i32 %add) {

define i16 @differentconsts(i32 %x, i16 %replacement_low, i16 %replacement_high) {
; CHECK-LABEL: @differentconsts(
; CHECK-NEXT: [[T0:%.*]] = icmp slt i32 [[X:%.*]], 128
; CHECK-NEXT: [[T1:%.*]] = select i1 [[T0]], i16 256, i16 -1
; CHECK-NEXT: [[T2:%.*]] = add i32 [[X]], 16
; CHECK-NEXT: [[T3:%.*]] = icmp ult i32 [[T2]], 144
; CHECK-NEXT: [[T4:%.*]] = trunc i32 [[X]] to i16
; CHECK-NEXT: [[R:%.*]] = select i1 [[T3]], i16 [[T4]], i16 [[T1]]
; CHECK-NEXT: ret i16 [[R]]
; CHECK-NEXT: [[TMP1:%.*]] = icmp slt i32 [[X:%.*]], -16
; CHECK-NEXT: [[TMP2:%.*]] = icmp sgt i32 [[X]], 127
; CHECK-NEXT: [[TMP3:%.*]] = trunc i32 [[X]] to i16
; CHECK-NEXT: [[TMP4:%.*]] = select i1 [[TMP1]], i16 256, i16 [[TMP3]]
; CHECK-NEXT: [[TMP5:%.*]] = select i1 [[TMP2]], i16 -1, i16 [[TMP4]]
; CHECK-NEXT: ret i16 [[TMP5]]
;
%t0 = icmp slt i32 %x, 128
%t1 = select i1 %t0, i16 256, i16 65535
Expand Down Expand Up @@ -570,6 +568,72 @@ define i32 @oneusethree(i64 %add) {
ret i32 %cond.i
}

define i16 @differentconsts_usetrunc(i32 %x, i16 %replacement_low, i16 %replacement_high) {
; CHECK-LABEL: @differentconsts_usetrunc(
; CHECK-NEXT: [[T0:%.*]] = icmp slt i32 [[X:%.*]], 128
; CHECK-NEXT: [[T1:%.*]] = select i1 [[T0]], i16 256, i16 -1
; CHECK-NEXT: [[T2:%.*]] = add i32 [[X]], 16
; CHECK-NEXT: [[T3:%.*]] = icmp ult i32 [[T2]], 144
; CHECK-NEXT: [[T4:%.*]] = trunc i32 [[X]] to i16
; CHECK-NEXT: [[R:%.*]] = select i1 [[T3]], i16 [[T4]], i16 [[T1]]
; CHECK-NEXT: call void @use16(i16 [[T4]])
; CHECK-NEXT: ret i16 [[R]]
;
%t0 = icmp slt i32 %x, 128
%t1 = select i1 %t0, i16 256, i16 65535
%t2 = add i32 %x, 16
%t3 = icmp ult i32 %t2, 144
%t4 = trunc i32 %x to i16
%r = select i1 %t3, i16 %t4, i16 %t1
call void @use16(i16 %t4)
ret i16 %r
}

define i16 @differentconsts_useadd(i32 %x, i16 %replacement_low, i16 %replacement_high) {
; CHECK-LABEL: @differentconsts_useadd(
; CHECK-NEXT: [[T2:%.*]] = add i32 [[X:%.*]], 16
; CHECK-NEXT: [[TMP1:%.*]] = icmp slt i32 [[X]], -16
; CHECK-NEXT: [[TMP2:%.*]] = icmp sgt i32 [[X]], 127
; CHECK-NEXT: [[TMP3:%.*]] = trunc i32 [[X]] to i16
; CHECK-NEXT: [[TMP4:%.*]] = select i1 [[TMP1]], i16 256, i16 [[TMP3]]
; CHECK-NEXT: [[TMP5:%.*]] = select i1 [[TMP2]], i16 -1, i16 [[TMP4]]
; CHECK-NEXT: call void @use(i32 [[T2]])
; CHECK-NEXT: ret i16 [[TMP5]]
;
%t0 = icmp slt i32 %x, 128
%t1 = select i1 %t0, i16 256, i16 65535
%t2 = add i32 %x, 16
%t3 = icmp ult i32 %t2, 144
%t4 = trunc i32 %x to i16
%r = select i1 %t3, i16 %t4, i16 %t1
call void @use(i32 %t2)
ret i16 %r
}

define i16 @differentconsts_useaddtrunc(i32 %x, i16 %replacement_low, i16 %replacement_high) {
; CHECK-LABEL: @differentconsts_useaddtrunc(
; CHECK-NEXT: [[T0:%.*]] = icmp slt i32 [[X:%.*]], 128
; CHECK-NEXT: [[T1:%.*]] = select i1 [[T0]], i16 256, i16 -1
; CHECK-NEXT: [[T2:%.*]] = add i32 [[X]], 16
; CHECK-NEXT: [[T3:%.*]] = icmp ult i32 [[T2]], 144
; CHECK-NEXT: [[T4:%.*]] = trunc i32 [[X]] to i16
; CHECK-NEXT: [[R:%.*]] = select i1 [[T3]], i16 [[T4]], i16 [[T1]]
; CHECK-NEXT: call void @use16(i16 [[T4]])
; CHECK-NEXT: call void @use(i32 [[T2]])
; CHECK-NEXT: ret i16 [[R]]
;
%t0 = icmp slt i32 %x, 128
%t1 = select i1 %t0, i16 256, i16 65535
%t2 = add i32 %x, 16
%t3 = icmp ult i32 %t2, 144
%t4 = trunc i32 %x to i16
%r = select i1 %t3, i16 %t4, i16 %t1
call void @use16(i16 %t4)
call void @use(i32 %t2)
ret i16 %r
}


define i8 @C0zero(i8 %X, i8 %y, i8 %z) {
; CHECK-LABEL: @C0zero(
; CHECK-NEXT: [[C:%.*]] = icmp slt i8 [[X:%.*]], -10
Expand Down

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