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[DAG] SelectionDAG::isKnownToBeAPowerOfTwo - add ISD::TRUNCATE handling and tests (#184365)

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Closes #181654
This commit is contained in:
Pranshu Goyal 2026-03-28 22:20:19 +05:30 committed by GitHub
parent 3f42ec658f
commit 9d6b92e29f
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GPG Key ID: B5690EEEBB952194
3 changed files with 48 additions and 11 deletions
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5
llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
View File

@ -4823,6 +4823,11 @@ bool SelectionDAG::isKnownToBeAPowerOfTwo(SDValue Val,
Depth + 1);
}
case ISD::TRUNCATE: {
return (OrZero || isKnownNeverZero(Val, Depth)) &&
isKnownToBeAPowerOfTwo(Val.getOperand(0), OrZero, Depth + 1);
}
case ISD::ROTL:
case ISD::ROTR:
return isKnownToBeAPowerOfTwo(Val.getOperand(0), DemandedElts, OrZero,

34
llvm/test/CodeGen/AArch64/knownpow2-trunc-orzero.ll Normal file
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@ -0,0 +1,34 @@
; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 6
; RUN: llc < %s -mtriple=arm64-unknown-unknown-gnu | FileCheck %s --check-prefix=CHECK
define i8 @pow2_trunc_orzero_false_notzero(i32 %x, i8 %z){
; CHECK-LABEL: pow2_trunc_orzero_false_notzero:
; CHECK: // %bb.0:
; CHECK-NEXT: and w8, w1, #0xff
; CHECK-NEXT: and w9, w0, #0x7
; CHECK-NEXT: lsr w0, w8, w9
; CHECK-NEXT: ret
%amt = and i32 %x, 7
%y = shl i32 1, %amt
%tr = trunc i32 %y to i8
%div = udiv i8 %z, %tr
ret i8 %div
}
define i8 @pow2_trunc_orzero_false_maybezero(i32 %x, i8 %z){
; CHECK-LABEL: pow2_trunc_orzero_false_maybezero:
; CHECK: // %bb.0:
; CHECK-NEXT: neg w8, w0
; CHECK-NEXT: and w9, w1, #0xff
; CHECK-NEXT: and w8, w0, w8
; CHECK-NEXT: and w8, w8, #0xff
; CHECK-NEXT: udiv w0, w9, w8
; CHECK-NEXT: ret
%neg_x = sub i32 0, %x
%y = and i32 %x, %neg_x
%tr = trunc i32 %y to i8
%div = udiv i8 %z, %tr
ret i8 %div
}

20
llvm/test/CodeGen/X86/known-pow2.ll
View File

@ -1344,12 +1344,11 @@ define i32 @pow2_blsi_sub(i32 %x, i32 %a) {
define i8 @pow2_trunc(i32 %x, i32 %a){
; CHECK-LABEL: pow2_trunc:
; CHECK: # %bb.0:
; CHECK-NEXT: movl %esi, %ecx
; CHECK-NEXT: negl %ecx
; CHECK-NEXT: andl %esi, %ecx
; CHECK-NEXT: movzbl %dil, %eax
; CHECK-NEXT: divb %cl
; CHECK-NEXT: movzbl %ah, %eax
; CHECK-NEXT: movl %esi, %eax
; CHECK-NEXT: negl %eax
; CHECK-NEXT: andl %esi, %eax
; CHECK-NEXT: decb %al
; CHECK-NEXT: andb %dil, %al
; CHECK-NEXT: # kill: def $al killed $al killed $eax
; CHECK-NEXT: retq
%neg_a = sub i32 0, %a
@ -1382,11 +1381,10 @@ define i8 @pow2_trunc_vec(<4 x i32> %x, <4 x i32> %a) {
; CHECK-NEXT: pxor %xmm2, %xmm2
; CHECK-NEXT: psubd %xmm1, %xmm2
; CHECK-NEXT: pand %xmm1, %xmm2
; CHECK-NEXT: movd %xmm2, %ecx
; CHECK-NEXT: movd %xmm0, %eax
; CHECK-NEXT: movzbl %al, %eax
; CHECK-NEXT: divb %cl
; CHECK-NEXT: movzbl %ah, %eax
; CHECK-NEXT: pcmpeqd %xmm1, %xmm1
; CHECK-NEXT: paddb %xmm2, %xmm1
; CHECK-NEXT: pand %xmm0, %xmm1
; CHECK-NEXT: movd %xmm1, %eax
; CHECK-NEXT: # kill: def $al killed $al killed $eax
; CHECK-NEXT: retq
%a.splat = shufflevector <4 x i32> %a, <4 x i32> poison, <4 x i32> zeroinitializer