[llvm] [RISCV][WIP] Treat bf16->f32 as separate ExtKind in combineOp_VLToVWOp_VL. (PR #144653)
Craig Topper via llvm-commits
llvm-commits at lists.llvm.org
Wed Jun 18 01:54:20 PDT 2025
https://github.com/topperc created https://github.com/llvm/llvm-project/pull/144653
This allows us to better track the narrow type we need and to fix miscompiles if f16->f32 and bf16->f32 extends are mixed.
Fixes #144651.
Still need to add tests, but it's late and I need sleep.
>From c2f0ce3b14e466eeb22ce15d32ee85d1f573fb77 Mon Sep 17 00:00:00 2001
From: Craig Topper <craig.topper at sifive.com>
Date: Wed, 18 Jun 2025 01:50:43 -0700
Subject: [PATCH] [RISCV][WIP] Treat bf16->f32 as separate ExtKind in
combineOp_VLToVWOp_VL.
This allows us to better track the narrow type we need and to fix
miscompiles if f16->f32 and bf16->f32 extends are mixed.
Fixes #144651.
Still need to add tests, but it's late and I need sleep.
---
llvm/lib/Target/RISCV/RISCVISelLowering.cpp | 73 ++++++++++++---------
1 file changed, 42 insertions(+), 31 deletions(-)
diff --git a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
index e670567bd1844..f7d447e03af94 100644
--- a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -16309,7 +16309,12 @@ namespace {
// apply a combine.
struct CombineResult;
-enum ExtKind : uint8_t { ZExt = 1 << 0, SExt = 1 << 1, FPExt = 1 << 2 };
+enum ExtKind : uint8_t {
+ ZExt = 1 << 0,
+ SExt = 1 << 1,
+ FPExt = 1 << 2,
+ BF16Ext = 1 << 3
+};
/// Helper class for folding sign/zero extensions.
/// In particular, this class is used for the following combines:
/// add | add_vl | or disjoint -> vwadd(u) | vwadd(u)_w
@@ -16344,8 +16349,10 @@ struct NodeExtensionHelper {
/// instance, a splat constant (e.g., 3), would support being both sign and
/// zero extended.
bool SupportsSExt;
- /// Records if this operand is like being floating-Point extended.
+ /// Records if this operand is like being floating point extended.
bool SupportsFPExt;
+ /// Records if this operand is extended from bf16.
+ bool SupportsBF16Ext;
/// This boolean captures whether we care if this operand would still be
/// around after the folding happens.
bool EnforceOneUse;
@@ -16381,6 +16388,7 @@ struct NodeExtensionHelper {
case ExtKind::ZExt:
return RISCVISD::VZEXT_VL;
case ExtKind::FPExt:
+ case ExtKind::BF16Ext:
return RISCVISD::FP_EXTEND_VL;
}
llvm_unreachable("Unknown ExtKind enum");
@@ -16402,13 +16410,6 @@ struct NodeExtensionHelper {
if (Source.getValueType() == NarrowVT)
return Source;
- // vfmadd_vl -> vfwmadd_vl can take bf16 operands
- if (Source.getValueType().getVectorElementType() == MVT::bf16) {
- assert(Root->getSimpleValueType(0).getVectorElementType() == MVT::f32 &&
- Root->getOpcode() == RISCVISD::VFMADD_VL);
- return Source;
- }
-
unsigned ExtOpc = getExtOpc(*SupportsExt);
// If we need an extension, we should be changing the type.
@@ -16451,7 +16452,8 @@ struct NodeExtensionHelper {
// Determine the narrow size.
