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[InstCombine] Fold (add X, (sext/zext (icmp eq X, C))) #93840

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[InstCombine] Fold (add X, (sext/zext (icmp eq X, C))) #93840

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e51e643
[InstCombine] Add tests for folding `(add X, (sext/zext (icmp eq X, C…
goldsteinn May 30, 2024
bc2ae38
[InstCombine] Fold `(add X, (sext/zext (icmp eq X, C)))`
goldsteinn May 30, 2024
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18 changes: 18 additions & 0 deletions llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1694,6 +1694,24 @@ Instruction *InstCombinerImpl::visitAdd(BinaryOperator &I) {
return BinaryOperator::CreateOr(LHS, Zext);
}

{
Value *Cond, *Ext;
Constant *C;
// (add X, (sext/zext (icmp eq X, C)))
// -> (select (icmp eq X, C), (add C, (sext/zext 1)), X)
auto CondMatcher = m_CombineAnd(
m_Value(Cond), m_ICmp(Pred, m_Deferred(A), m_ImmConstant(C)));
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I think it might be a bit more elegant if you match m_Value(Cond) first and then do a second match call on Cond. Especially with this in a separate variable (so that m_Deferred occurs before the corresponding m_Value) I found this confusing.

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That will be flakey if X itself is a sext/zext of another value though no?


if (match(&I,
m_c_Add(m_Value(A),
m_CombineAnd(m_Value(Ext), m_ZExtOrSExt(CondMatcher)))) &&
Pred == ICmpInst::ICMP_EQ && Ext->hasOneUse()) {
Value *Add = isa<ZExtInst>(Ext) ? InstCombiner::AddOne(C)
: InstCombiner::SubOne(C);
return replaceInstUsesWith(I, Builder.CreateSelect(Cond, Add, A));
}
}

if (Instruction *Ashr = foldAddToAshr(I))
return Ashr;

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17 changes: 5 additions & 12 deletions llvm/test/Transforms/InstCombine/apint-shift.ll
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Expand Up @@ -240,8 +240,8 @@ define i23 @test11(i23 %x) {

define i47 @test12(i47 %X) {
; CHECK-LABEL: @test12(
; CHECK-NEXT: [[SH2:%.*]] = and i47 [[X:%.*]], -256
; CHECK-NEXT: ret i47 [[SH2]]
; CHECK-NEXT: [[SH1:%.*]] = and i47 [[X:%.*]], -256
; CHECK-NEXT: ret i47 [[SH1]]
;
%sh1 = ashr i47 %X, 8
%sh2 = shl i47 %sh1, 8
Expand All @@ -250,8 +250,8 @@ define i47 @test12(i47 %X) {

define <2 x i47> @test12_splat_vec(<2 x i47> %X) {
; CHECK-LABEL: @test12_splat_vec(
; CHECK-NEXT: [[SH2:%.*]] = and <2 x i47> [[X:%.*]], <i47 -256, i47 -256>
; CHECK-NEXT: ret <2 x i47> [[SH2]]
; CHECK-NEXT: [[SH1:%.*]] = and <2 x i47> [[X:%.*]], <i47 -256, i47 -256>
; CHECK-NEXT: ret <2 x i47> [[SH1]]
;
%sh1 = ashr <2 x i47> %X, <i47 8, i47 8>
%sh2 = shl <2 x i47> %sh1, <i47 8, i47 8>
Expand Down Expand Up @@ -564,14 +564,7 @@ define i40 @test26(i40 %A) {
; https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=9880
define i177 @ossfuzz_9880(i177 %X) {
; CHECK-LABEL: @ossfuzz_9880(
; CHECK-NEXT: [[A:%.*]] = alloca i177, align 8
; CHECK-NEXT: [[L1:%.*]] = load i177, ptr [[A]], align 4
; CHECK-NEXT: [[TMP1:%.*]] = icmp eq i177 [[L1]], -1
; CHECK-NEXT: [[B5_NEG:%.*]] = sext i1 [[TMP1]] to i177
; CHECK-NEXT: [[B14:%.*]] = add i177 [[L1]], [[B5_NEG]]
; CHECK-NEXT: [[TMP2:%.*]] = icmp eq i177 [[B14]], -1
; CHECK-NEXT: [[B1:%.*]] = zext i1 [[TMP2]] to i177
; CHECK-NEXT: ret i177 [[B1]]
; CHECK-NEXT: ret i177 0
;
%A = alloca i177
%L1 = load i177, ptr %A
Expand Down
58 changes: 58 additions & 0 deletions llvm/test/Transforms/InstCombine/fold-ext-eq-c-with-op.ll
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@@ -0,0 +1,58 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt < %s -passes=instcombine -S | FileCheck %s

