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[InstCombine] Set zero_is_poison for ctlz/cttz if they are only used as shift amounts #85035

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Merged
merged 2 commits into from
Mar 13, 2024
Merged

[InstCombine] Set zero_is_poison for ctlz/cttz if they are only used as shift amounts #85035

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2c834ff
[InstCombine] Add pre-commit tests. NFC.
dtcxzyw Mar 13, 2024
6b62484
[InstCombine] Set zero_is_poison for ctlz/cttz if they are only used …
dtcxzyw Mar 13, 2024
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5 changes: 5 additions & 0 deletions llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -504,6 +504,11 @@ static Instruction *foldCttzCtlz(IntrinsicInst &II, InstCombinerImpl &IC) {
return IC.replaceInstUsesWith(II, ConstantInt::getNullValue(II.getType()));
}

// If ctlz/cttz is only used as a shift amount, set is_zero_poison to true.
if (II.hasOneUse() && match(Op1, m_Zero()) &&
match(II.user_back(), m_Shift(m_Value(), m_Specific(&II))))
return IC.replaceOperand(II, 1, IC.Builder.getTrue());

Constant *C;

if (IsTZ) {
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93 changes: 93 additions & 0 deletions llvm/test/Transforms/InstCombine/shift-cttz-ctlz.ll
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@@ -0,0 +1,93 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 4
; RUN: opt < %s -passes=instcombine -S | FileCheck %s

define i32 @shl_cttz_false(i32 %x, i32 %y) {
; CHECK-LABEL: define i32 @shl_cttz_false(
; CHECK-SAME: i32 [[X:%.*]], i32 [[Y:%.*]]) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[CTTZ:%.*]] = call i32 @llvm.cttz.i32(i32 [[Y]], i1 true), !range [[RNG0:![0-9]+]]
; CHECK-NEXT: [[RES:%.*]] = shl i32 [[X]], [[CTTZ]]
; CHECK-NEXT: ret i32 [[RES]]
;
entry:
%cttz = call i32 @llvm.cttz.i32(i32 %y, i1 false)
%res = shl i32 %x, %cttz
ret i32 %res
}

define i32 @shl_ctlz_false(i32 %x, i32 %y) {
; CHECK-LABEL: define i32 @shl_ctlz_false(
; CHECK-SAME: i32 [[X:%.*]], i32 [[Y:%.*]]) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[CTTZ:%.*]] = call i32 @llvm.ctlz.i32(i32 [[Y]], i1 true), !range [[RNG0]]
; CHECK-NEXT: [[RES:%.*]] = shl i32 [[X]], [[CTTZ]]
; CHECK-NEXT: ret i32 [[RES]]
;
entry:
%cttz = call i32 @llvm.ctlz.i32(i32 %y, i1 false)
%res = shl i32 %x, %cttz
ret i32 %res
}

define i32 @lshr_cttz_false(i32 %x, i32 %y) {
; CHECK-LABEL: define i32 @lshr_cttz_false(
; CHECK-SAME: i32 [[X:%.*]], i32 [[Y:%.*]]) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[CTTZ:%.*]] = call i32 @llvm.cttz.i32(i32 [[Y]], i1 true), !range [[RNG0]]
; CHECK-NEXT: [[RES:%.*]] = lshr i32 [[X]], [[CTTZ]]
; CHECK-NEXT: ret i32 [[RES]]
;
entry:
%cttz = call i32 @llvm.cttz.i32(i32 %y, i1 false)
%res = lshr i32 %x, %cttz
ret i32 %res
}

define i32 @ashr_cttz_false(i32 %x, i32 %y) {
; CHECK-LABEL: define i32 @ashr_cttz_false(
; CHECK-SAME: i32 [[X:%.*]], i32 [[Y:%.*]]) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[CTTZ:%.*]] = call i32 @llvm.cttz.i32(i32 [[Y]], i1 true), !range [[RNG0]]
; CHECK-NEXT: [[RES:%.*]] = ashr i32 [[X]], [[CTTZ]]
; CHECK-NEXT: ret i32 [[RES]]
;
entry:
%cttz = call i32 @llvm.cttz.i32(i32 %y, i1 false)
%res = ashr i32 %x, %cttz
ret i32 %res
}

define i32 @shl_cttz_false_multiuse(i32 %x, i32 %y) {
; CHECK-LABEL: define i32 @shl_cttz_false_multiuse(
; CHECK-SAME: i32 [[X:%.*]], i32 [[Y:%.*]]) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[CTTZ:%.*]] = call i32 @llvm.cttz.i32(i32 [[Y]], i1 false), !range [[RNG0]]
; CHECK-NEXT: call void @use(i32 [[CTTZ]])
; CHECK-NEXT: [[RES:%.*]] = shl i32 [[X]], [[CTTZ]]
; CHECK-NEXT: ret i32 [[RES]]
;
entry:
%cttz = call i32 @llvm.cttz.i32(i32 %y, i1 false)
call void @use(i32 %cttz)
%res = shl i32 %x, %cttz
ret i32 %res
}

define i32 @shl_cttz_as_lhs(i32 %x, i32 %y) {
; CHECK-LABEL: define i32 @shl_cttz_as_lhs(
; CHECK-SAME: i32 [[X:%.*]], i32 [[Y:%.*]]) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[CTTZ:%.*]] = call i32 @llvm.cttz.i32(i32 [[Y]], i1 false), !range [[RNG0]]
; CHECK-NEXT: [[RES:%.*]] = shl i32 [[CTTZ]], [[X]]
; CHECK-NEXT: ret i32 [[RES]]
;
entry:
%cttz = call i32 @llvm.cttz.i32(i32 %y, i1 false)
%res = shl i32 %cttz, %x
ret i32 %res
}

declare void @use(i32)
;.
; CHECK: [[RNG0]] = !{i32 0, i32 33}
;.