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[InstSimplify] fold min/max with limit constant

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This is already done within InstCombine:
https://alive2.llvm.org/ce/z/MiGE22

...but leaving it out of analysis makes it
harder to avoid infinite loops there.

(cherry picked from commit e260e10c4a21784c146c94a2a14b7e78b09a9cf7)
This commit is contained in:
Sanjay Patel 2021-08-10 10:57:25 -04:00 committed by Tom Stellard
parent de802b8e6e
commit 5a14ea148e
4 changed files with 38 additions and 12 deletions
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4
include/llvm/Analysis/ValueTracking.h
View File

@ -744,6 +744,10 @@ constexpr unsigned MaxAnalysisRecursionDepth = 6;
/// minimum/maximum flavor.
CmpInst::Predicate getInverseMinMaxPred(SelectPatternFlavor SPF);
/// Return the minimum or maximum constant value for the specified integer
/// min/max flavor and type.
APInt getMinMaxLimit(SelectPatternFlavor SPF, unsigned BitWidth);
/// Check if the values in \p VL are select instructions that can be converted
/// to a min or max (vector) intrinsic. Returns the intrinsic ID, if such a
/// conversion is possible, together with a bool indicating whether all select

16
lib/Analysis/InstructionSimplify.cpp
View File

@ -4080,6 +4080,22 @@ static Value *simplifySelectWithICmpCond(Value *CondVal, Value *TrueVal,
std::swap(TrueVal, FalseVal);
}
// Check for integer min/max with a limit constant:
// X > MIN_INT ? X : MIN_INT --> X
// X < MAX_INT ? X : MAX_INT --> X
if (TrueVal->getType()->isIntOrIntVectorTy()) {
Value *X, *Y;
SelectPatternFlavor SPF =
matchDecomposedSelectPattern(cast<ICmpInst>(CondVal), TrueVal, FalseVal,
X, Y).Flavor;
if (SelectPatternResult::isMinOrMax(SPF) && Pred == getMinMaxPred(SPF)) {
APInt LimitC = getMinMaxLimit(getInverseMinMaxFlavor(SPF),
X->getType()->getScalarSizeInBits());
if (match(Y, m_SpecificInt(LimitC)))
return X;
}
}
if (Pred == ICmpInst::ICMP_EQ && match(CmpRHS, m_Zero())) {
Value *X;
const APInt *Y;

10
lib/Analysis/ValueTracking.cpp
View File

@ -6253,6 +6253,16 @@ CmpInst::Predicate llvm::getInverseMinMaxPred(SelectPatternFlavor SPF) {
return getMinMaxPred(getInverseMinMaxFlavor(SPF));
}
APInt llvm::getMinMaxLimit(SelectPatternFlavor SPF, unsigned BitWidth) {
switch (SPF) {
case SPF_SMAX: return APInt::getSignedMaxValue(BitWidth);
case SPF_SMIN: return APInt::getSignedMinValue(BitWidth);
case SPF_UMAX: return APInt::getMaxValue(BitWidth);
case SPF_UMIN: return APInt::getMinValue(BitWidth);
default: llvm_unreachable("Unexpected flavor");
}
}
std::pair<Intrinsic::ID, bool>
llvm::canConvertToMinOrMaxIntrinsic(ArrayRef<Value *> VL) {
// Check if VL contains select instructions that can be folded into a min/max

20
test/Transforms/InstSimplify/maxmin.ll
View File

@ -3,9 +3,7 @@
define i8 @smax_min_limit(i8 %x) {
; CHECK-LABEL: @smax_min_limit(
; CHECK-NEXT: [[CMP:%.*]] = icmp sgt i8 [[X:%.*]], -128
; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i8 [[X]], i8 -128
; CHECK-NEXT: ret i8 [[SEL]]
; CHECK-NEXT: ret i8 [[X:%.*]]
;
%cmp = icmp sgt i8 %x, -128
%sel = select i1 %cmp, i8 %x, i8 -128
@ -14,9 +12,7 @@ define i8 @smax_min_limit(i8 %x) {
define i8 @smin_max_limit(i8 %x) {
; CHECK-LABEL: @smin_max_limit(
; CHECK-NEXT: [[CMP:%.*]] = icmp slt i8 [[X:%.*]], 127
; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i8 [[X]], i8 127
; CHECK-NEXT: ret i8 [[SEL]]
; CHECK-NEXT: ret i8 [[X:%.*]]
;
%cmp = icmp slt i8 %x, 127
%sel = select i1 %cmp, i8 %x, i8 127
@ -25,9 +21,7 @@ define i8 @smin_max_limit(i8 %x) {
define <2 x i8> @umax_min_limit(<2 x i8> %x) {
; CHECK-LABEL: @umax_min_limit(
; CHECK-NEXT: [[CMP:%.*]] = icmp ugt <2 x i8> [[X:%.*]], zeroinitializer
; CHECK-NEXT: [[SEL:%.*]] = select <2 x i1> [[CMP]], <2 x i8> [[X]], <2 x i8> zeroinitializer
; CHECK-NEXT: ret <2 x i8> [[SEL]]
; CHECK-NEXT: ret <2 x i8> [[X:%.*]]
;
%cmp = icmp ugt <2 x i8> %x, zeroinitializer
%sel = select <2 x i1> %cmp, <2 x i8> %x, <2 x i8> zeroinitializer
@ -36,15 +30,15 @@ define <2 x i8> @umax_min_limit(<2 x i8> %x) {
define i8 @umin_max_limit(i8 %x) {
; CHECK-LABEL: @umin_max_limit(
; CHECK-NEXT: [[CMP:%.*]] = icmp ult i8 [[X:%.*]], -1
; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i8 [[X]], i8 -1
; CHECK-NEXT: ret i8 [[SEL]]
; CHECK-NEXT: ret i8 [[X:%.*]]
;
%cmp = icmp ult i8 %x, 255
%sel = select i1 %cmp, i8 %x, i8 255
ret i8 %sel
}
; negative test - wrong limit
define i8 @smax_not_min_limit(i8 %x) {
; CHECK-LABEL: @smax_not_min_limit(
; CHECK-NEXT: [[CMP:%.*]] = icmp sgt i8 [[X:%.*]], -127
@ -56,6 +50,8 @@ define i8 @smax_not_min_limit(i8 %x) {
ret i8 %sel
}
; negative test - wrong limit
define i8 @smin_not_min_limit(i8 %x) {
; CHECK-LABEL: @smin_not_min_limit(
; CHECK-NEXT: [[CMP:%.*]] = icmp slt i8 [[X:%.*]], 0