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[SimplifyCFG] Support trunc nuw in chain of comparisons. #155087

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Merged
merged 2 commits into from
Aug 31, 2025
Merged

[SimplifyCFG] Support trunc nuw in chain of comparisons. #155087

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3a67ccf
[SimplifyCFG] Add test for trunc nuw in chain of comparisons. (NFC)
andjo403 Aug 24, 2025
c8ec9ed
[SimplifyCFG] Support trunc nuw in chain of comparisons.
andjo403 Aug 24, 2025
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9 changes: 9 additions & 0 deletions llvm/lib/Transforms/Utils/SimplifyCFG.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -612,6 +612,15 @@ struct ConstantComparesGatherer {
/// If CompValue is already set, the function is expected to fail if a match
/// is found but the value compared to is different.
bool matchInstruction(Instruction *I, bool isEQ) {
Value *Val;
if (match(I, m_NUWTrunc(m_Value(Val)))) {
// If we already have a value for the switch, it has to match!
if (!setValueOnce(Val))
return false;
UsedICmps++;
Vals.push_back(ConstantInt::get(cast<IntegerType>(Val->getType()), isEQ));
return true;
}
// If this is an icmp against a constant, handle this as one of the cases.
ICmpInst *ICI;
ConstantInt *C;
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73 changes: 73 additions & 0 deletions llvm/test/Transforms/SimplifyCFG/switch_create.ll
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Expand Up @@ -1192,3 +1192,76 @@ if.end:
ret void

}

define void @and_chain_trunc_nuw_i1_condition(i8 %x) {
; CHECK-LABEL: @and_chain_trunc_nuw_i1_condition(
; CHECK-NEXT: switch i8 [[X:%.*]], label [[IF_THEN:%.*]] [
; CHECK-NEXT: i8 4, label [[COMMON_RET:%.*]]
; CHECK-NEXT: i8 3, label [[COMMON_RET]]
; CHECK-NEXT: i8 2, label [[COMMON_RET]]
; CHECK-NEXT: i8 0, label [[COMMON_RET]]
; CHECK-NEXT: ]
; CHECK: common.ret:
; CHECK-NEXT: ret void
; CHECK: if.then:
; CHECK-NEXT: tail call void @foo1()
; CHECK-NEXT: br label [[COMMON_RET]]
;
%add = add nsw i8 %x, -2
%icmp = icmp ugt i8 %add, 2
%trunc = trunc nuw i8 %x to i1
%and = select i1 %icmp, i1 %trunc, i1 false
br i1 %and, label %if.then, label %if.end
if.then:
tail call void @foo1()
ret void
if.end:
ret void
}

define void @or_chain_trunc_nuw_i1_condition(i8 %x) {
; CHECK-LABEL: @or_chain_trunc_nuw_i1_condition(
; CHECK-NEXT: [[X_OFF:%.*]] = add i8 [[X:%.*]], -1
; CHECK-NEXT: [[SWITCH:%.*]] = icmp ult i8 [[X_OFF]], 2
; CHECK-NEXT: br i1 [[SWITCH]], label [[IF_THEN:%.*]], label [[COMMON_RET:%.*]]
; CHECK: common.ret:
; CHECK-NEXT: ret void
; CHECK: if.then:
; CHECK-NEXT: tail call void @foo1()
; CHECK-NEXT: br label [[COMMON_RET]]
;
%icmp = icmp eq i8 %x, 2
%trunc = trunc nuw i8 %x to i1
%or = select i1 %icmp, i1 true, i1 %trunc
br i1 %or, label %if.then, label %if.end
if.then:
tail call void @foo1()
ret void
if.end:
ret void
}

define void @neg_and_chain_trunc_i1_condition(i8 %x) {
; CHECK-LABEL: @neg_and_chain_trunc_i1_condition(
; CHECK-NEXT: [[ADD:%.*]] = add nsw i8 [[X:%.*]], -2
; CHECK-NEXT: [[ICMP:%.*]] = icmp ugt i8 [[ADD]], 2
; CHECK-NEXT: [[TRUNC:%.*]] = trunc i8 [[X]] to i1
; CHECK-NEXT: [[AND:%.*]] = select i1 [[ICMP]], i1 [[TRUNC]], i1 false
; CHECK-NEXT: br i1 [[AND]], label [[IF_THEN:%.*]], label [[COMMON_RET:%.*]]
; CHECK: common.ret:
; CHECK-NEXT: ret void
; CHECK: if.then:
; CHECK-NEXT: tail call void @foo1()
; CHECK-NEXT: br label [[COMMON_RET]]
;
%add = add nsw i8 %x, -2
%icmp = icmp ugt i8 %add, 2
%trunc = trunc i8 %x to i1
%and = select i1 %icmp, i1 %trunc, i1 false
br i1 %and, label %if.then, label %if.end
if.then:
tail call void @foo1()
ret void
if.end:
ret void
}