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[InstCombine] Rotate transformation port from SelectionDAG to InstCombine #160628

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Merged
merged 6 commits into from
Sep 27, 2025
Merged

[InstCombine] Rotate transformation port from SelectionDAG to InstCombine #160628

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56dd41c
pre-commit
axelcool1234 Sep 25, 2025
021e1b6
The rotate transformation from https://github.com/llvm/llvm-project/b…
axelcool1234 Sep 25, 2025
1b3e617
added m_Deferred
axelcool1234 Sep 25, 2025
752eef0
Allow non-splat consant vectors
axelcool1234 Sep 25, 2025
2d53365
Switch to matching on APInt
axelcool1234 Sep 25, 2025
52f3d13
clang format
axelcool1234 Sep 25, 2025
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16 changes: 16 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 @@ -2405,6 +2405,22 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
matchBSwapOrBitReverse(*II, /*MatchBSwaps*/ true,
/*MatchBitReversals*/ true))
return BitOp;

// R = fshl(X, X, C2)
// fshl(R, R, C1) --> fshl(X, X, (C1 + C2) % bitsize)
Value *InnerOp;
const APInt *ShAmtInnerC, *ShAmtOuterC;
if (match(Op0, m_FShl(m_Value(InnerOp), m_Deferred(InnerOp),
m_APInt(ShAmtInnerC))) &&
match(ShAmtC, m_APInt(ShAmtOuterC)) && Op0 == Op1) {
APInt Sum = *ShAmtOuterC + *ShAmtInnerC;
APInt Modulo = Sum.urem(APInt(Sum.getBitWidth(), BitWidth));
if (Modulo.isZero())
return replaceInstUsesWith(*II, InnerOp);
Constant *ModuloC = ConstantInt::get(Ty, Modulo);
return CallInst::Create(cast<IntrinsicInst>(Op0)->getCalledFunction(),
{InnerOp, InnerOp, ModuloC});
}
}

// fshl(X, X, Neg(Y)) --> fshr(X, X, Y)
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72 changes: 72 additions & 0 deletions llvm/test/Transforms/InstCombine/fsh.ll
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Expand Up @@ -1214,3 +1214,75 @@ define i31 @fshr_neg_amount_non_power_two(i31 %x, i31 %y) {
%r = call i31 @llvm.fshr.i31(i31 %x, i31 %x, i31 %n)
ret i31 %r
}

define i32 @rot_const_consecutive(i32 %x) {
; CHECK-LABEL: @rot_const_consecutive(
; CHECK-NEXT: [[R2:%.*]] = call i32 @llvm.fshl.i32(i32 [[X:%.*]], i32 [[X]], i32 8)
; CHECK-NEXT: ret i32 [[R2]]
;
%r = call i32 @llvm.fshl.i32(i32 %x, i32 %x, i32 13)
%r2 = call i32 @llvm.fshl.i32(i32 %r, i32 %r, i32 27)
ret i32 %r2
}

define i32 @rot_const_consecutive_multi_use(i32 %x) {
; CHECK-LABEL: @rot_const_consecutive_multi_use(
; CHECK-NEXT: [[R:%.*]] = call i32 @llvm.fshl.i32(i32 [[X:%.*]], i32 [[X]], i32 7)
; CHECK-NEXT: [[R3:%.*]] = call i32 @llvm.fshl.i32(i32 [[X]], i32 [[X]], i32 11)
; CHECK-NEXT: [[R2:%.*]] = and i32 [[R]], [[R3]]
; CHECK-NEXT: ret i32 [[R2]]
;
%r = call i32 @llvm.fshl.i32(i32 %x, i32 %x, i32 7)
%r2 = call i32 @llvm.fshl.i32(i32 %r, i32 %r, i32 4)
%and = and i32 %r, %r2
ret i32 %and
}

define i32 @rot_const_consecutive_cancel_out(i32 %x) {
; CHECK-LABEL: @rot_const_consecutive_cancel_out(
; CHECK-NEXT: ret i32 [[X:%.*]]
;
%r = call i32 @llvm.fshl.i32(i32 %x, i32 %x, i32 7)
%r2 = call i32 @llvm.fshl.i32(i32 %r, i32 %r, i32 25)
ret i32 %r2
}

;; negative test, consecutive rotates only fold if shift amounts are const

define i32 @rot_nonconst_shift(i32 %x, i32 %amt) {
; CHECK-LABEL: @rot_nonconst_shift(
; CHECK-NEXT: [[R:%.*]] = call i32 @llvm.fshl.i32(i32 [[X:%.*]], i32 [[X]], i32 7)
; CHECK-NEXT: [[R2:%.*]] = call i32 @llvm.fshl.i32(i32 [[R]], i32 [[R]], i32 [[AMT:%.*]])
; CHECK-NEXT: ret i32 [[R2]]
;
%r = call i32 @llvm.fshl.i32(i32 %x, i32 %x, i32 7)
%r2 = call i32 @llvm.fshl.i32(i32 %r, i32 %r, i32 %amt)
ret i32 %r2
}

;; negative test, 1st funnel shift isn't a rotate.

define i32 @fsh_rot(i32 %x, i32 %y) {
; CHECK-LABEL: @fsh_rot(
; CHECK-NEXT: [[FSH:%.*]] = call i32 @llvm.fshl.i32(i32 [[X:%.*]], i32 [[Y:%.*]], i32 7)
; CHECK-NEXT: [[R:%.*]] = call i32 @llvm.fshl.i32(i32 [[FSH]], i32 [[FSH]], i32 4)
; CHECK-NEXT: ret i32 [[R]]
;
%fsh = call i32 @llvm.fshl.i32(i32 %x, i32 %y, i32 7)
%r = call i32 @llvm.fshl.i32(i32 %fsh, i32 %fsh, i32 4)
ret i32 %r
}

;; negative test, 2nd funnel shift isn't a rotate.

define i32 @rot_fsh(i32 %x, i32 %y) {
; CHECK-LABEL: @rot_fsh(
; CHECK-NEXT: [[Y:%.*]] = call i32 @llvm.fshl.i32(i32 [[X:%.*]], i32 [[X]], i32 7)
; CHECK-NEXT: [[R2:%.*]] = call i32 @llvm.fshl.i32(i32 [[Y]], i32 [[R:%.*]], i32 4)
; CHECK-NEXT: ret i32 [[R2]]
;
%r = call i32 @llvm.fshl.i32(i32 %x, i32 %x, i32 7)
%r2 = call i32 @llvm.fshl.i32(i32 %r, i32 %y, i32 4)
ret i32 %r2
}