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[ARM] Restore hasSideEffects flag on t2WhileLoopSetup #168948

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Merged
merged 1 commit into from
Nov 21, 2025
Merged

[ARM] Restore hasSideEffects flag on t2WhileLoopSetup #168948

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4 changes: 3 additions & 1 deletion llvm/lib/Target/ARM/ARMInstrThumb2.td
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Original file line number Diff line number Diff line change
Expand Up @@ -5584,7 +5584,8 @@ class t2LOL<dag oops, dag iops, string asm, string ops>
// Setup for the iteration count of a WLS. See t2WhileLoopSetup.
def arm_wlssetup
: SDNode<"ARMISD::WLSSETUP",
SDTypeProfile<1, 1, [SDTCisInt<0>, SDTCisSameAs<1, 0>]>>;
SDTypeProfile<1, 1, [SDTCisInt<0>, SDTCisSameAs<1, 0>]>,
[SDNPSideEffect]>;

// Low-overhead loops, While Loop Start branch. See t2WhileLoopStart
def arm_wls : SDNode<"ARMISD::WLS",
Expand Down Expand Up @@ -5668,6 +5669,7 @@ def t2DoLoopStartTP :
// t2WhileLoopSetup to setup LR and t2WhileLoopStart to perform the branch. Not
// valid after reg alloc, as it should be lowered during MVETPAndVPTOptimisations
// into a t2WhileLoopStartLR (or expanded).
let hasSideEffects = 1 in
def t2WhileLoopSetup :
t2PseudoInst<(outs GPRlr:$lr), (ins rGPR:$tc), 4, IIC_Br,
[(set i32:$lr, (arm_wlssetup i32:$tc))]>;
Expand Down
45 changes: 45 additions & 0 deletions llvm/test/CodeGen/Thumb2/LowOverheadLoops/pr168209.ll
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@@ -0,0 +1,45 @@
; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 6
; RUN: llc -mtriple=thumbv8.1m.main %s -o - | FileCheck %s

; Checks that t2WhileLoopSetup is not CSEd.

define i32 @test(i16 %arg) {
; CHECK-LABEL: test:
; CHECK: @ %bb.0: @ %bb
; CHECK-NEXT: push {r7, lr}
; CHECK-NEXT: uxth r0, r0
; CHECK-NEXT: wls lr, r0, .LBB0_4
; CHECK-NEXT: .LBB0_1: @ %bb3
; CHECK-NEXT: @ =>This Inner Loop Header: Depth=1
; CHECK-NEXT: le lr, .LBB0_1
; CHECK-NEXT: @ %bb.2: @ %bb2
; CHECK-NEXT: wls lr, r0, .LBB0_4
; CHECK-NEXT: .LBB0_3: @ %bb7
; CHECK-NEXT: @ =>This Inner Loop Header: Depth=1
; CHECK-NEXT: le lr, .LBB0_3
; CHECK-NEXT: .LBB0_4: @ %.critedge
; CHECK-NEXT: movs r0, #0
; CHECK-NEXT: pop {r7, pc}
bb:
%i = zext i16 %arg to i32
%i1 = icmp eq i16 %arg, 0
br i1 %i1, label %.critedge, label %bb3

bb2: ; preds = %bb3
br i1 %i1, label %.critedge, label %bb7

bb3: ; preds = %bb3, %bb
%i4 = phi i32 [ %i5, %bb3 ], [ 0, %bb ]
%i5 = add i32 %i4, 1
%i6 = icmp eq i32 %i5, %i
br i1 %i6, label %bb2, label %bb3

bb7: ; preds = %bb7, %bb2
%i8 = phi i32 [ %i9, %bb7 ], [ 0, %bb2 ]
%i9 = add i32 %i8, 1
%i10 = icmp eq i32 %i9, %i
br i1 %i10, label %.critedge, label %bb7

.critedge: ; preds = %bb7, %bb2, %bb
ret i32 0
}