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[MLIR][ARITH] Adds missing foldings for truncf #128096

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Merged
merged 6 commits into from
Feb 21, 2025
Merged

[MLIR][ARITH] Adds missing foldings for truncf #128096

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913cf19
[MLIR][ARITH] Fold extf followed bt truncf and truncf followed by truncf
zahimoud Feb 20, 2025
695c83f
Fixes
zahimoud Feb 21, 2025
f66b1d3
Remove truncf(truncf(a)) folding
zahimoud Feb 21, 2025
35a039b
Some fixes
zahimoud Feb 21, 2025
d822206
Format
zahimoud Feb 21, 2025
a35ced9
Update mlir/lib/Dialect/Arith/IR/ArithOps.cpp
zahimoud Feb 21, 2025
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21 changes: 21 additions & 0 deletions mlir/lib/Dialect/Arith/IR/ArithOps.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1518,6 +1518,27 @@ LogicalResult arith::TruncIOp::verify() {
/// can be represented without precision loss.
OpFoldResult arith::TruncFOp::fold(FoldAdaptor adaptor) {
auto resElemType = cast<FloatType>(getElementTypeOrSelf(getType()));
if (auto extOp = getOperand().getDefiningOp<arith::ExtFOp>()) {
Value src = extOp.getIn();
auto srcType = cast<FloatType>(getElementTypeOrSelf(src.getType()));
auto intermediateType =
cast<FloatType>(getElementTypeOrSelf(extOp.getType()));
// Check if the srcType is representable in the intermediateType.
if (llvm::APFloatBase::isRepresentableBy(
srcType.getFloatSemantics(),
intermediateType.getFloatSemantics())) {
// truncf(extf(a)) -> truncf(a)
if (srcType.getWidth() > resElemType.getWidth()) {
setOperand(src);
return getResult();
}

// truncf(extf(a)) -> a
if (srcType == resElemType)
return src;
}
}

const llvm::fltSemantics &targetSemantics = resElemType.getFloatSemantics();
return constFoldCastOp<FloatAttr, FloatAttr>(
adaptor.getOperands(), getType(),
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39 changes: 39 additions & 0 deletions mlir/test/Dialect/Arith/canonicalize.mlir
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Expand Up @@ -714,6 +714,45 @@ func.func @extFPVectorConstant() -> vector<2xf128> {
return %0 : vector<2xf128>
}

// CHECK-LABEL: @truncExtf
// CHECK-NOT: truncf
// CHECK: return %arg0
func.func @truncExtf(%arg0: f32) -> f32 {
%extf = arith.extf %arg0 : f32 to f64
%trunc = arith.truncf %extf : f64 to f32
return %trunc : f32
}

// CHECK-LABEL: @truncExtf1
// CHECK-NOT: truncf
// CHECK: return %arg0
func.func @truncExtf1(%arg0: bf16) -> bf16 {
%extf = arith.extf %arg0 : bf16 to f32
%trunc = arith.truncf %extf : f32 to bf16
return %trunc : bf16
}

// CHECK-LABEL: @truncExtf2
// CHECK: %[[ARG0:.+]]: bf16
// CHECK: %[[EXTF:.*]] = arith.extf %[[ARG0:.+]] : bf16 to f32
// CHECK: %[[TRUNCF:.*]] = arith.truncf %[[EXTF:.*]] : f32 to f16
// CHECK: return %[[TRUNCF:.*]]
func.func @truncExtf2(%arg0: bf16) -> f16 {
%extf = arith.extf %arg0 : bf16 to f32
%trunc = arith.truncf %extf : f32 to f16
return %trunc : f16
}

// CHECK-LABEL: @truncExtf3
// CHECK: %[[ARG0:.+]]: f32
// CHECK: %[[CST:.*]] = arith.truncf %[[ARG0:.+]] : f32 to f16
// CHECK: return %[[CST:.*]]
func.func @truncExtf3(%arg0: f32) -> f16 {
%extf = arith.extf %arg0 : f32 to f64
%truncf = arith.truncf %extf : f64 to f16
return %truncf : f16
}

// TODO: We should also add a test for not folding arith.extf on information loss.
// This may happen when extending f8E5M2FNUZ to f16.

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