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[flang] Fixed ieee_logb to behave for denormals. #83518

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Mar 1, 2024
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[flang] Fixed ieee_logb to behave for denormals. #83518

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30 changes: 29 additions & 1 deletion flang/lib/Optimizer/Builder/IntrinsicCall.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -4195,39 +4195,45 @@ mlir::Value IntrinsicLibrary::genIeeeLogb(mlir::Type resultType,
builder.create<mlir::arith::BitcastOp>(loc, intType, realVal);
mlir::Type i1Ty = builder.getI1Type();

int exponentBias, significandSize;
int exponentBias, significandSize, nonSignificandSize;
switch (bitWidth) {
case 16:
if (realType.isF16()) {
// kind=2: 1 sign bit, 5 exponent bits, 10 significand bits
exponentBias = (1 << (5 - 1)) - 1; // 15
significandSize = 10;
nonSignificandSize = 6;
break;
}
assert(realType.isBF16() && "unknown 16-bit real type");
// kind=3: 1 sign bit, 8 exponent bits, 7 significand bits
exponentBias = (1 << (8 - 1)) - 1; // 127
significandSize = 7;
nonSignificandSize = 9;
break;
case 32:
// kind=4: 1 sign bit, 8 exponent bits, 23 significand bits
exponentBias = (1 << (8 - 1)) - 1; // 127
significandSize = 23;
nonSignificandSize = 9;
break;
case 64:
// kind=8: 1 sign bit, 11 exponent bits, 52 significand bits
exponentBias = (1 << (11 - 1)) - 1; // 1023
significandSize = 52;
nonSignificandSize = 12;
break;
case 80:
// kind=10: 1 sign bit, 15 exponent bits, 1+63 significand bits
exponentBias = (1 << (15 - 1)) - 1; // 16383
significandSize = 64;
nonSignificandSize = 16 + 1;
break;
case 128:
// kind=16: 1 sign bit, 15 exponent bits, 112 significand bits
exponentBias = (1 << (15 - 1)) - 1; // 16383
significandSize = 112;
nonSignificandSize = 16;
break;
default:
llvm_unreachable("unknown real type");
Expand Down Expand Up @@ -4259,6 +4265,11 @@ mlir::Value IntrinsicLibrary::genIeeeLogb(mlir::Type resultType,
/*withElseRegion=*/true);
// X is non-zero finite -- result is unbiased exponent of X
builder.setInsertionPointToStart(&innerIfOp.getThenRegion().front());
mlir::Value isNormal = genIsFPClass(i1Ty, args, normalTest);
auto normalIfOp = builder.create<fir::IfOp>(loc, resultType, isNormal,
/*withElseRegion=*/true);
// X is normal
builder.setInsertionPointToStart(&normalIfOp.getThenRegion().front());
mlir::Value biasedExponent = builder.create<mlir::arith::ShRUIOp>(
loc, shiftLeftOne,
builder.createIntegerConstant(loc, intType, significandSize + 1));
Expand All @@ -4268,6 +4279,23 @@ mlir::Value IntrinsicLibrary::genIeeeLogb(mlir::Type resultType,
result = builder.create<fir::ConvertOp>(loc, resultType, result);
builder.create<fir::ResultOp>(loc, result);

// X is denormal -- result is (-exponentBias - ctlz(significand))
builder.setInsertionPointToStart(&normalIfOp.getElseRegion().front());
mlir::Value significand = builder.create<mlir::arith::ShLIOp>(
loc, intVal,
builder.createIntegerConstant(loc, intType, nonSignificandSize));
mlir::Value ctlz =
builder.create<mlir::math::CountLeadingZerosOp>(loc, significand);
mlir::Type i32Ty = builder.getI32Type();
result = builder.create<mlir::arith::SubIOp>(
loc, builder.createIntegerConstant(loc, i32Ty, -exponentBias),
builder.create<fir::ConvertOp>(loc, i32Ty, ctlz));
result = builder.create<fir::ConvertOp>(loc, resultType, result);
builder.create<fir::ResultOp>(loc, result);

builder.setInsertionPointToEnd(&innerIfOp.getThenRegion().front());
builder.create<fir::ResultOp>(loc, normalIfOp.getResult(0));

// X is infinity or NaN -- result is +infinity or NaN
builder.setInsertionPointToStart(&innerIfOp.getElseRegion().front());
result = builder.create<mlir::arith::ShRUIOp>(loc, shiftLeftOne, one);
Expand Down