declare void @use.i8(i8)
define i8 @fold_add_zext_eq_0(i8 %x) {
; CHECK-LABEL: @fold_add_zext_eq_0(
; CHECK-NEXT: [[R:%.*]] = call i8 @llvm.umax.i8(i8 [[X:%.*]], i8 1)
; CHECK-NEXT: ret i8 [[R]]
;
%x_eq = icmp eq i8 %x, 0
%x_eq_ext = zext i1 %x_eq to i8
%r = add i8 %x, %x_eq_ext
ret i8 %r
}

define <2 x i8> @fold_add_sext_eq_4_6(<2 x i6> %xx) {
; CHECK-LABEL: @fold_add_sext_eq_4_6(
; CHECK-NEXT: [[X:%.*]] = zext <2 x i6> [[XX:%.*]] to <2 x i8>
; CHECK-NEXT: [[X_EQ:%.*]] = icmp eq <2 x i8> [[X]], <i8 4, i8 -127>
; CHECK-NEXT: [[R:%.*]] = select <2 x i1> [[X_EQ]], <2 x i8> <i8 3, i8 -128>, <2 x i8> [[X]]
; CHECK-NEXT: ret <2 x i8> [[R]]
;
%x = zext <2 x i6> %xx to <2 x i8>
%x_eq = icmp eq <2 x i8> %x, <i8 4, i8 129>
%x_eq_ext = sext <2 x i1> %x_eq to <2 x i8>
%r = add <2 x i8> %x_eq_ext, %x
ret <2 x i8> %r
}
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Commuted tests?


define i8 @fold_add_zext_eq_0_fail_multiuse_exp(i8 %x) {
; CHECK-LABEL: @fold_add_zext_eq_0_fail_multiuse_exp(
; CHECK-NEXT: [[X_EQ:%.*]] = icmp eq i8 [[X:%.*]], 0
; CHECK-NEXT: [[X_EQ_EXT:%.*]] = zext i1 [[X_EQ]] to i8
; CHECK-NEXT: [[R:%.*]] = add i8 [[X_EQ_EXT]], [[X]]
; CHECK-NEXT: call void @use.i8(i8 [[X_EQ_EXT]])
; CHECK-NEXT: ret i8 [[R]]
;
%x_eq = icmp eq i8 %x, 0
%x_eq_ext = zext i1 %x_eq to i8
%r = add i8 %x, %x_eq_ext
call void @use.i8(i8 %x_eq_ext)
ret i8 %r
}

define i8 @fold_add_sext_eq_4_fail_wrong_cond(i8 %x, i8 %y) {
; CHECK-LABEL: @fold_add_sext_eq_4_fail_wrong_cond(
; CHECK-NEXT: [[X_EQ:%.*]] = icmp eq i8 [[Y:%.*]], 4
; CHECK-NEXT: [[X_EQ_EXT:%.*]] = sext i1 [[X_EQ]] to i8
; CHECK-NEXT: [[R:%.*]] = add i8 [[X_EQ_EXT]], [[X:%.*]]
; CHECK-NEXT: call void @use.i8(i8 [[X_EQ_EXT]])
; CHECK-NEXT: ret i8 [[R]]
;
%x_eq = icmp eq i8 %y, 4
%x_eq_ext = sext i1 %x_eq to i8
%r = add i8 %x, %x_eq_ext
call void @use.i8(i8 %x_eq_ext)
ret i8 %r
}
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