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[InstSimplify] ctlz({signbit} >>u x) --> x 

The motivating pattern was handled in 0a2d69480d ,
but we should have this for symmetry.

But this really highlights that we could generalize for
any shifted constant if we match this in instcombine.

https://alive2.llvm.org/ce/z/MrmVNt
This commit is contained in:
Sanjay Patel 2021-03-15 11:44:53 -04:00
parent 3c93852a78
commit 660728acd4
2 changed files with 14 additions and 6 deletions
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6
llvm/lib/Analysis/InstructionSimplify.cpp
View File

@ -5470,6 +5470,12 @@ static Value *simplifyBinaryIntrinsic(Function *F, Value *Op0, Value *Op1,
return X;
break;
}
case Intrinsic::ctlz: {
Value *X;
if (match(Op0, m_LShr(m_SignMask(), m_Value(X))))
return X;
break;
}
case Intrinsic::smax:
case Intrinsic::smin:
case Intrinsic::umax:

14
llvm/test/Transforms/InstSimplify/call.ll
View File

@ -1381,6 +1381,8 @@ define <3 x i33> @cttz_shl1_vec(<3 x i33> %x) {
ret <3 x i33> %r
}
; Negative test - this could be generalized in instcombine though.
define i32 @cttz_shl_not_low_bit(i32 %x) {
; CHECK-LABEL: @cttz_shl_not_low_bit(
; CHECK-NEXT: [[S:%.*]] = shl i32 2, [[X:%.*]]
@ -1397,9 +1399,7 @@ declare <3 x i33> @llvm.ctlz.v3i33(<3 x i33>, i1)
define i32 @ctlz_lshr_sign_bit(i32 %x) {
; CHECK-LABEL: @ctlz_lshr_sign_bit(
; CHECK-NEXT: [[S:%.*]] = lshr i32 -2147483648, [[X:%.*]]
; CHECK-NEXT: [[R:%.*]] = call i32 @llvm.ctlz.i32(i32 [[S]], i1 true)
; CHECK-NEXT: ret i32 [[R]]
; CHECK-NEXT: ret i32 [[X:%.*]]
;
%s = lshr i32 2147483648, %x
%r = call i32 @llvm.ctlz.i32(i32 %s, i1 true)
@ -1408,15 +1408,15 @@ define i32 @ctlz_lshr_sign_bit(i32 %x) {
define <3 x i33> @ctlz_lshr_sign_bit_vec(<3 x i33> %x) {
; CHECK-LABEL: @ctlz_lshr_sign_bit_vec(
; CHECK-NEXT: [[S:%.*]] = lshr <3 x i33> <i33 undef, i33 -4294967296, i33 -4294967296>, [[X:%.*]]
; CHECK-NEXT: [[R:%.*]] = call <3 x i33> @llvm.ctlz.v3i33(<3 x i33> [[S]], i1 false)
; CHECK-NEXT: ret <3 x i33> [[R]]
; CHECK-NEXT: ret <3 x i33> [[X:%.*]]
;
%s = lshr <3 x i33> <i33 undef, i33 4294967296, i33 4294967296>, %x
%r = call <3 x i33> @llvm.ctlz.v3i33(<3 x i33> %s, i1 false)
ret <3 x i33> %r
}
; Negative test - this could be generalized in instcombine though.
define i32 @ctlz_lshr_not_sign_bit(i32 %x) {
; CHECK-LABEL: @ctlz_lshr_not_sign_bit(
; CHECK-NEXT: [[S:%.*]] = lshr i32 -1, [[X:%.*]]
@ -1428,6 +1428,8 @@ define i32 @ctlz_lshr_not_sign_bit(i32 %x) {
ret i32 %r
}
; TODO: Reduce to 0.
define i32 @ctlz_ashr_sign_bit(i32 %x) {
; CHECK-LABEL: @ctlz_ashr_sign_bit(
; CHECK-NEXT: [[S:%.*]] = ashr i32 -2147483648, [[X:%.*]]