[llvm] 8eaf00e - [TargetLowering][RISCV] Make expandCTLZ work for non-power of 2 types.
Craig Topper via llvm-commits
llvm-commits at lists.llvm.org
Tue Jul 12 11:36:59 PDT 2022
Author: Craig Topper
Date: 2022-07-12T11:36:37-07:00
New Revision: 8eaf00e04dba1b98acf8031b61d9488387a1066e
URL: https://github.com/llvm/llvm-project/commit/8eaf00e04dba1b98acf8031b61d9488387a1066e
DIFF: https://github.com/llvm/llvm-project/commit/8eaf00e04dba1b98acf8031b61d9488387a1066e.diff
LOG: [TargetLowering][RISCV] Make expandCTLZ work for non-power of 2 types.
To convert CTLZ to popcount we do
x = x | (x >> 1);
x = x | (x >> 2);
...
x = x | (x >>16);
x = x | (x >>32); // for 64-bit input
return popcount(~x);
This smears the most significant set bit across all of the bits
below it then inverts the remaining 0s and does a population count.
To support non-power of 2 types, the last shift amount must be
more than half of the size of the type. For i15, the last shift
was previously a shift by 4, with this patch we add another shift
of 8.
Fixes PR56457.
Differential Revision: https://reviews.llvm.org/D129431
Added:
Modified:
llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
llvm/test/CodeGen/RISCV/pr56457.ll
Removed:
################################################################################
diff --git a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index d08b195ea239e..5225d028c103c 100644
--- a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -7850,7 +7850,7 @@ SDValue TargetLowering::expandCTLZ(SDNode *Node, SelectionDAG &DAG) const {
// return popcount(~x);
//
// Ref: "Hacker's Delight" by Henry Warren
- for (unsigned i = 0; (1U << i) <= (NumBitsPerElt / 2); ++i) {
+ for (unsigned i = 0; (1U << i) < NumBitsPerElt; ++i) {
SDValue Tmp = DAG.getConstant(1ULL << i, dl, ShVT);
Op = DAG.getNode(ISD::OR, dl, VT, Op,
DAG.getNode(ISD::SRL, dl, VT, Op, Tmp));
diff --git a/llvm/test/CodeGen/RISCV/pr56457.ll b/llvm/test/CodeGen/RISCV/pr56457.ll
index 0877dd668f8a7..1858241d711f8 100644
--- a/llvm/test/CodeGen/RISCV/pr56457.ll
+++ b/llvm/test/CodeGen/RISCV/pr56457.ll
@@ -18,6 +18,9 @@ define i15 @foo(i15 %x) nounwind {
; CHECK-NEXT: slli a1, a0, 49
; CHECK-NEXT: srli a1, a1, 53
; CHECK-NEXT: or a0, a0, a1
+; CHECK-NEXT: slli a1, a0, 49
+; CHECK-NEXT: srli a1, a1, 57
+; CHECK-NEXT: or a0, a0, a1
; CHECK-NEXT: not a0, a0
; CHECK-NEXT: slli a0, a0, 49
; CHECK-NEXT: srli a0, a0, 49
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