unsigned NarrowSize = VT.getScalarSizeInBits() / 2;
- MVT EltVT = SupportsExt == ExtKind::FPExt
+ MVT EltVT = SupportsExt == ExtKind::BF16Ext ? MVT::bf16
+ : SupportsExt == ExtKind::FPExt
? MVT::getFloatingPointVT(NarrowSize)
: MVT::getIntegerVT(NarrowSize);
@@ -16628,17 +16630,17 @@ struct NodeExtensionHelper {
EnforceOneUse = false;
}
- bool isSupportedFPExtend(SDNode *Root, MVT NarrowEltVT,
- const RISCVSubtarget &Subtarget) {
+ bool isSupportedFPExtend(MVT NarrowEltVT, const RISCVSubtarget &Subtarget) {
+ if (NarrowEltVT == MVT::f32)
+ return true;
// Any f16 extension will need zvfh
- if (NarrowEltVT == MVT::f16 && !Subtarget.hasVInstructionsF16())
- return false;
- // The only bf16 extension we can do is vfmadd_vl -> vfwmadd_vl with
- // zvfbfwma
- if (NarrowEltVT == MVT::bf16 && (!Subtarget.hasStdExtZvfbfwma() ||
- Root->getOpcode() != RISCVISD::VFMADD_VL))
- return false;
- return true;
+ if (NarrowEltVT == MVT::f16 && Subtarget.hasVInstructionsF16())
+ return true;
+ return false;
+ }
+
+ bool isSupportedBF16Extend(MVT NarrowEltVT, const RISCVSubtarget &Subtarget) {
+ return NarrowEltVT == MVT::bf16 && Subtarget.hasStdExtZvfbfwma();
}
/// Helper method to set the various fields of this struct based on the
@@ -16648,6 +16650,7 @@ struct NodeExtensionHelper {
SupportsZExt = false;
SupportsSExt = false;
SupportsFPExt = false;
+ SupportsBF16Ext = false;
EnforceOneUse = true;
unsigned Opc = OrigOperand.getOpcode();
// For the nodes we handle below, we end up using their inputs directly: see
@@ -16679,9 +16682,11 @@ struct NodeExtensionHelper {
case RISCVISD::FP_EXTEND_VL: {
MVT NarrowEltVT =
OrigOperand.getOperand(0).getSimpleValueType().getVectorElementType();
- if (!isSupportedFPExtend(Root, NarrowEltVT, Subtarget))
- break;
- SupportsFPExt = true;
+ if (isSupportedFPExtend(NarrowEltVT, Subtarget))
+ SupportsFPExt = true;
+ if (isSupportedBF16Extend(NarrowEltVT, Subtarget))
+ SupportsBF16Ext = true;
+
break;
}
case ISD::SPLAT_VECTOR:
@@ -16698,16 +16703,16 @@ struct NodeExtensionHelper {
if (Op.getOpcode() != ISD::FP_EXTEND)
break;
- if (!isSupportedFPExtend(Root, Op.getOperand(0).getSimpleValueType(),
- Subtarget))
- break;
-
unsigned NarrowSize = VT.getScalarSizeInBits() / 2;
unsigned ScalarBits = Op.getOperand(0).getValueSizeInBits();
if (NarrowSize != ScalarBits)
break;
- SupportsFPExt = true;
+ if (isSupportedFPExtend(Op.getOperand(0).getSimpleValueType(), Subtarget))
+ SupportsFPExt = true;
+ if (isSupportedBF16Extend(Op.getOperand(0).getSimpleValueType(),
+ Subtarget))
+ SupportsBF16Ext = true;
break;
}
default:
@@ -16940,6 +16945,11 @@ canFoldToVWWithSameExtensionImpl(SDNode *Root, const NodeExtensionHelper &LHS,
return CombineResult(NodeExtensionHelper::getFPExtOpcode(Root->getOpcode()),
Root, LHS, /*LHSExt=*/{ExtKind::FPExt}, RHS,
/*RHSExt=*/{ExtKind::FPExt});
+ if ((AllowExtMask & ExtKind::BF16Ext) && LHS.SupportsBF16Ext &&
+ RHS.SupportsBF16Ext && Root->getOpcode() == RISCVISD::VFMADD_VL)
+ return CombineResult(NodeExtensionHelper::getFPExtOpcode(Root->getOpcode()),
+ Root, LHS, /*LHSExt=*/{ExtKind::BF16Ext}, RHS,
+ /*RHSExt=*/{ExtKind::BF16Ext});
return std::nullopt;
}
@@ -16953,9 +16963,10 @@ static std::optional<CombineResult>
canFoldToVWWithSameExtension(SDNode *Root, const NodeExtensionHelper &LHS,
const NodeExtensionHelper &RHS, SelectionDAG &DAG,
const RISCVSubtarget &Subtarget) {
- return canFoldToVWWithSameExtensionImpl(
- Root, LHS, RHS, ExtKind::ZExt | ExtKind::SExt | ExtKind::FPExt, DAG,
- Subtarget);
+ return canFoldToVWWithSameExtensionImpl(Root, LHS, RHS,
+ ExtKind::ZExt | ExtKind::SExt |
+ ExtKind::FPExt | ExtKind::BF16Ext,
+ DAG, Subtarget);
}
/// Check if \p Root follows a pattern Root(LHS, ext(RHS))
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